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Four Sing/es spectra with excitation energies and prominent peaks. 15 that their peaks did not overlap peaks in the spectra that were being obtained. The position of the standards relative to the detector was maintained so that the intensities of the prominent peaks in the stan— dard were approximately the same as the prominent peaks in the spectra that was being obtained. These peaks due to the standard provided energy calibrations of the prominent and low energy excitation gammas which were then used in turn to provide energy calibrations for weak and/or higher excitation gammas on other runs. All of the spectra analyses for these runs were done by computer program SAMPO (RouJ69) as modified and adapted to use on the Sigma-7 computer (MorC70). This program performs a search and then fits a peak (or multiple peaks) to a Gaussian(s) with exponential tails to a deter- mined background. The background, except in a few very rare instances, was fitted as a straight line to the immediately adjacent higher and lower continum. The area, centroid, energy, and errors are determined. Energy calibrations, using SAMPO, were generally done to third order least squares fitting. 2.1.2 The On—Line y-Y Coincidence Experiments Coincidence experiments were performed for three reasons. First, an observed coincidence between two gammas identifies that these two gammas are in cascade. If the threshold value for either one of them is known (even roughly) it is possible to determine which gamma rays feeds from a level and is at a lower excitation energy and 16 gamma ray which feeds into that level and occurs at a higher excitation energy. This ordering is vital for the accurate construction of the decay scheme. Second, some gammas are observed to be in coincidence with those from known contaminants and/or competing reactions. By this means, the list of these gammas which belong to the de—excitation of 118"Sb can be more accurately defined. Third, there are some gammas which are seen in the singles spectra but are not observed in the coincidence spectra. This means they are either not part of an observed cascade, the feeding to these gammas (or from these gammas) are so weak as to be below the statistical limit for identification, or the gamma rays may come from isomeric states whose lifetimes are long compared to the timing window of the coincidence system. Such gammas are placed in the decay scheme only if the energy difference between two previously established levels is the same as that of the gamma (within the limits of the error bars), and such a placement is consistent with the two qualifying statements just made. A Ge(Li) detector was set up on each side of the target chamber as shown in Fig. 2.2. The lead wedge between the two detectors reduced the backscatter between the detectors. The hole in the lead acted as a Faraday cup and the thickness of the lead was sufficient to almost completely eliminate the lead x-rays. The picture shows the two detec— tors arranged in 180° geometry. Generally the detectors were arranged symmetrically, where possible, in approximately 150° geometry which also 17 )“7COINC GEOMETRY BEAM ://TARGET 7.4% A 2.5% Ge(Li) 12:1 Ge(Li) 1 Pb BEAM STOP and "COMPTON SUPPRESSOR" 18 helped to reduce the Compton scattering and significantly reduced the 511—511 keV annihilation radiation from the positron decays that were produced. Further reduction was achieved, as can be seen in the fig— ure, by having the target slightly up—stream from center—line of the two detectors. A typical two—parameter coincidence arrangement was used. Timing signals from the two detectors were obtained via two constant fraction timing discriminators which were sent to a time to pulse height converter to obtain the coincidence timing signal. The energy signals and coinci— dence signal were sent to two separate ADC's feeding the Sigma—7 computer. Under computer code EVENT (BayD71) the address from each ADC for a coin— cidence event was written into the two halves of a word and stored on magnetic tape by the Sigma—7 computer. Thus, every detected coincidence event, regardless of origin, is recorded on the tape. The timing require- ments for this type of experiment were very simple. The cyclotron is a pulsed beam accelerator, whose beam bursts are about 0.2 nsec long, and at the energies used for these eXperiments the repetition period between beam bursts was greater than 65 nsec (rf frequency < 15 MHz). The beam intensity was adjusted to provide a singles rate of about 15,000 counts/ sec in each detector so that the probability of more than one event oc— curring per beam burst was very small. Further, since the overwhelming bulk of the events were prompt, the probability of a coincidence event occurring during the longer beam—Off period was very small, except for events due to radioactive decay, and these were either of known origin or identified through other experiments. Thus, any coincidence timing less than the 65 nsec would have been quite satisfactory. Normally a l9 resolving time (FWHM) 2T 2520 to 30 nsec was used. The data were recovered from the tapes by using program EVENT RECOVERY (GieG69). In this program up to eight selected gates may be recovered simultaneously for each pass of the tapes. It is also possible, by carefully choosing regions of background from the adjacent continuum, to produce spectra with the coincidence background subtracted. In general, this was done. Figure 2.3 shows the integral spectrum for one of the two detectors and the spectra for three selected gates. Each integral spectrum con— tains 3,700,000 coincidence events. Three coincidence experiments of this type were run, using the same detectors in each case. One was at a beam energy of 5.37 MeV, corresponding to a maximum excitation of 850 keV and contained 935,000 coincidence events. The second was at a beam energy of 5.54 MeV, corresponding to a maximum excitation of 1000 keV, and contained the 3,700,000 coincidence events. The third was at a beam energy of 5.83 MeV, corresponding to an maximum excitation of 1300 keV, contained 7,600,000 coincidence events.b Where background subtraction is used in the recovery of the gated spectra to be used for analysis, violent statistical fluctuations of the low count backgrounds are often observed. These fluctuations tend to mask detail. For this reason spectra recovered from these experi— ments were constructed by using a three channel binomial average of the Spectra of all the significant gates for these three experiments are shown in Appendix II. 20 oeat- - g Stat— ; = D 84"- _ w — 3 ¥ .— c: UJ _' UJ DJ .7 a E ._ a: a a! "‘ 8h0t— c0 _ g (D j '1 1r 3 :1» D - x o __ E3 w i :1- E :i- 3 C) B “ (\J (D i m H m E 2 1 3' _. ”7. U7 _. g ; G: LLD _J G: _ 0C L9 UJ i.— I: H 9911’ 1128’ 5 ‘ h0€\ a. 963’ I _ €68 ' 232- 1.; sta- ——-—.-_ - = ‘3.- 881— 3 an— ‘1— h0t’ .— -5-_ U) 3- m cu .. o a) m .. o a) m .. o a: m .. o c5 CD CD c3 c3 CD CD c: c: CD CD c5 CD CD CD c: CD C) H H H H H H H H H H 1—1 H H H H 1—4 H H Fig. 2.3 7*7 coincidence spectra showing an integral spectrum and three selected gates. 21 data points. The result was to markedly clarify the spectra and reduce confusion without loosing significant information. 2.1.3 The Fast Timing Experiments Two experiments were performed to try to identify any gammas that 118 may be associated with short—lived isomeric decays of Sb. Two metal plates 1 meter long and spaced about 2.5 cm apart have been inserted in the beam line from the cyclotron. The plates aredriven at a subharmonic of the cyclotron rf by a high voltage oscillator. The voltage on these plates displaces the beam sufficiently so that only every second, or third, etc., beam burst is allowed to pass through a pair of slits downstream from the plates. In this manner the time inter— val between beam bursts on target can be lengthened. During this off time a subroutine of computer program TOOTSIE (BayD71) made it possible to divide this time interval into as many as eight time blocks. The data received during each of these time blocks are separately processed by an ADC and stored. The beam off time, for the cyclotron frequencies at which we operated, could be chosen from about 30 to 500 nanoseconds. Thus it was possible to observe the decay of states whose lifetimes ranged from a few nanoseconds to a few hundred nanoseconds. The upper limit of this observation is provided by the simple limit of specific target activity during the cycle of off—times. Fortimztwo experimentstjmuzwere run, the time intervals during the off—time for the first were about 33 nanoseconds long and the time inter- 22 vals for the off-time for the second were about 5 nanoseconds long. Figure 2.4 shows the spectra for the prompt (beam on) block and for three of the delayed time blocks for the second experiment. Several gammas can be seen that have observable lifetimes. The analysis of these data will be discussed in Chapter III. 2.1.4 The Decay of 118Te Previously published evidence (LedC67a) indicates that 118Te decays only to the ground state of 1188b. An experiment was devised to see if this was true. The half—life of the ground state of 118Te is six days. The ground state of the daughter, 1188b, is 3.5 min. Thus the decay of the daughter would achieve equilibrium with the decay of 118Te very quickly. The background from this 118Sb decay would then tend to mask the radiations from the 118Te decay. A method was devised using an ion exchange column and a rapid reflux system to greatly reduce the activity of the daughter decay in the sample and thereby enhance the probability of seeing gamma rays in 118Sb. The method involved setting up a column where the Sn and Sb were retained by the column, but the Te was extracted. The Te sample was rapidly passed in front of the detector where its activity was counted. The sample was then recycled back through the column, removing any of the daughter that was formed by decay. A drawing of the system is shown in Fig. 2.5. 23 . l T :> a) 2 (11 (as...) 969~ K 069’ (.U‘Uies 86 (r) (.0 +— m C C C O. 00 00 Z L0 00 ”7. EB 07 up to O m :— ri E3 0 O .0— r) 899- 53 *— (n <0 ‘0 n (0 C C i“ C k F“ (U C ”9 209 00 r\- 3'. Q: E (I) .—1 e m T 13m 9911- » Jr 4r 1188- i J 828. l [98“.] 0&8’ l r 8288- (IJ‘J é6t‘ 88t- [UsaJ 89b- 88!- g”- hm- [UJ mt— 195.u1 69- OS- fioux us - (D In 3' 0') If) :1’ 0') (U H C) :1" 0') (U .-a C) U) 3‘ m (U .—¢ C) C) CD <3 C) <3 c5 CDCDiCD C) CD <3 C) CD <:> c3 C)<3 c5 C)< WBNNVHO 83d SlNl'lOO .mH . 82:61.15... 31 CHAPTER III THE EXPERIMENTAL ANALYSIS 3.0 Introduction This chapter will be an examination of the data obtained from the various experiments. The first part will be an analysis of the (p,ny) experiments. The gammas which are believed to belong to the deexcitation Of Sb will be analyzed. Part two will be an analysis of the coincidence data. Those gammas which are in cascade are identified. This information provides a further refinement of those gammas which are believed to be assoc- 8 iated with the energy level diagram of 11 Sb. The third part of this chapter examines the timing experiments. In this section a group of gammas associated with an isomeric state are identified and the half-life of the state is Obtained. 118 The fourth part of this chapter examines the Te experiment. The results of this experiment provided information that was useful in being able to draw some tentative condlusions about the spin assign— ments of the lower states. The charged particle spectra are analyzed in the fifth part. From the stripping process some levels are identified and their energies are derived, the relationship among the different spectra 32 is observed. 3.1 The Analysis of the (p,ny) Experiments For proton beam energies at the threshold for the 118 Sb ground state the only gammas detected of course, were those due to competing reactions and due to trace amounts of contaminants. At the highest beam energies used, up to 150 gammas were observed with energies between 50 to 1500 keV. One of the spectra in Figure 2.1 was taken at 6.20 MeV, which was the highest energy used. The sources of all of these gammas cannot be identified with complete certainty, but from this spectrum a table of all those gammas, reasonably believed to be associated with the excitation of 1185b are listed in Table 3.1. The relative intensities given are those that apply for this part— icular beam energy (6.20MeV). Certainly at other beam energies, the population density of the excited states will be different and consequently the intensities of the gammas depopulating those states would also be different. The intensities as listed are relative to the intensity of the 115.4 keV gamma taken as 100. The intensities are corrected for the efficiency of the detector by program SAMPO (op.cit.) which can have the efficiency calibration of the different detectors read into the program (DoeR71). The energy of each of the listed gammas was obtained from one of the following resources: two spectra were run at different beam energies, at different times, and run with different sets Of simultaneous cali- bration sources (see Section 2.1.1). The conditions under which each 33 TABLE 3.1 . 118* The Gammas Believed to Belong to the Energy Level Scheme of Sb Gamma AE energy (keV)a (keV) Intensitye Confidencef 103.67 0.13 5.85 1 109.96 0.43 1 1.44 l 1 112.29 0.15 g 3.25 f 1 3 : 115.40 0.05 i 100 . 1 1 é ; 128.38 0.10 ; 8.71 1 l ? l 147.01b 0.35 g 0.11 4 l . i l 153.67 1 0.11 i 1.85 , 1 l l 5 l . 117 i 158.29 ; 0.10 f 3.07 f 2 doublet Wlth Sb ; * . i 170.63 ; 0.10 : 2.03 2 doublet with 27A1 ; i i ; 187.72 3 0.10 5 5.18 1 1 197.12 E 0.12 g 1.04 4 E 207.91 3 0.14 l 0.97 4 ‘ 216.19 E 0.10 g 4.14 1 ' £ 1 220.27b i 0.11 3 1.48 4 l 232.80 2 0.14 i 1.42 2 i P 237.24 3 0.09 5 19.66 3 1 s i 5 238.46 t 0.09 § 101.05 j 1 l i ; 260.70b l 0.14 ; 0.85 g 4 f * i 273.23C : 0.14 l g 1 ' l E (51.02) : unresolved doublet ! 273.92 . 0.21 l l 1 l l l l l Table 3.1 (Cont'd.) ’— 34 278.11b 293.83b 297.90 304.52 317.90b 324.23 352.58 354.96b 367.80 374.53 379.96b 384.90 388.85b 413.26 416.91 456.08 462.90 464.48 473.83b 488.70d 489.94 506.74 538.68b 540.68b 0.10 0.10 0.20 1.16 1.74 9.33 44.63 (7.35) 8.79 2.55 2.19 1.96 20.71 13.24 1.07 2.26 3.30 1.38 3.52 intensity effected by 370 keV contaminant possible doublet 35 Table 3.1 (Cont'd.2) 558.83 0.13 0.65 4 563.88 0.10 14.46 1 567.73b 0.20 3.75 3 571.22 0.10 6.97 3 575.17 0.10 l 4.88 2 577.86b 0.10 E 2.11 2 614.15b 0.09 2 5.86 i 2 622.0 0.5 1 (4.58) 2 2 unresolved doublet 629.48 0.11 l 1.24 i 4 Unless otherwise noted all the listed energies from this point on fall into the classification (b) l 633.71 0.09 l 2.52 l 4 i ; 640.53 0.12 E 1.05 l 4 i 2 a 674.03 1 0.20 § 1.92 3 2 1 1 690.27 ! 0.18 ; 18.70 t 2 these four peaks are 692.6 E 0.60 g 2.07 , 2 all on top of the 694.03 E 0.60 ‘ 2.83 ; 2 broad 72Ge(n,n') peak 697.0 0.36 g 13.44 . 2 and tail 715.49 0.14 i 3.93 g 3 719.70 0.15 ; 2.53 E 2 l 4 737.28 0.10 . 11.23 i 1 . l 746.89 0.12 2.68 f 3 771.83C 0.25 3 ; 2 c (8.08) l unresolved doublet 772.47 0.25 I ; 2 l Table 3.1 (Cont'd.3) 36 '1‘-" iawh" “an- n «-H‘ HUM - “~‘- <_.—C..A Hfi-A‘“ “-1—— v—u;1_-.W -qu .—._.‘_ Hm. “-4 .ru-wv— 788.30 0.12 2.98 793.11 0.08 3.09 803.18 0.08 4.62 806.8 0.08 4.41 829.12 0.15 2.60 832.48 0.10 2.64 835.58 ‘ 0.08 1.83 853.1 1 0.48 . 1.75 860.73 0.07 3.00 863.38 1 0.04 4.28 867.06 E 0.10 4.10 878.12 g 0.10 2.28 914.81 : 0.17 <1.5 922.49 1 0.31 1.59 928.22 I 0.17 3.59 940.03 E 0.12 2.57 943.70 0.14 3.90 955.03 0.24 E 9.04 962.01 . 0.12 g 2.02 982.46 ! 0.14 ! 5.61 994.01 0.15 E 7.49 1006.1 0.43 E 1.22 1019.14 0.17 1 7.25 1030 3.8 i 4.66 L——_— -AAW . .._._————vv—_o.— ‘mv—“h. #—._4..__. 37 Table 3.1 (Cont'd.4) 1033 7.4 5.19 4 1039.84 0.10 3.34 4 1044.3 1.0 4.94 3 1055.84 0.07 4.27 4 1064.05 0.15 1.34 4 1068.07 0.08 . 3.96 4 E 1088.71 i 0.08 l 1 10 4 ; 1095.98 1 0.20 l 2.20 3 , , . 1 1116.48 l 0.10 3 2.16 3 L l 1 1 1130.32 i 0.14 l 8.47 , 3 l 1 1141.29 ; 0.09 l 3.15 l 4 1 1154.08 l 0.17 g 1.37 l 3 2 1180.76 E 0.08 g 8.71 g 4 5 1205.97 1 0.06 i 4.26 l 4 i 1 1234.54 g 0.13 i 3.54 l 4 1 1239.39 J 0.12 E 4.09 l 4 L 1 l .1 aFor energies listed without superscript, the value is obtained from two calibration spectra. b These energies were obtained from the calibration of the 6.20 MeV spectrum. CThese energies were derived from the energy difference of the levels between which the gamma was a transition. 38 Table 3.1 (Cont'd.5) dThese energies were obtained from only one of the two spectra of (a). 8Relative to the 115.4 keV gamma, taken as 100. They are corrected for detector efficiency, and are the values from spectra taken at a beam energy of 6.20 MeV (1670 keV of excitation). fFor a discussion of Confidence see section 3.1. 39 of these spectra was taken was carefully optimized to provide the best resolution possible. The analysis of each spectrum was done, using SAMPO (op. cit.), with the single purpose of obtaining the energies of the gammas with maximum precision. Those gamma energies listed in the Table 3.1 without a superscript are the values which were considered the most precise as obtained from these spectra. Where, for some rea- son, the energy Of a gamma could be analyzed with precision in only one of these two calibration spectra, this fact is noted by a super- script (a). From these two calibration spectra eighteen gammas, well separated from one another, were chosen whose energies were considered the most precise. These values were then used in the analysis of the 6.20 MeV spectra to obtain the energy of those gammas which were not observed, or were not sufficiently resolved from the background at lower excitation energies. The energy of these gammas is noted by a superscript (b). Finally where a doublet or group of gammas could not be resolved by the analysis program, the energy of each one was obtained by finding the energy difference between the levels for which the gamma represents a transition. These are noted by the superscript (C) . The column labelled confidence identifies the extent to which the experimental evidence substantiates a gamma as belonging to the level scheme of 118Sb. Confidence 1 indicates gammas which are identified by the excitation curves and/or Show unambiguous coincidences with other gammas which already have been reliably established as belonging 40 to 11836. Confidence 2 indicates gammas which show up intensely in the coincidence spectra and fit with one or more other gammas within the error limits to define an energy level. Confidence 3 indicates gammas which are seen in the coincidence from other gammas feeding into or out of the same level. This confidence is also given to gammas which fit into the level scheme because the energies, within errors, fit between two levels, but the level diagram, as constructed, indicates that no trans- itions into or out of these levels have been observed. An example of this latter is the 1154.1 keV gamma from the 1153.6 keV level to ground. Confidence 4 indicates gammas which for a variety of experimentally f 1188b but have marginal reasons are believed to belong to the levels 0 not been found to fit into the level scheme and could be fitted in only by creating some level for them to decay from, or some other such un— substantiated construct. 3.1.1 The Excitation Function Experiments AS the energyof the proton beam is increased above the threshold for the excitation of any level, the occupation of that level should 118Sn(p,ny) reaction, the Q = —4.478i0.0057 119S increase rapidly. For the MeV(0kaK63). For the most importantcompetingreactions,118Sn(p,Y) 118S b. and 1188n(p,p'Y) n, the Q value for the first is +5.12 MeV and the second is the inelastic scattering reaction. This means that at the 118 118 . . Sn(p,ny) Sb threshold of 4.516 MeV the beam energy is high enough so that lower excited states in the two competing reactions should be 41 highly populated. Increases in beam energy to 6.20 MeV, which was the highest used in this series of experiments, should cause only relatively small changes in the population of the lower excited states for both of these competing reactions. The target used had a thickness of about 15 mg/cmz. This means that at a proton beam energy of 5.2 MeV there was an energy loss of 500 keV in the target and a straggling of 84 keV. At 6.2 MeV the energy loss was 425 keV with a straggling of 83 keV. This means that any resonances or fine detail in the excitation of either the (p,ny) reaction or the competing reactions should be wiped out and changes in the shape of the excitation function due to the opening of new exit channels, e.g., the excitation of higher states feeding a level, should be masked. Valuable use was made of this fact. Two prominent gamma rays, not in cascade with one another, are produced in the deexcitation of 1198b. One is a 270.3 keV gamma from the reaction 118Sn(p,y)119me. The other is a 644.1 keV gamma produced from the reaction 118Sn(p,y)11998b (BerG67). The intensities of these two gammas are a smooth, monotonic and slightly increasing function of the beam energies that were used in these experiments. The areas of the peaks of these two gammas made excellent, internal normalization standards. The ratio between the two provided a check on the consistency of the analysis that was done on the different spectra. The ratio of the area of the peak for any gamma ray to the area of the 270.3 keV peak is computed from each spectrum. (i.e. for each different excitation energy). The graph of these relative areas vs 42 the excitation energy, for each gamma, then gives the curve of an excitation function. The shape of this curve provides evidence to decide if a gamma belongs to the excitation Of 118Sb or to something else. This shape also gives a clue as to whether a particular peak is possibly singlet or doublet and in some cases if a doublet, a clue to the threshold of each member. Table 3.2 is a list of all of the gammas for which meaningful curves of excitation could be drawn. Also listed is the excitation energy at which it (or they in the case of doublets) was first uniquely identified and a limit for the apparent threshold energy. The following several sections will be a discussion of each curve in turn. 3.1.2 The Curves of Excitation of the 644/270, 115/270 keV Gammas, and the (237, 238)/270 keV Doublet Figure 3.1 shows the curves of excitation of the 644/270.3 keV gamma reference peaks, the 115.4/270.3, and the (237.2, 238.5)/270.3 keV gammas. The curves are of the ratios of the peak areas plotted against the excitation energy above the ground state threshold for 118Sb. The broken 644/270 curve Shows the amount of variation from run to run that occurred in the analysis of the peak areas. The scatter of these data represents the precision with which the area of the peaks were Obtained in the course of the experiments. The scatter of this 644/270 curve has a mean of 0.23 and an average deviation or disperson from 43 TABLE 3.2 The Gamma Rays for which Excitation Curves were drawn, with the Apparent Threshold Gamma Ray(s) Excitation Energy E Apparent upper limit where first ~ of the threshold identified energy (keV) (keV) 115.4 170 170 332:: 290 I 270 + ”:38 doublet 158.3 ? E ? :;§:§ 340 i :38 doublet 456.1 650 620 563.9 820 800 324.2 360 340 374.5 590 550 737.3 820 800 462.9 685 650 216.2 590 l 550 352.6 930 (670) 304.5 820 650 (doublet?) 367.8 730 ? 650 44 lllll' as Sb) 5. 111111] w‘ri TTIII PEAK AREA/PEAK AREA OF 270 keV (”9 6 '_ Io'2 /° 0 o /X)§( 3% a; 237, 238 keV ,{-644/27O X X 11111111 Illll 1111111 I Fig. 3./ 1 X 1 1 1 1 1 1 1 200 400 600 800 1000 15b0 I400 I600 1800 ENERGY ABOVE GROUND LEVEL WeV) Curves of excitation for the 644, //5, 237, and 238 keV gamma rays. 45 the mean of 0.020. The standard deviation is 0.024. These last two numbers give a measure of the random error which would be valid for the curve of area ratios of every peak of comparable intensity. The curve of the 115.4 keV gamma ratio has the typical shape of the curve of excitation for a single gamma under these experimental circumstances. Reference will be made to this shape in later figures. The threshold for this gamma appears to be in the vicinity of 170 keV of excitation. The curve of the 237, 238 keV gamma ratio is that of a doublet which was unresolvable by the 2.5% detector that was used to take these data. Analysis of subsequent spectra taken with the LEPS (Low Energy Photon Spectroscopy) detector (see Appendix A) have shown the energy of these two members to be 237.2 keV and 238.5 keV. Since the shape of this curve is essentially the same as that of a single gamma, this indicates that the two members of this doublet have thresholds which are close to one another in energy. The threshold for the lower energy member of this pair appears to be about 270 keV. From the experience gained in examining the curves for other doublets in this study a very rough estimate would be that the threshold for the other member of this pair is within a 100 keV of that for the first. 3.1.3 The Curves of Excitation of the 158/270, 273/270, 456/270, and 564/270 keV Gammas Figure 3.2 shows the curves of excitation for the 158.3/270.3, the ) 273 keV /° I |58 keV 6; PEAK AREA /PEAK AREA OF 270 keV (“9 *(Sb 0 18 / .LAI l l l I l l l l 400 600 800 l000 l200 I400 I600 l800 ENERGY ABOVE GROUND LEVEL (keV) 1 0 200 Fig. 3.2 Curves of exc1tat/on for the /58, 273, 456, and 564 keV gamma rays. 47 (273.2, 273.9)/270.3, the 456.1/270.3, and the 563.9/270.3 keV gammas. The curves are of the ratios of the peak areas plotted against the l excitation energy above the ground state threshold for 18Sb. The 158.3 keV gamma ray presents a dilemma. At excitation energies 118 well below the threshold energy for the ground state of Sb a gamma of about this energy is readily identified. This gamma ray could be 117 117*Sn attributed to the excitation of 117Sn from the reaction, Sn(p,p') 9 due to a very small amount of 117Sn in the target. The deexcitation of 117* Sn is very strongly through a 158.5 keV level to ground. (In the radioactive decay of 2.5 hr 117 Sb, 99.6% of all the gamma rays observed are 158.5 keV.) (BeeD69) . At higher excitation energies other, weak mem— bers of this decay are seen which tends to confirm the possibility of small amounts of 117Sn in the target. An examination of the curve of excitation, however, indicates that the shape is wrong and that the intensity seems to be rising much too rapidly for a gamma ray produced by the above, (p,p') reaction (see Section 3.1.1). These observations lend credence to the suspicions, also aroused by the coincidence exper— iments (see Section 3.2.2), that there is a weak gamma ray of 158.3 keV 1188b. The curve of excitation does associated with the energy levels of not, however, lend itself to the establishment of a value for the thres- hold. The curve for 273/270 keV gamma(s) shows the shape expected for a doublet which our best detector has not been able to resolve. The analysis program SAMPO (op.cit.), forcnuaparticularlygyxxispectrum, separated the 48 two components into one of energy 273.3 keV and another of energy 273.7 keV. Subsequent analysis of the energy level and the levels for which these two gammas are transitions, provides the energies of these two gammas as 273.2 and 273.9 keV, respectively. As will be discussed further in Chapter IV it is believed that one of these two 273 keV components and a 324.2 keV gammas both depopulate the same energy level, the ratio of the area of the 324.2 keV gamma peak to that of the area of the composite 273 keV peak as a function of the excitation energy is shown in figure 3.3. This ratio is seen to make a dramatic change at about 700 keV above the threshold for the ground state. This would indicate that the threshold for the second component of the doublet, or the depopulation of a different level, occurs at about this energy. The threshold for the lower energy component of 273 keV peak appears to be at about 320 keV excitation. The thresholds for the 456.1 and the 563.9 keV gammas, which have the shape of singlets appear to be about 620 keV and 800 keV, respectively. 3.1.4 The Curves of Excitation of the 324/270, 374/270, 737/270, and 463/270 keV Gammas Figure 3.4 Shows the curves of excitation of the 324.2/270.3, the 374.5/270.3, the 737.3/270.3, and the 462.9/270.3 keV gammas. The curves are of the ratios of the peak areas plotted against the excitation energy above the ground state threshold for 1185b. 49 l.5 00 14+ 8 o . > 9 ° 9 o ‘13—- 0 °\ ‘ m [s N o o o 4 L2" 00 d 3:1 o < 2‘; 1.1- . Lu 0. \ ?. 0° 3‘ |.Cl’ ' g . < -9’ ‘ m a: ‘1 o x .8- .. < m a. ,7- . 0 .6“- - (3 5, J, 1 J, 1 L '300 500 700 900 1100 1300 1500 I700 ENERGY ABOVE GROUND LEVEL (keV) Fig. 3.3 Intensity ratio of the 324/273 keV gammas vs excitation energy. 50 l0' 0 " .a’<> '3 Rw’w 2 . % . go 463 keV x l- 7. sf 2 o 374 «av? / “- p° x/ / 0 5) o / D o a o O/ X D H- 737 Rev 5 o/ g" x o/ x/ Q / / \ I ° * < '0 " O /o / / m X 5 ° / a fi x it / ° X .9 / I f ? lCi 441 1 1 1 1 1 l 1 1 0 200 400 600 800 I000 l200 I400 I600 I800 ENERGY ABOVE GROUND LEVEL (ROW Fig. 3.4 Curves of excitation for the 324, 374, 463, and 737 keV gamma rays. 51 The curves for the first three of these show the shape of single gammas with thresholds at about 340, 550, and 800 keV, respectively. The curve for the 463 keV gamma ray raises some suspicions. It has the shape that indicates the possibility of a doublet with the second member having a threshold energy in the range of 1000 to 1100 keV. The threshold energy for the first member is about 650 keV. If there is a second member, its peak area/peak area of the 270.3 keV reference peak in 1198b at the highest energy above ground at which measurements were made (1670 keV) would be about 0.35 to 0.40. If this is true it would be a very weak gamma ray with an intensity about one—third of that of the more prominent member. No corroborative evidence for a second member has been found. 3.1.5 The Curves of Excitation of the 216/270, 304/270, 368/270, and 352/270 keV Gammas Figure 3.5 shows the curves of excitation for the 216.2/270.3, the 304.5/270.3, the 367.8/270.3, and the 352.6/270.3 keV gammas. The curves are of the ratios of the peak areas plotted against the excita— tion energy above the ground state threshold for 118Sb. This figure shows the last of the gammas whose thresholds were low enough and whose excitations were intense enough that meaningful excitations could be drawn. The curve for the 216.2 keV gamma ray is that of a single gamma with a threshold energy of about 550 keV. The areas of the peaks of the 352.6 keV gamma ray were so low that this curve is just about the limit 52 gamma rays. IO A " : 3 ~ . i! _ l g} 4 z ’ ‘ a: )(w” CD [~- I L" 304 keV z—k /o 1 c“ I )( 0" . ‘5 ' W : " 0 g /0 8 .4 :5 P 2l6 k v 4x v 4 0 a: ’1‘. 8D/ / 368 keV x A ‘ 35 A/Mssz keV \ '0: 1 <1 * . LU ’ . a: t - < '- 370 keV a X " Cl ‘ <1 _ 00/ ii] 0 Cr q a. / O -2 I '0 4L 1 l L n g 1 l 1 O 200 400 600 80 IOOO IZOO I400 IGOO I800 ENERGY ABOVE GROUND LEVEL (keV) Fig. 3.5 Curves of excitation for the 2/6, 304, 368, and 352 keV 53 of interpretable excitation data. The curve has the shape of a single gamma with a very crude threshold of around 670 keV. Because the data are very scattered the error in this threshold is very large. These data provided only a very rough upper value for the threshold. From the coincidence analysis (Section 3.2.2) the threshold appears to be just over 400 keV. The 304.5 keV gamma peak may be a doublet. This shape, however, is predicted upon the precision of the last point, at 1670 keV of excitation. As can be seen from the reference 644.1/270.3 keV gamma intensities (Figure 3.1) and the position of this point relative to the extrapolated curve in the other excitation curves, this particular point has a low level of precision. That is, an error bar, if a meaningful one could be constructed, would be large enough so that the argument as to whether the 304.5 keV gamma curve should be that of a singlet or a doublet is a moot point. If the 304.5 keV peak is a doublet, no other evidence of a second member has been observed. The threshold for this 304.5 keV peak is about 650 keV. The 367.8 keV gamma ray has a known companion of an energy of 370 keV. The small number of counts in the total peak precluded a reliable separa— tion of this doublet for this excitation analysis, so the composite was plotted. The 370 keV companion appears alone at energies below a thres- hold for belonging to the decay of an excited state of 1183b and its curve of excitation appears to have the growth characteristic of a gamma belonging to one of the competing reactions. From the intersections of 54 this 370 keV growth and the 367.8 keV composite, the curve of excita— tion can be extrapolated backward to provide a threshold for the 367.8 keV gamma ray of about 650 keV. 3.2 The Coincidence Experiments In using gamma—ray spectroscopy to study the energy levels of a nucleus, gamma-gamma coincidence experiments are probably the most im- portant tool. Knowing which gammas are in coincidence with one another provides crucial clues as to which gamma rays populate the same level and/or which gamma rays depOpulate that same level. The following two sections will discuss the coincidence experiments and the analysis of the coincidence data. Chapter TV will discuss the develOpment of the energy level diagram for 1188b from this, and all the other experimen- tal data. Figure 4.1 in that chapter shows the level scheme that ev— olved from these experiments. 3.2.1 The Three On—Line Y-Y Coincidence Experiments Of the three on—line gamma-gamma coincidence experiments performed, two were intrinsically of limited significance. The first, taken at a proton beam energy of 5.37 MeV (an excitation above ground of 850 keV) was limited by the low number of significant coincidence events rela— tive to the number associated with secondary reactions plus cyclotron and electronic troubles that occurred during the experiment. It had been hOped to use these data to delineate the feeding of, and help establish 55 the lowest levels of this isotope. Spectra showing the inegral gates of the two detectors and two selected gated spectra are shown in Fig- ure 3.6 A second coincidence experiment, taken at a beam energy of 5.54 MeV (1000 keV excitation above the ground state), had one—fourth the number of coincidence events as the third experiment. This reduced the sensitivity with which one could make the decision as to whether two gammas were or were not in coincidence. Figure 3.7 shows the integral gates of the two detectors and two selected gated spectra for this experiment. For the above reasons, these two experiments were used primarily as weighing and corroborative factors in the extensive examinations of the coincidences seen in the third experiment. The third experiment, undertaken at a beam energy of 5.82 MeV (1300 keV excitation above the ground state) provided the primary evidence for deciding that two or more gammas were or were not in coincidence. Figure 3.8 shows the int— egral gates of the two detectors and two selected gated spectra for this third experiment. 3.2.2. The Analysis of the On—Line Y-Y Coincidence Experiments. A spectrum obtained for a given gate from all of these coincidence spectra was analysed in the following manner: First, the peaks in the gated coincidence spectrum were compared to the same and adjacent peaks in a singles spectrum run at the same energy. Those whose intensity was enhanced (roughly by a factor of five or more) in the gated spectrum 56 .xcoitmtiuxm to smx emmc sm: mm.m to xmcmcm Emma m not ummtmm nmtumimw oat new cotumtmn comm cox ssctumqw \mcmmtcu one cctgccm mutqum mucmbiucicu «IA ©.m .mcu mmmzaz smzzmx rmm _ _ _ _i=- _ _ _a ___ _ei _ 8917 9917 Z 8 L i MEG >3 m: A O 98 V Cc V 600 V L Cc XX 00 6 7 7o 1 V 1 MM 9 VV AA 8!] CL? 8 L88 1 >9. omm u xm Co zzmhomdm J6: mm.m *6 Amtmcm Emma 6 Est “momma nmtum\mm 62* new Lotumtmb comm not autistm \mtmm*:\ och mcigocm mutqum mccmhiuciou Ana N.m .mim coo... mmmzzz szz9. er 9 69 1 66 311 9 V E 810 ww w. 2 av . 3.8 >3 m: i 9 1 m . a i .LU H 9 Zl.L 1 8 9 a: . C5c8 O E V 9 C XX 0 V V V Z 2246 I.HH A 8 V [TL Cc 1 VV >3 23 u G 8 2:58am .2685. i so i g i r A . i >3 mg: n xm CC zzmhomdm 49. rmm V66 0L6 916 8L8 ZEB ZLL 6'V69 SL9 69V 99V 988 VLE 818 862 L62 m:.3 m: 119 0L2 911 >3 oomH n xm CC zamhommm limomHZH 0621 0901 119 >3 oomfi n xm Cc zzmhowdm 49. mm. - “.2 .82 B .85 >9. 8. IIIIIIIIO IV 1 /0 - /O I. +33: com A «H: >3. 0m1)+/ H in/fl/x x\«/+ l 88. .82 8m 2 8.: >9. 8 >9. ¢O_ _\ >9. wmm\\ 0 no. A v I MVEd :10 VBHV Decay curves from the 33 nsec timing experiment. Fig. 3.// 69 early or "prompt" time end for the 69, 50, and 197 keV gammas. These two were examined again in the 5.2 nsec experiment and will be discussed there. The 69 keV gamma with a half-life of approximately 220 nsec has 120 been attributed to Sb. The 197 keV gamma has been identified with 19F (T = 87 nsec). The long lifetime 158 keV gamma may belong to the 1/2 decay of 117 Sb. As was discussed in Section 3.1.3 a gamma ray from the 117 158.5 keV level of Sn was observed in many experiments. There is, however, a 158.3 keV gamma which is believed to be part of the deexcit— 118Sb ation of . It cannot be ruled out that this long-lived 158 keV gamma is part of 1188 b. At the time these experiments were done it was not possible to use beam pulsing techniques to measure lifetimes longer than a few hundred nanoseconds, so the lifetime of this decay could not be measured. The 50 keV gamma ray is the only unidentified gamma seen in this experiment. With a half—life greater than 300 nsec it is intriguing. The energy level diagram as constructed has a 50.8 keV level which does not appear to decay to ground. (See Chapter IV and Figure 4.1). This could be such an unobserved gamma. Unfortunatedly this energy happens totmaexactlytfluaenergycfifthe summed x-rays of tin and in all experiments these x—rays have masked all attempts to try and identify any gamma ray of this energy that could be attributable to 1188b. Other than this observation in the 33 nsec timing experiment, no other direct evidence for a gamma ray of this energy was found. 70 3.4.2 The Analysis of the 5.2 nsec Experiment Figure 3.12 shows the four gammas that were observed in the del- ayed spectra, where the time intervals were 5.2 nsec. The 115 keV gamma ray shows a prompt component and a component which seems to have the same half—life as the 238, 104, and 188 keV gammas. A straight line was fitted through each set of data points using least squares fitting and the half-life calculated. The average of these four is 13.16 nsec with a standard deviation of :1.2 nsec. It seems apparent that all three of the gammas are fed from the same isomeric level, and that the 115 keV gamma is fed from other prompt levels as well as from the iso- meric level. 18 3.5 The Analysis of the 1 Te Experiment As the tentative details of the structure of the energy level ll88b began to take shape it appeared there are several low diagram of lying (<85 keV) energy levels from which no observed gamma radiation to ground takes place. There is a possibility that some of these levels 118T could be weakly fed by the electromagnetic decay of e. The tech— nique, as discussed in Chapter II, was to reduce the background due to the decay of the 1188b daughter to as low a level as possible. This was done by passing the radioactive sample, dissolved in solution, thr— ough an ion exchange column. The Sb and Sn were retained by the column and the effluent, Containing the Te, was rapidly passed in front of the detector from which it was re—cycled back through the column. 71 hzu20m<020m mmhm< oz o m .4 n N _ _ i - - _ i . 63 8 N86 with n IE; 02%. 9.: 54”.. - w 1. T - n H .I O l. /o/ l O/ l - o/o . - ill/IIIIIIO 1 I / 1 n >9. mm. .\\ o H ”/0 /A I / - flaflm/o/ - - ”mm/OJ >9. vo. . - /« // - \ ”o / .. >9. mnm «ilflm/im 1 89. N. 9 m3. . NS 23.: /im. 63.. 9.0 4 NS. . 8mm. 9.9 o . 82. «6.0 4 new. . .8: NS \\ - H 82 8.0 4 om... . a... 9.9 >9. 6.. H ”I 82. .md « 8.: u .«o: S.» 1.. O. 0. v 0. IO 30 VEHV MVEd Fig. 3.i2 Decay curves from the 5.2 nsec timing experiment. 72 Figure 2.6 shows the spectra from this experiment. As can be seen , , , , 119 118 in the spectra, copious quantities of Te as well as Te were produced. The reason why this was true are not germaine here, but as a consequence the observed enhancement of the 118 Te decay was not as high as would have been desired. However, an upper limit of the obser— vability of gamma rays due to the deexcitation of any low lying levels of 118Sb can be made though nothing can be said about the internal con- version electrons from these states. They are impossible to observe in this experiment as their energies are much too low to be detected under these experimental conditions. It is known that 2.5% of all known decays of 118 Sb go through the 1229 keV level of 118Sn (HatJ70). Using the spectra shown in Figure 2.8, the background in the vicinity of 100 keV, where any gammas of 118* . . 4 Sb would be expected to appear, contains approx1mately 6X10 counts/ Chan. The number of counts in the 1229 peak is 1450 counts. Bringing in the efficiency of the detector at these two energies and the self- absorption of the sample, it is then possible to say that there are 5 118 118 less than 2.5X10_ Sb gammas per decay of the Te nucleus. 3.6 The Charged Particle Spectra A total of 30 nuclear emulsion plates were exposed in the Enge charged particle spectrometer to 3He or 4He particles from the cyclo— tron for periods ranging from a trial of 1/2 an hour to several hours. The targets, of 117Sn, 118Sn, or 119Sn were 100—150 ug/cm2 on 30 Ug/cm2 carbon backing. The beam energy was usually from 30-35 MeV. 0f the 73 30 plates, 11 were of tracks of particles resulting from a reaction producing 118Sb, e.g. 118Sn(3He,t)1188b. Of these 11 plates, 7 were of sufficient quality that valuable data could be read from them. That is there were a sufficient number of tracks, and sufficient reso— lution, that a stripping of the peaks could lead to a reasonably reliable determination of the peak centroids. Of these seven plates, for 4 of them the data from the integration of the beam current on the Faraday cup were sufficiently consistent among the runs that relative intensity data could be used for analysis for angular momentum transfer. 3.6.1 The Analysis of the Charged Particle Spectra: The Ladder Diagram of Energies Figure 2.7a shows the best particle spectrum as read from the plate This spectrum is from a 118Sn(3He,t)118Sb reaction at 15°. The num— bering for the channels is arbitrary, but the datum for each channel is the number of tracks in the nuclear emulsion in a % mm scan across the width of the spectrum. In order to facilitate the identification of the individual peaks, improve the statistical symmetry, and aid in the establishment of the peak centroid via the stripping process, all of the spectra were smoothed using a three channel binomial average. This process greatly reduces the value of (Chi)2 at the minimum and thereby reduces the uncertainty in the estimate of the area. Even though the variance of the distribu- tion is increased by one-half,the increased symmetry greatly reduces the standard error of the centroid (BevP69). This smoothed spectrum is 74 shown in Figure 2.7b. A single reference peak shape with a centroid was derived from a smoothed average of several well defined peaks in the spectrum and is then used for a channel by channel stripping of the spectrum using the technique that is well known to scintillation spectroscopy. Figure 2.7c shows the stripping that was done on this spectrum. The channel number of the centroid was read to the nearest 1/3 of a channel, converted into cm of position along the plate. The area for each peak was calculated from the integral under the reference shape as it was fitted to the peak. The position of the centroids of the peaks plus the beam energy, reaction, target parameters, and settings of the spectrograph were fed into the computer program MONSTER (RicH70). The output provided an energy fit with statistical error. The fitting of the centroid of a peak by the stripping operation for the different spectra was easily reproduceable to 15—20 keV. The error due to smooth— ing and the low number of counts would preclude, however, assigning an error to the final energies for a given spectrum of less than i 30 keV. Figure 3.13 is a diagram showing the energies of the peaks which were read from the spectra on the seven plates. This ladder diagram shows the data from three different reactions. A dashed line indicates Additional spectra from the spectrographic plate data is shown in Appendix E. .mmtmE m. Emcmmtmem cm>mm mm cmlmmmt ammo::.m...vccm>: mCm omm:«m.mtm.cm>: .mmm\\:.mtm.cmmv: mi 2,. cmmm $.me mi 48 mm..mcmcm mi km Emcmmm cmmmmm TM .94 75 o.o .vo mm NV 1 m¢ 1 mm 1 _o_1 t IIIII 9. Illll oo. o. m _ _ IIIII 6.1 8.1 6.1 5.1 2.1 8. 11111 «m. IIIII 08 6mm 1 EN 1 4mm 1 mmm 1 08 11111 .98 oh 8N mxm 1 Now 08 m5 1 8mm 11111 0mm 1 own IIIII 6% .mm 1 8.6. 1 oxm 1 mom .9. 1 3m 1 8m 1 8.. 0.1m vmv 5v ||||| mm.» 1 mm... 1 mmv 1 806 1 08 on... 1 own 1 0mm 6.46 1 Sn 1 $6 1 Em $6 0.8 11111 mom 1 wow 1 .8 1 >8 1 08 .48 1 mmm 1 m .m 98 v8 IIIII 8m v8 mxm 1 N K 1 N. x IIIII 8.. $8 1 ti SK m3 1 WWW 11111 one $8 max 1 can 1 08 v8 mmm 1 mmm 1 mmm 1 Nmm 1 mvw 1. l mNm m5 1 m8 1 Km 1 Em 1 Sb 11111 _ .m 1 mom 1 com 1 mom 1 8mm 1 «om IIIII oom 8mm 1 :8 1 QB 1 «8 8m 1 1 . Nam 1 08 lllll 08 08. oNN om_ oNN 00— at at oxL .oO_ excrucmm: 261% awe. 2.65.59. ...m...m.cmm_. .udImvcmE c6395.... 2.6.16.5... (A3!) ASHBNE 76 a peak with too few counts to define a shape and a reliable centroid, or a peak whose precise position was difficult to ascertain because of the overlap with closely adjacent peaks on either side. In either case the peak is there but the energy is not certain and the energy error would have to be stated as much larger than i 30 keV. The energy shown is obtained from the best value for the centroid of the peak that a judgement could make in the presence of poor statistics. The ladder diagram shows the consistency of some of these low energy, weak excited States . 3.6.2 The Angular Momentum Transfer Analysis Nine states, including the ground state, (see Figure 3.13), with excitation below about 500 keV can be observed consistently across most of the spectra. Above about 500 keV of excitation the states observed in some of these spectra have become so crowded that no specific pattern can be readily observed. By rounding to the nearest 5 keV the nine states can be listed as: ground state, 50 keV, 160 keV, 240 keV, 275 keV, 330 keV, 400 keV, 450 keV, and 500 keV. For the spectra on four plates, taken at the scattering angles of 10°, 15°, 22°, and 27°, the reaction was the same, and the same target was used. In addition, the other experimental parameters involving equipment and the operation of the cyclotron were sufficiently consistent that the integrated charge collected by the Faraday cup in the bombardment chamber could be considered proportional to the target bombardment. 77 These four spectra are shown as the four right hand diagrams in Figure 3.13. The areas of the peaks for seven of the nine levels in these four spectra were measured on the stripped spectra and divided by the charge collected during that particular run. This gave a set of rela- tive cross-sections in arbitrary, but comparable units. The distorted wave spin orbit program DWUCK (KunP70) with the Fadner et a1. (FadW69) optical model parameters was used to calculate the theoretical cross section for the angular momentum transfers from 0 to 9 as a function of angle. Good experimental Optical model parameters for this reaction have not been reported in the literature. It was not the purpose of this study to find these values, so the parameters that were used did not necessarily lead to the right magnitudes for the R—transfers, but it is believed that they did preserve the angular dependent shape of the cross-section (HinR74). A plot of the cross-sections for each of the R—transfers was obtained from the computer. The experimental cross-sections for each of the seven levels was superimposed upon the theoretical cross-sections to find those for which a reasonable fit could be obtained. Fig. 3.14 shows those plots for the different levels for which a reasonable fit was observed. Table 3.4 summarizes the seven different states and those angular momentum transfer cross—sections for which a reasonable fit existed. The application of this information to the development of the energy level diagram will be the subject of part of Chapter V. SCATTEle CROSS 'SECTION (ARHTRARY UNITS) 160 keV GROUND STATE l llllHl 240 keV m w w SCATTERING ANGLE (deg) 20 4o xnmmm mmm(mm ”8$n(3He.1)”SSb BEAM ENERGY = 32'40 MeV T 330 keV l r1’\411llul ._ ._ 4O SCATTERING ANGLE (dag) Fig. 3.!4 Theorectica/ cross—sections for different l—transfers compared with experimental cross—sections. TABLE 3.4 List of the Angular Momentum Transfers with Reasonable Fit Between Theory and Experiment State Observed in Possible the Spectrographic Angular Momentum Plate Data Transfers Ground state 0, 1, 2 50 keV 0, 1, 2 160 keV 4 240 keV 0, 4 275 keV 0, 2, 3, 4 330 keV 1, 2 400 keV O, 3 80 CHAPTER IV THE DECAY SCHEME AND LEVELS OF 11886 4.0 The Decay Scheme Figure 4.1 shows the decay scheme and levels of 1188b for the levels up to approximately 1200 keV. Each of the levels is labeled with its energy and uncertainty. The uncertainty in the energy of each of the gammas that depopulate each level is known. (Chapter III). The uncertainty in a level then, is the geometric average of the RMS uncertainties of all the gammas depopulating a level and the uncertainties of the lower levels fed by the same gammas (BevP69). The energy of each level is the weighted average of the energies of all of the gammas that depopulate a level and the energies of the lower levels fed by the gammas (Ibid.). In the following sections this level scheme will be built piece- meal using the most significant levels as a frame work. These are significant in the sense that the determination of their location and relationship to one another were crucial to the construction of the level diagram. The first sections will construct the portions of the level diagram that contain the most significant information; namely excitation information and coincidence data. Later sections will add corroborative data from energy differences and cross—over transitions. Figures showing those related parts of the level scheme which are ger- 81 .omm.. com Emtmm.m .m>m. kw me ow xmumcm mmtwmmmsm med .9 .9. Gama: 82 maine to the arguments and rationale will be used. It may be helpful to refer to Table 3.3 which is a listing of the coincidences observed for those gammas believed to belong to 1188b. 4.1 The 324.0 keV and Related Levels Figure 4.2 shows the 324.0 keV level and the gammas that are believed to feed directly to or from it. As discussed in Chapter III (§3.l.4) the threshold of the 324.2 keV gamma appears to be about 340 keV. For this reason this gamma is believed to go to the ground state. This establishes a level at about 324 keV. The thirteen gammas that observed in coincidence with the 324.2 keV gamma are believed to feed it directly are shown in figure 4.2. These same thirteen gammas are also found to be coincidence with one of the gammas of the 273 keV doublet. This,plus the fact that one member of this doublet also has a threshold of about 340 keg suggests that one of the components of this doublet decays from this same level to a level at about 51 keV. Since the two members of the 273 keV doublet were never precisely resolved, the energies could not be obtained directly. As will be developed (§4.3, and 4.4), six other gammas also appear to decay to this 51 keV level. From them, the energy of 50.8 keV has been assigned to this level. The difference in energy between the 324.0 keV level and the 50.8 keV level provides the energy of 273.2 keV for this member of the doublet. This compares favorably with the value of 273.3 keV as obtained from the best SAMPO data (§3.1.4). There seem to be no other gammas decaying from this 324.0 keV level. '% 6° 86321.1 730.913 (,9 4551. 6) 628.6 .2 'Lo 1““ N '——-/— -621 9° 59031.3 ’1 ex 9 1 1 y y '5" til 323.091 1 50.812 118 51 Sb 87 Fig. 4.2 Prominent feedings to the 324 keV /eve/. 84 4.2 The 165.7 keV and Related Levels Figure 4.3 shows the 165.7 keV level, the gammas that are impor- tant in establishing it and the energy levels related to those gammas. Coincidence experiments establish that the 317.9 keV gamma is in coincidence with the 456.1 and the 297.9 keV gammas. The 456.1 keV gamma, is also in coincidence with a 115.4 keV gamma,and the 297.9 keV gamma is also in coincidence with the 324.2 and the 273.2 keV gammas. By energy sums and/or differences this establishes a sequence of levels: a 938.2 keV level which decays, in part, by means of a 317.9 keV gamma to a 621.9 keV level. From this level the 297.9 keV transition popu— lates the 324.0 keV level and the 456.1 keV transition populates a 165.7 keV level. The 115.4 keV gamma seen in coincidence with both 317.9 and the 456.1 keV gamma has a threshold of around 170 keV (Section 3.1.2). This 115.4 keV gamma must then represent a transition from the 165.7 keV level to a level at about 50.3 keV. This is believed to be the same level as that fed by the 273.2 keV gamma (Section 4.1), and to which an energy of 50.8 keV has been assigned. In a like manner a 112.3 and a 488.7 keV gamma are both in coin— cidence with a 462.9 and a 304.5 keV gamma. The 462.9 keV gamma is also in coincidence with the 115.4 keV gamma and the 304.5 keV gamma is also in coincidence with the 324.2 and the 273.2 keV gammas. This establishes another cascade which pOpulates the 165.7 and the 324.0 keV 6\ 0° \ 1118 81-1 {,9 x N %0 '13 a?) 1018 8+ 7 \v 19 '5) 938.2i.1 .9 \ 6\ ’Jr 9 9 ’16) \Q’ (I; "0 °\ \\' Q) 91‘ \ 740.9353 (09‘ ’1 Q‘3J x) x {5 \Q; {r 9 6 q, .6359 69° 6’" 828 6:1 2 °‘ "' ’ 821.91.2— ~x\ '9 '1 \X‘ (be 6’” 1‘ 329.011 \ 699 \N g?“ 9 165.712 50 8+ 7 0.0 118 51 8b 87 Fig. 4.3 Prominent feeding to the I66 keV level. 86 levels: the 488.7 keV transition is from a 1116.8 keV level to a 628.6 keV level. The 112.3 keV transition is from a 740.9 keV level to the same 628.6 keV level. This level is then depopulated in part by the 462.9 keV gamma which goes to the 165.7 keV level and the 304.5 keV gamma which goes to the 324.0 keV level. A third cascade further identifies the 165.7 keV level: a 278.1 keV gamma is in coincidence with a 575.2, a 416.9, and the 112.3 keV gammas. The 575.2 keV gamma in turn is also in coincidence with the 115.4 keV gamma and the 416.9 is also in coincidence with the 324.2 keV gamma. This indicates that the 278.1 keV gamma is a transition from a 1018.8 keV level to the 740.9 keV level. This level is then depopulated by the 112.3 keV branch discussed before, a 575.2 keV transition to the 165.7 keV level and a 416.9 keV transition to the 324.0 keV level. It would be expected in cascades such as these that the first member should be seen in coincidence with the third, i.e. the 278.1 keV gamma should be seen in coincidence with the 115.4 keV gamma. In some cases it is. In many it is not simply because the intensities of one or more of the gammas involved is just too weak (see Table 3.1). 4.3 The 403.2 keV and Related Levels Figure 4.4 shows the 403.2 keV level, the gammas related to this level and other levels pertinent to this discussion. Placing the 403.2 keV level was important because the systematics of the feeding to and from this level helped to delineate the identity of the two components of the 237.2 keV and 238.5 keV doublet. 87 \ <51 ‘5’]? (o 1095.8+-9 :9 Q? 93):? r5 788.212 \ 9°? Q .511 \‘J 556.812 \ '1) 8‘ 83’ ,8 t» ’5" 19 L+03..2¢.1 €§ \ng 6‘." 8 185.712 50 8+ 9 0.0 118 51 Sb 8? Fig. 4.4 Prominent feedings f0 fhe 403 keV level. 88 These two peaks were never clearly resolved in any Spectra. However, by placing one coincidence gate on the lower half and another one on the upper half of this double peak, and using the same region for background subtraction it was possible to identify which gammas were in coincidence selectively with the 237.2 keV gamma and the 238.5 keV gamma. (See also Section 3.2.3, for a discussion of this coincidence technique, and Appendix II for the pertinent spectra.) The 237.2 keV gamma is in coincidence with the 115.4 keV gamma and also with a 153.7, a 384.9, and a 692.6 keV gamma. This establishes the levels at 1095.8, 788.2, and 556.8 keV which are depopulated by the 692.6, the 384.9, and the 153.7 keV gammas respectively. These gammas feed the 403.2 keV level which then decays via the 237u2 gamma to the 165.7 keV level. A gamma was observed in singles spectra with an energy of 352.6 keV. It was very weakly observed in the 384.9 keV gate coincidence spectra. This 352.6 keV gamma is just the sum of 237.2 and 115.4 keV. It could be the cross-over gamma between the 403.2 and the 50.8 keV levels, or a sum+peak of the two gammas. In either case it should then also be in coincidence with the 153.7 and the 692.6 keV gammas which are also believed to feed the 403.2 keV level. These coincidences were not observed. As seen in the singles spectrum from.which relative intensi— ties were tabulated (see Section 3.1, and Table 3.1) the relative intensities of the 384.9, the 153.7 and the 692.6 keV gammas were, respectively, 2.2, 1.8, and 2.1. Both of the latter two have intensities 89 less than that of the 384.9 keV gamma so coincidences would be harder to identify. The 692.6 keV gamma is a member of a five gamma multiplet (690, 690.3, 692.6, 694.3 and 697.0 keV) which were never fully re— solved. (There will be further discussion of this "family" of gammas in Section 4.8.4) The much weaker 153.7 keV gamma is adjacent to a much stronger gamma (or gammas) at 158 keV. (This later is discussed in Section 4.11.) For these reasons the fact that a coincidence between the 352.7 keV gamma and the 153.7 with the 692.6 gamma is not observed is not unreasonable. The question of the 352.6 keV gamma being a sum peak of the 237.2 and the 115.4 keV gammas can be examined by looking at the relative singles intensities. The relative intensities of the 115.4, the 237.2 and the 352.6 keV gammas were, respectively, 100, 19.7, and 2.6. The intensity of the 352.6 is 13% of that of the 237.2 keV gamma. This is much too high for it reasonably to be a sum peak. For these reasons the 352.6 keV gamma is included in the decay scheme. 4.4 Other Feedings Involving the 324 keV Level The 829.1, 806.9, 793.1, 771.8, and 694.3 keV gammas have already been discussed as being in coincidence with the 324.2 and the 273.2 keV gammas, and feeding the 324.0 keV level (Section 4.1). The levels that these gammas depopulate have been established at 1153.6, 1130.5, 1116.8, 1095.8, and 1018.8 keV respectively. These gammas and levels, and the other 90 gammas associated with this section are shown in Figure 4.5. Gammas of 1154.1, 1130.3, 1116.5, 1096.0, and 1019.1 were observed in the singles spectra. No coincidences were observed for any of these gammas. For this reason and because the energy of these gammas corresponds so closely to that of the levels shown in figure 4.5 it is considered, then, that these gammas probably represent transitions to ground from these levels. The following three sections will discuss several transitions which involve the 165.7 and the 50.8 keV levels as well as some other levels and ground. Figures 4.6, 4.7, and 4.8 will be referred to. 4.5 Several Feedings Involving the 166 and the 51 keV Levels For this section refer to Figure 4.6. The 878.1, 696.9, 575.2, 462.9, 456.1, and 374.5 keV gammas have been observed in coincidence with the 115.4 keV gamma which depopulates the 165.7 keV level. These gammas then establish energy levels at 1043.7, 863.2, 740.9, 628.6, 621.9, and 540.3 keV. Gammas of energy 1044.3, 863.3, 622.0, and 540.7 keV which are observed in singles spectra and whose energy error is within the limits of the corresponding energy of the level with that energy, are believed to depopulate these respective levels to ground. The difference between the two members of the following gamma pairs (690.3, 575.2), (577.9, 462.9), (571.2, 456.1 keV), is each within 91 é} \ @«Oégp 199) ’9 N) w 3 @0’6’8‘0' '96) {J ’19 of, x \‘L‘ 03‘ 1153.612 8 Q» Q} 4 00,6489 0) <9 1118851 9 Do—x . . x ’1 <55 (L—-————\1085.8i.2 \ %D «D Q3 to?) 1018.81'2 5b '9 e e r r ‘ i Q?” q, 32L1.0i.1 L 1 50.8102 l i i V ‘ ' ‘ 0'0 118 51 Sb 67 Fig. 4.5 Feedings involving fhe 324 keV level. 1083.713 88321.1 780.913 .Eill‘g ‘31\° :6%> 828.81-2 Q3“ \ 8——/—821.91—.2 ., .31 58031.3 185.7t.2 81.813 50.812 0.0 118 '51 8b 87 Fig. 4.6 Feedings involvmg ihe l66 and 5/ keV levels. 93 statistical uncertainty of 115.4 keV. The second member of each pair has been discussed as feeding to the 165.7 keV level, which is depopu— lated by the 115.4 keV gamma, feeding a 50.8 keV level. For this reason, and consistent with any coincidences that these gammas show, these gammas (690.3, 577.9, and 571.2 keV) are believed to feed from the 740.9, 628.6, and 621.9 keV levels, respectively, to the 50.8 keV level. One other gamma is shown in the figure, a 962.0 keV gamma which has no observed coincidences. The difference between the established 1043.7 keV level and an 81.6 keV level, is just 962.1 keV. This is within the uncertainty of measurement. For this reason, this gamma is placed as feeding from the 1043.7 to an 81.6 keV level. This 81.6 keV level will be considered in detail in Section 4.9. 4.6 Further Feedings Involving the 403, the 166, and/or the 51 keV Levels For this section refer to Figure 4.7. In this figure, four gammas of 994.0, 928.2, 832.5, and 772.5 keV are shown which are found in coincidence with the 115.4 keV gamma alone and therefore feed the 165.7 keV level. Thus the levels at energies 1159.7, 1093.9, are established by the first two gammas. The 832.5 keV gamma appears to depopulate a level at 998.1 keV and the 772.5 keV gamma appears to depopulate a level at 938.2 keV. These two levels were also established with decays to the 324.0 keV level by gammas of 674.0 and 94 \ 699 \\ <> 0\ <8)\' Q9. 9 \\ 1159.712 999’ 9.9 «51/ go «59$ 1083 8+3 '19 (0 Q“ 12” 4,9119 8,3) 1025.215 <2, <0 \5 \‘1' 998.1i.2 ’1’?) 061’ 1’1 8 83821.1 vb 6 .,\ 6"" 63’ 65' 9 9 $1 ’10 «O "b 1'5 ’52, 78821.2 \ Q) ’3’ \N‘ 83’ Q) '1 (Lo ll. 8" '1? L103711 32%.0i.1 Q\ 00 5° 6‘." \\ 185.7:t.2 50 8+ 2 0.0 118 51 Sb 87 Fig. 4.7 Feedings involving fne 403, I66, and 5/ keV levels. 95 614.2 keV respectively as shown also in figure 4.2 and discussed in Section 4.1. A gamma of 788.3 keV and one of 737.3 keV are observed in singles spectra but are not observed in coincidence. The differences between these two gammas is 51.0 keV. A 384.9 keV gamma discussed in Section 4.3 establishes a level at 788.2 keV. It is believed that these three gammas depopulate this level; the 788.3 keV gamma going to ground, the 737.3 keV gamma going to the 50.8 keV level and the 384.9 keV gamma going to the 403.2 keV level. 4.7 Feedings to the 741 and the 622 keV Levels Figure 4.8 shows these feedings. A 940.0 keV gamma seen in singles shows no coincidences. Also a 317.9 keV gamma in coincidence with a 456.1 keV gamma establishes a level at 940.0 keV. This latter feeding was discussed in Section 4.2. Apparently, the 940.0, and the 317.9 keV gammas depopulate the same level, the 940.0 keV gamma going to ground. A 473.8 gamma also in strong coincidence with the 456.1 keV gamma, and the 355.0 keV gamma, in strong coincidence with the 690.3 keV gamma must both depopulate the 1095.8 keV level. Other gammas which feed from this level were discussed in Sections 4.3 and 4.4. A 388.8 keV gamma is shown in figure 4.8 as being in coincidence with the 690.3 keV gamma. This gamma then, in conjunction with a 1130.3 96 ® 1130.512 '5 6' 1088 8+ 2 0 1018 8+ 9 980.012 <9 0 790.9133 891 9+ 7 \N 185.712 ‘50 8+? 0.0 118 51 Sb 87 Fig. 4.8 Feedings lo lne 74l and 622 keV levels. 97 and a 806 .9 keV gamma discussed in Section 4.4, defines the 1130.5 keV level. 4.8 Doublets and Other Multiplets 4.8.1 The 237, 238 keV Doublet The resolution of the 237-2 and 238.5 keV gamma doublet was discussed in Section 4.3. The energy and intensity of each member of this doublet were both resolved by the spectra analysis program SAMPO (op. cit.). 4.8.2 The 273, 274 keV Doublet The 273.2 and 273.9 keV doublet was partially discussed in Section 4.1. The 273.2 keV member of the doublet was used in the development of the decay scheme at that point. The 273.9 keV member will be dis- cussed further in Section 4.10. The presence of a very strong 270 keV peak, due to the 118Sn(p,y)1198b reaction, close to this doublet in the spectra, and the closeness of the two members of this doublet pre- cluded the precise measurement of the energies or the intensities of the two members by the analysis program. The energy of each member of the d oublet was obtained by calculating the difference between the two energy levels for which the gamma is a transition. The energy of each level in turn was obtained by finding the weighted average of the energy of all known gammas that populate or dep0pulate that level. The intensity of each member of the doublet can only be expressed 98 as being less than that of the unresolved doublet. 4.8.3 The 622 keV Doublet There is a doublet of about 622 keV. A 622 keV gamma appears in singles at an excitation of about 700 keV. Coincidence measurements show a strong coincidence with the 317.9 keV gamma which populates a level at 621.9 keV. The 622 keV gamma depopulating this level to ground and the 317.9 keV are shown in figures 4.3 and 4.6 and discussed in Section 4.2 and 4.5. There is however, an unmistakeable coincidence observed with a 622 keV gamma in the coincidence spectra of the 115.4 and of the 237.2 keV gammas. The 622 keV coincidence spectra also show strong coincidences with the 237.2 and the 115.4 gammas as well as with the aforementioned 317.9 keV gamma. It appears, then, that there is a 622 keV gamma feeding to the 403.2 keV level, as shown in figure 4.7. This gamma establishes a level at 1025 keV. It was not possible to resolve the 622 keV peak into its two com- ponents so the energy of each component and the relative intensities are not known. Since the analysis techniques (SAMPO) can resolve clean peaks in this range which are less than 1 keV apart it can be assumed that the two members of this doublet are Within 0.5 keV of the nominal value of 622.0 keV found for the composite. Since the coincidence spectra of both components show strong coin- cidences with the members of their respective cascades it can be argued that intensities of the two components are within an order of magnitude 99 of each other. 4.8.4 The 690-700 keV Multiplet In the energy region from 690 to 700 keV the spectra were very complicated. The ground state spin of 72Ge is 0+. The first excited state at 690 keV is also 0+. The transition between these states is highly converted and has a half life of 0.29 us. During the bombardment of the 118Sn targets, the neutron background produces a 72Ge(n,n') reaction in the detector. The conversion electrons from the deexcitation of the 690 keV level plus any nuclear recoil energy are "seen" by the detector as a 690 keV peak with a high energy tail. At the other end of this interval a strong gamma of 699.6 keV appears due to the 1;:Sn(p,y)1:?Sb reaction. Superimposed upon the Ge(n,n') tail were several gammas. The obvious changes in intensity that occurred with increased excitation energy and the observation of four definite coincidence groups in the coincidence spectra led to the identify of four gammas belonging to the excitation of 118Sb. With this knowledge and the fact that the gammas turned out to be about 2 keV separate from one another it was possible to use the analysis techniques (SAMPO) on many different spectra and obtain well delineated energies and intensities. The gammas found were 690.3, 692.6, 694.3, and 697.0 keV. Their coincidences and placement in the energy diagram have been discussed in Sections 4.1, 4.3, 4.4, and 4.5. Part of the point of this section is that though four definite 100 gammas were resolved from this group in the spectra, the difficulty of definitively separating this many overlapping gammas from one another does not preclude the possibility of there being other, unobserved gammas there. Also, there is a difficulty in finding the area under each peak and a precise centroid in a spectrum due to the uncertainty in the background subtraction. An allowance has been made for this in the expression for the uncertainties in the energies and in the stated intensities. 4.8.5 The 722 keV Doublet One other doublet was discovered in analysing the spectra. This was a 771.8, 772.5 keV doublet. The identification was made totally on the basis of coincidence information. The doublet was not resolved by the analytical tools. These two members are shown in figures 4.2 and 4.7 and their coincidences are discussed in Sections 4.1 and 4.6 because the doublet was not resolved and the energies of the component were obtained by energy differences as discussed in Section 4.8.1. The 771.8 keV gamma is one of five gammas which depopulate the 1095.8 keV level so the energy of this level is well defined. It popu— lates the 324.0 level whose energy has been established. Thus the energy difference defines the gamma. In a like manner the 772.5 keV is one of two gammas depopulating the 938.2 keV level, and populates the 165.7 keV level whose energy has been established. 101 4.9 The Isomeric Decay The lifetime experiments discussed in Chapter III, Section 3.4 ff showed a number of interesting relationships. The 115.4 keV gamma had two components; one prompt and one with a lifetime of 13.2 nsec. The 103.7, 187.7, and 238.5 keV gammas all showed lifetimes of 13.2 nsec. The 103.7 keV gamma shows a strong coincidence with the 115.4 keV gamma. (MSW73) Figure 4.9 shows the part of the decay scheme that is a consequence of this isomeric state of 13.2 nsec. Apparently the 103.7 keV gamma must feed the 165.7 keV level which is depopulted by the 115.4 keV gamma. All of the feedings to the 165.7 } keV level in the previous section are prompt and provide the prompt component of the 115.4 keV gamma. The feeding to this level by the de— layed 103.7 keV gamma provides the delayed component of the 115.4 keV gamma. This means that the level depopulated by the 103.7 keV gamma must have an energy of 269.4 keV. Other than the 115.4 keV gamma none of the other gammas observed in coincidence with the 103.7, 187.7, and 238.5 keV gammas had a measur— able lifetime. Also, other than the above mentioned coincidence between the 103.7 and the 115.4 keV gammas, and allowing for the large differ— ence among the intensities of these three gammas, they showed the same coincidences. Thus these three gammas must depopulate the same, 13.2 ns isomeric state at 269.4 keV. The 187.7 keV gamma must decay to a level at 81.6 ! 3' 102 19181+ 8 1072.512 1018.213 9§LL813 898 7+ 8 882.813 837.213 5889113 507.715 397.713 289.412 [13.2ns) 185.712 818+? Fig. 118 51 Sb 87 4.9 The isomeric sfafe, ifs decays and feedings. 30,313 0. 103 keV and the 238.5 keV gamma must decay to a level at 30.9 keV. Just as all attempts to find a gamma that could be dep0pulating the 50.8 keV level were unsuccessful, no gammas were found that could represent depopulation of the 81.6, or thefi30.9 keV levels. One of the factors that made it difficult to identify gamma rays at the energies of 30.9, 50.8, or 81.6 keV was that K x—rays fell on or near these energies. X-ray lines are broadened and it is difficult to identify weak gamma peaks in their vicinity. The sum of the prominent Kal and Kaz lines of Sn falls at 50.3 keV. The K82 lines of Sb and Sn are weak but they are at 30.4 and 29.1 keV, respectively. Since the targets were surrounded by lead and the entrance and exit ports of the bombardment chamber were also lined with lead a small intensity of Pb x-rays were always in evidence. The K81 and K82 lines occur at 84.8 and 87.3 keV. A search for gamma rays of 30.9, 50.8, and 81.6 keV was conducted using the x-ray detector (see Table 2.1, Appendix I) but no evidence of any was found. The maximum intensity discussed in Section 3.3 still provides the limit of observation. The rest of the gammas involved in coincidence with the 103.7, 187.7, 238.5 keV gammas must feed this isomeric state and they all fall into place readily, identifying the levels that they depopulate. Except for the 943.7 and 380.0 keV gammas which both apparently depopulate the 1213.1 keV level, all the other gammas depopulate a level singly and alone define a level and its energy. 104 4.10 The 273.9 keV Gamma Group The coincidence spectra quickly confirmed that the 324.2 and a 273 keV gamma depOpulate the same level. However, two gammas, of 232.8 and 293.8 keV, are observed in coincidence with the 273 keV gamma but not in coincidence with the 324.2 keV gamma. Moreover the intens- ity of the 273 keV gamma increased much more rapidly with the rise of excitation energy than the 324.2 keV gamma. This coincidence evidence plus the excitation evidence discussed in Section 3.1.3 strongly suggest that the 273 keV peak is a doublet. The second member makes its appearance known at about 700 keV. This provides an upper limit for its threshold. The energies of the two members of this doublet were obtained by differences, as explained in Section 4.8.2 as 273.9 and 273.2 keV. Neither the 232.8 or 293.8 keV gammas is ever intense enough at any of the excitation energies used to plot a curve of excitation and find a threshold. In addition an intense gamma of about 233 keV is seen in the spectra of the reaction 120Sn(p,nY)IZOSb. Very weak gammas of about 233 and 292 keV are seen in the 118Sb spectra at low excitat— ion energies and the intensity of neither one appeared to increase with excitation energy. The 233 keV gamma was essentially dismissed as due to the (p,nY) reaction on a small amount of 120Sn contaminant in the tar- get. The source of the 294 keV gamma was not identified. It was not un— til both the second and third coincidence spectra showed strong evidence of coincidence with part of the 273 doublet that interest in these two 105 gammas was rekindled. Two other gammas enter the picture. A weak 506.7 keV gamma is observed. It shows no coincidences. Its energy is just the sum of 273.9 and 232.8 keV. Its intensity is greater than that of the 232.8 keV gamma so it could not be a sum peak. Another weak gamma of 567.7 keV is also observed. It also shows no coincidences. Its energy is just the sum of 273.9 and 293.8 keV. The intensity of the 567.7 keV gamma is also too large to be a sum peak. It is believed that these five gammas form a group of levels which apparently do not feed into or out of any other levels of the level scheme. Figure 4.10a,b shows the two ways that these gammas can fit together consistent with the above arguments. Nothing in the coincidence data can tell which of the two possi— bilities is more likely. However, using the data from Figure 3.3 and the intensity figures it can be adjudged that since the intensity of the 273.9 keV gamma is approximately ten times the intensity of the 293.8 and 232.8 keV gammas that the decay must be as in Figure 4.10b. None of the experiments were capable of identifying the lowest level which was fed by the 273.9, 567,7 and 506.7 keV gammas. As discussed in the first paragraph the 273.9 keV gamma has appeared by 700 keV excitation. That means the lowest level could be anywhere below about 425 keV. It could even be any of the low lying states that have no observable gammas depopulating them. For this reason this group is set to one side in Figure 4.1 and the levels associated with this 106 mm 5 Q m m: mm B Q m m: j .3 .3 + m. a 3m .3 + Nam mum .0? .3 + N. H m.mmm 8.... mm. o .e .0 0, 0 o .o 8 oz xo xo /o .3 + mémdom a. 900 a . .3 + Nfimfiwm .9 .9 me .3 + N. « Numm A. re 3. a . z 00/ .9 39.8.2 o xv/o/o The 273 9 keV group. Fig. 4./0 107 partial level scheme are labelled, as in Figure 4.1 and 4.10 with an "+11", (e.g. 273.9 1 0.2 + LL). 4.11 The 158.3 keV Gamma A gamma of 158.3 keV shows up in the singles spectra. The excita- tion curve for this gamma is shown in figure 3.2. The data for this peak are less precise than for the other gammas but the character is clear. A gamma of this energy, or close to it, appears at sufficiently low excitation energies that it must be produced by a reaction other than 118Sn(p,ny)1188b. The subsequent shape of the excitation curve, however, strongly suggests the presence of such a gamma in the spectra of 1183b. There is a gamma of 158.5 keV which comes from the decay to ground of the lowest state in 117Sn. If any 117Sn existed as a contaminant in the 118Sn target, the reactions 117Sn(p,p')117*Sn, or 117Sn(p,ny)117Sb, could occur. The first reaction is the inelastic scattering. The Q value for the second reaction is —2.64 MeV. The Q value for the 118Sn(p,ny)1188b reaction is —4.478 MeV. Thus at any of the energies used in this study 117*Sn and/or 117Sb would have been produced if any 117Sn existed in the target. The half-life of the 1178b is 2.8 hrs. and decays to 117Sn. The intensity of the 158.5 keV gamma from the 117Sb decay is 3 orders of magnitude greater than any other gamma in that decay. Thus since even the intensity of the 158 keV gamma was weak, the identification of any other gammas from the same decay would have been difficult. Indeed, none were observed. The existence of the 158 keV 108 gamma in the spectra of residual activity taken after bombardment had ceased and decaying with approximately the right half-life gives further credence to the presence of a minute contaminant of 117Sn in the 118Sn target. The target used was borrowed from the Lawrence Radiation Laboratories, Berkeley, and no assay of its composition was available. The shape of the curve of excitation for the 158 keV gamma (Figure 3.2) shows a shape which is indicative of the presence of a gamma of this energy belonging to the deexcitation of 118*Sb. The difference between the energies of the 324.0 and the 165.7 keV levels is just 158.3 keV. (See figures 4.1 and 4.3). Eight pairs of gammas depOpulate higher levels and feed to the 324.0 and the 165.7 keV levels. This alone would indicate that a stop—over gamma between these two levels would be probable. If such a gamma did exist with a statis- cally identifiable intensity, it would be in coincidence with the same gammas that feed the 324.0 keV level. It should also be in coincidence with the 115.4 keV gamma which depopulates the 165.7 keV level. The spectrum of the coincidence gate of the 158.3 keV gamma shows the very weak presence of a possible coincidence with the 115.4 keV gamma. Spectra of coincidence gates for the nine gammas feeding the 324.0 keV level fail to show any evidence of coincidence with a 158 keV gamma. None of these gammas is very intense so coincidence with a weak 158.3 keV gamma would be difficult to identify. In spite of the lack of definite coincidence evidence it is believed 109 that the weak 158.3 keV gamma does represent the stop—over transition between the 324.0 keV level and the 165.7 keV level. A gamma of this energy is believed to belong to the deexcitation of 1183b. It does not show coincidence with any other gammas, therefore there is no evidence to identify this gamma as feeding to or out of any other state. It is, of course possible that there is an unidentified level above the 81.6, the 50.8, the 30.9, or above ground which is fed by the 158.3 keV gamma, but this is believed less likely than the aforementioned stop over. 4.12 Levels from the Plate Data Figure 3.13 shows the ladder diagrams of the energy levels from the data from the most meaningful seven spectra plates. The energy of each level is obtained from the centroid of each peak and the calibration curve for the parameters under which this data was taken. The analysis of these experiments was discussed in Section 3.6 ff. The precision of the stripping operation from which the centroids were obtained and the available statistics put a limit of about 130 keV for the placement of any level. The dashed lines indicate levels for which the statistics are very poor and whose position and existence is much less reliable. From these spectra certain specific conclusions can be drawn and other speculations made. The (3He,d) and (3He,t) data certainly indi- cate at least one level in the interval from 40 to 60 keV. This (these) probably correspond to one or more of the levels at 30.9, 50.8, or even the 81.6 keV seen in the (p,ny) data. The (”He,t) data indicate the llO weak possibility of a level in the 75 keV range. This may be the 81.6 keV level seen in the (p,ny) experiments. The small angle (10°), (3He,t) plate indicates a level at about 101 keV. The (3He,t) 15° plate showed a very weak level at 118 keV. Both of these spectra show a level at about 160 keV and another level at about 50 keV so the 101 and 118 are very probably the same level. This level could be the same as the 81.6 keV (p,ny) level. Because there is no other corroboration of this evidence in the other spectra the reliability of this level is low. For this reason it is not included in the level scheme. (Figure 4.1). There is definitely a level in the 160 to 175 keV range. All seven spectra show this. It is believed to correspond to the 165.7 keV leVel from the (p,nv) data. Five of the plate spectra show a level in the 230 to 240 keV range. This again is definite. No level from the (p,ny) spectra appears in this region. The energy is rounded to the nearest 10 keV and included in the level scheme. Five plate spectra show a strong peak in the region of 260 to 280 keV. From the (p,ny) spectra a level was deduced at 269.4 keV. They are probably the same. The 319 keV level seen in the (3He,t) plate taken at 10° probably corres— ponds to the 324.0 keV level from the (p,nY) data. The next group of levels from the plate data is harder to identify. All seven spectra show a level in the range from 330 to 370 keV. The lower one may be the same as the 324.0 from the (p,ny) data, but the next (p,nv) level that was found was at 397.8 keV. There is, then, lll apparently at least one level between the 324.0 and the 397.8 keV levels that is seen in the charged particle excitation, but not seen in the gamma deexcitation. The scatter of the energies for the level(s) from the plate data does not lend itself to a resolvable decision as to how many, nor where the level(s) should be, so none were placed in the level scheme in this region. The four (3He,t) plate spectra show a level in the range of 395 to 400 keV. These are probably the 397.7 and for the 403.2 keV levels seen from the (p,ny) data. A (”He,t), a (3He,d), and a (3He,t) plate spectra each show a level at 440 to 460 keV. The evidence is definitive enough so that a level at 450 1 30 keV is indicated in the spectra. From here on to the higher energies both in the levels from the plate spectra and the levels deduced from the (p,ny) data, the overlap between levels is such that no definitive statements can be made. Further interpretations of these plate data are relatively futile. 112 CHAPTER V THE PROPERTIES OF THE LEVELS OF 1;§Sb 5.0 The Overall Picture of the Odd-Odd Family of Antimony Isot0pes As was discussed before, no other experimental studies have been made that have led to direct information about the levels of 1188b. Also, no theoretical studies have been undertaken. The whole family of odd-odd antimony isotOpes is relatively virgin territory and a paucity of information exists about levels and spins, particularly 122 for nuclei lighter than 1223b. Elliot, at at. (E11D72), used a Sn (p,n) reaction to study the low—lying states of 122Sb and compared their results with (d,p) and (n,Y) reactions. They also cite the per- 1243b. 116 tinent references for Sb is under investigation at this writing (MorC74). This scarcity of data obviously means that experi— mental isotopic trends in this region are scarce at present. The antimony isotOpes are characterized by having one proton above the Z = 50 closed shell. The two levels closest to Z = 50 are the 2d5/2 116 level lies lowest for the isotopes Sb 5/2 through 120Sb, where the levels cross. For 122Sb and 124Sb the 1g7/2 and the 1g7/2. The 2d is the lowest level. 116Sb has 15 neutrons above the N = SOclosedefiuflJJ Itcan be assumed that the 2d5/2 and 1g7/2 states are essentially filled and for this, and the isotopes with N>64, it is only necessary to distribute (N—64)/2 pairs of neutrons among the states 2d3/2, 351/2, and 1h11/2' The odd neutron 113 then can be assumed to identify the neutron state. Table 5.1 shows the comparisons of the published spin and parity assignments for the ground state and some of the isomeric states for this family. 5.1 The Coupling and Configuration Possibilities for 118Sb It is certainly possible for collective motion to exist in this nucleus. It is also expected that configuration mixing will exist among the three neutrons beyond the filled 2d5/2 and lg7/2 states as well as between the neutrons and the single proton beyond the Z=50 closed shell. Thus a variety of interactions can be expected to affect the single particle states. Jackson et al. (JacA68) studied the spin and nuclear magnetic moment of the ground state of 118Sb using atomic beam magnetic-resonance methods. Their calculation of the nuclear magnetic moment using a single particle state for the proton and with the con- figuration of the neutron mixed among the 2d3/2, 331/2, and lhll/Z states agreed only poorly with the experimental value. Callaghan at al. (CalP74) studied the spin and nuclear magnetic moment of the 5.0 hr iso- meric state of 118138b using the technique of nuclear magnetic resonance of oriented nuclei. They added collective effects to configuration mixing in their calculation and assumed all three neutrons were in the lhll/Z shell. They obtained much better agreement (ut = 2.20 n.m. heor. vs u = 2.32 1 0.04 n.m.). exp. Both of these studies involved the ground states and the long lived 114 TABLE 5.1 Comparison of the Spin and Parity Assignments (JW) for the Odd—Odd Antimony Isotopes. Assignments in Parenthesis are Uncertain. (JacA68) Proton Neutron W Isotope t1/2 State State J 116 + + 116 - Sb m 60 min d5/2 h11/2 (8 ) 118 + 118m ' Sb 5.1 hr d5/2 h11/2 (8 ) 120 + Sb 16 min d5/2 d3/2 1 120 — Sb m 5.8 d3 d5/2 hll/Z (8 ) 122 — Sb 2.8 da 87/2 h11/2 2 122m - Sb 4.2 min g7/2 hll/Z (7 ) 124 — Sb 60 da 87/2 h11/2 3 115 isomeric states (where the odd neutron is lhll/Z) of 1183b and other higher A members of the odd—odd family, but no general theoretical studies have been done of the excited states of this odd—odd family even involving only simple shell model configurations. Careful exp— erimental studies of gamma ray angular distributions will have to be done before a positive beginning of the unraveling of the spin assign- ments can be made so it is impossible at this stage to identify any collective effects or even sort out the configuration mixing. As a consequence, this section and those that follow will concentrate on the simplest shell model, coupling, and configuration arguments. There is no way that all of the combinations and ramifications could be dis— cussed. With only one proton above the Z = 50 shell, the proton configur— ations of the states of 118 Sb should be somewhat simpler to determine than those for neutrons. Insight can be gained by using the odd—group concept (i.e., odd-proton, vs odd—neutron group) and using the Brennan and Bernstein modification of the Nordheim coupling rules (BrenM60). The odd—proton states can be determined by examining the neigh- boring odd-mass isotopes of Sb. These are shown in Figure 5.1. This indicates that for 1183b below 700 keV the most probable states avail- able are the TTZdS/2 and filg7/2. The next higher level at 'iTlhll/2 1S expected to be somewhat higher. It is expected that the TTZdS/2 state will strongly dominate near the ground. The odd-neutron states can be determined by examining the neigh- boring odd—mass isotones of tin and tellurium. Those for which spin 116 2. a mm a 8 a 5.3 9.5 2.8 .1183 .NB .an S .3 / / 811.88 @8383 / / m8 n o i// m // nmoliéflue 85' $153 . ONNIIIII « co 9.3 ONb.llll .m +N\D oo. CON Don 000 com 00b (A9!) A983N3 Slafes for fhe odd-prolon componenfs of [/8Sb. Fig. 5./ 117 and parity assignments are known are shown in Figure 5.2. This ind— icates that in the region below 700 keV the states available for 118Sb are the 1/2+, 3/2+ and 11/2—. These are quite probably the V3sl/2, 02d3/2, and the Vlhll/2 states. All three of these states lie relativ— ely close to one another so competition amone them should be fairly high. This would indicate that the low levels of 1183b should be rath—' er complicated and admixed. Further evidence for competition is evid— enced by the fact that though Figure 5.2 shows the VSl/Z state lower 1188b is known to be 1+. This can than the Vd3/2. The ground state of only be accomplished by the coupling [(Wd5/2)(Vd3/2)]1+. Thus coupling between the proton and neutron states has resulted in an apparent cross— ing of the neutron states from that indicated by the odd—group concept alone which would yield [(fld5/2)(Vd1/2)]2+. The simplest configurations which are expected to contribute to the lowest states in 1188b are shown in Table 5.2. They are listed in the expected (rough) order of increasing energy for the proton state. The ordering of the three lowest neutron states is probably very mixed and may, for some configurations, be inverted. The predicted lowest lying states, those in the last two columns, were obtained by apply— ing the Brennan-Berstein coupling rules: The "strong" rule, R1; J = ljl - jzl for jl = £1 1 1/2 and j2 = K2 T 1/2 the "weak" rule, R2; l N H H- J = Ijl 1 j2| for jl - 1/2 and jz = £2 1 1/2 118 82.2 858 m: a... ON} ON: on. . «B \ 2.... o. \ \\ \ \\ com .an \ n.m. -~\__ 1 \ \ 81 on» $81. one .81. \ m: ow. 83 \ 3811.80.83 own I?N\0.N\nv om? Ilaomxnfixm. Ono bmuom.‘ 0N: 1N). AoN\: 00¢ 00m 000 CON (Ami) ASHSNE Fig. 5.2 Slaies for lne odd—neuiron componenis of [/8Sb. 119 TABLE 5.2 . 118 Possible Configurations for Low tying States in Sb Predicteda Lowest Proton Neutron Coupling Lying States State State States Produced Rule Particle— Particle— Particle Hole + + + + + d5/2 d3/2 1 ,2 ,3 ,4 R1 1 (ground state) sl/2 2+,3+ R2 3+ hll/2 3‘,4“,5‘,6‘,7',8‘ R2 8',3‘ (87,2)‘1 1+.2+.3+.4+.5+.6+ R3 5+ 015/2)“1 0+ 1+ 2+,3+,4+,5+ R3 4+ + + + + + + g7/2 d3/2 2 ,3 ,4 ,5 R2 2 ,5 (SI/2rl 3+,4+ R3 3+ 81/2 3+,4+ R1 3+ hll/2 i2‘,3‘,4‘,5‘,6‘,7‘, R1 2' 58-,9- 1 —1 1 (87/2) !0+:1+92+93+34+35+9 R3 6+ 6+ 7 ’ (d5/2)-1 1+,2+,3+,4+,5+,6+ R3 5+ Less probable: + + + 81/2 d3/2 1 ,2 R1 1 -1 (SI/2) 0+,1+ R3 0+ 81/2 0+,1+ R2 1+ _1 _ _ _ (g7/2) 3 ,4 R3 3 _. + Table 5.2 (Contd.) 120 / h11/2 d3/2 4 ,5 ,6 ,7 R1 4 -1 _ _ _ 81/2 5_,6_ R2 6— + + + + + + h 0 1 2 3 4 5 1 2 a 9 3 a 3 1 / 6+,7+,8+,9+,10+, 11+ (g7/2)—1 2:93:’4_,5—)6-,7—9 R3 8— 8 ,9 -1 _ _ _ (dS/Z) 3 4 ,5 ,6 ,7 ,8 R3 7 3Using Brennan and Bernstein's rules R1 and R2 for particle—particle coupling, and R3 for particle—hole coupling. 121 and the particle-hole "weak" rule, R3, which is much less reliable: J=jl+j2-1 The fourth column of Table 5.2 lists which of the coupling rules is applicable. The effect of these rules will be discussed later. There are still other configuration arguments that are applic— able. The single proton above the Z = 50 closed shell undoubtedly can be assigned the Nd shell for the ground state or the fig7/2 shell as 5/2 the first excited state (PreM62)(JacA68)(CalP74). The configuration for at least three of the seventeen neutrons above the N = 50 closed shell is not so clear. As discussed in Section 5.0, the v2d and 5/2 V1g7/2 shells are essentially filled with six and eight neutrons, res— pectively. The remaining three neutrons are somehow distributed among 3/2 and vlhll/Z shells. The neutron configurations for either the ground state or any of the excited states most probably con— sists of a pair plus an unpaired neutron in some one of the possible combinations. The odd neutron then identifies the state configuration. Table 5.3 shows some of the possible configurations. The identified ground state configuration for 117Sn is shown for comparison. As was stated for Table 5.2, this table does not attempt to order the neutron configurations by energy. They are probably very mixed and even per- muted. As can be seen, there are three configurations formed with a j = 3/2+, two with a j = 1/2+ or (1/2'1')-1 and three with a j = 11/2_ neutron state. In addition, there is the mixed state with one neutron in each configuration and two configurations which would be hole states by the excitation of a neutron from the Vd5/2 or Vg7/2 level. There is 122 TABLE 5.3 Some Possible Neutron Configurations for Ground and Excited States of 118Sb. Not Listed in Order of Energy(a) Possible Neutron Configuration Neutron State 2d5/2 1g7/2 2d3/2 3S1/2 1h11/2 1%33n67 6 8 0 1 2 j = 1/2+(b) 1%?Sb67 6 8 1 2 0 j = 3/2+(C) 1 0 2 j = 3/2+ 3 0 0 3/2+ (3/21”)‘1 1 1 1 0 1 2 1/2+ (1/2+)‘l 2 1 0 1/2+ (1/2”)‘1 0 2 1 11/2' 2 0 1 11/2‘ 0 0 3 11/2‘ 6 7 2 2 0 (70+)"1 5 8 2 2 0 (5/2“)‘1 (8)0rdering of the last three states in not certain. Ordering apparent— 117Sn 118S ly changes from to b. See (EllD72) and ref (c). (b)Ground state from single particle configuration (PreM62). (C)Reconfiguration mixing appears to be quite appreciable. Ground state probably would be some combination of the first three conf- igurations (PreM62)(JacA68). 123 evidence to indicate the possibility of the latter. The possible 5/2+ 115Cd and five levels of 117Sn, and two assignment for three levels of 117 7/2+ levels of Sn could be formed by such an excitation.(LedC67) (CohB71). Consider further the ground state of 1183b and its possible re- configurations. This state very likely consists of a 1Td5/2 proton and a Vd3/2 neutron with a neutron pair in either the Vd3/2, vsl/Z’ or vhll/Z shells. Because these three shells all lie very close to one another in energy it is not only probable that the ground state wave function is a mixture of these paired configurations, but there is evidence to suggest that it is indeed true. (BreM62)(JacA68). The ground state wave function would consist of a linear combination of three terms: [(fldS/Z){v(d3/2)(d3/2)2}]1+, [(fld5/2){V(d3/2)(SI/2)2}]1+, and [(fld5/2){v(d3/2)(h11/2)2}]1+. A term with a split pair involving a vd3/2, Vs and/or Vhll/Z would not be possible so the wave fun- 1/2’ ction would contain only those three terms. Three states would then be formed, each with the same total angular momentum and differing slight- ly in energy. The lowest of these would be the ground state and the other two, with the same J”, would probably be close in energy. The closeness of these neutron levels in energy is suggested in 117 119 Sn and Te; and by two 119 Figure 5.2 by the 3/2 and 11/2 states for other pieces of evidence. The 3/2 state in Sn (with two more inter- 117 acting neutrons than Sn) is at 24 keV and the 11/2 level is at 89 keV. Also, as noted before, the 1/2 and 3/2 states have apparently crossed for 1188b from what would be predicted by the odd—group concept 124 alone. Where the neutron(s) has no (essentially) residual interaction with an odd proton, this effect is not expected to be observed until 121Sn. 50 Table 5.3 shows some of the other simple configurations that are possible with the three neutrons which are outside a closed shell, leading to different neutron states. If these, like the ground state, form levels by reconfiguration mixing with the proton states, the num- ber of possible states of 11 Sb becomes large. If recoupling and core couplings are also considered, the number of possibilities becomes very large, indeed. As a single example of reconfiguration, 117Sn shows five levels between 1.03 and 1.67 MeV with a spin assignment of J = 5/2+. These levels are presumably produced by reconfigurations of the SQP (single quasi particle) (Vd5/2)—l state. In this same interval are two 7/2+ levels, presumably from the SQP (\)g7/2)_1 state (CohB71). Considering simple coupling alone, the neutron SQP states are the . —l —1 . . _ Vd3/2, VSl/Z’ Vhll/Z’ V(g7/2) , and v(d5/2) , listed in order of prob able increasing energy. The SQP proton states are just the orbits of the N = 5 shell, fidS/Z’ fig7/2, “SI/2’ fihll/Z’ and fld3/2. The low energy configurations of 1188b are the 25 possible combinations of these. By recoupling, each of these configurations gives terms with several dif— ferent angular momenta. Also, as above, the various terms of the same .fi . . . . . . J , mix by reconfiguration due to reSidual interactions. 125 5.1.1 Coupling Under the Brennan and Bernstein Rules. When Brennan and Bernstein examined the systematic evidence of their jj coupling model in odd-odd nuclei they observed several general trends which were applicable to excited and isomeric states (BrenM60). If these trends and rules are laid along side the decay scheme for ll88b certain generalities about some of the levels emerge. No hard conclusions can be drawn, but a certain degree of speculation can be made. In general, where the R1 coupling rule is applicable for the ground state, there is a large energy gap between the ground state and the first excited state produced by recoupling (BrenM60). That would + and the recoupled 2+, 3+, mean that the ground state would have JTr = 1 and 4+ would lie higher. Further, if the residual interaction between the proton and neutron is relatively small, the ordering of these re- coupled states would place the 4+ as the lowest with the 2+ and 3+ level higher still. If the residual interaction is not small then the order— ing would be uncertain. If the ordering for 1188b is by the R1 rule, the transition from the 4+ to ground (1+) would be an M3 transition, but the energy gap would probably be large enough so that no significant delay exists. Thus, within the limits of the decay scheme recoupling under the R1 rule of the [(Nd5/2)(vd3/2)] ground state configuration probably would not be observed unless the residual interactions were not insignificant. Whether this same energy gap argument can be applied elsewhere where R1 is applicable, as indicated in Table 5.2, such as a possible [(fig7/2)(Vh11/2)] recoupling, is not certain. If this is possible, 126 then the 2— state from this configuration may be seen, and the other negative parity states from recoupling would probably lie higher. Coupling under the R2 rule has some interesting possibilities. The pattern seems to suggest a competition between the two states of spin jl i jzl (BrenM60). This implies the formation of a closely spaced low lying doublet where the energy differences are only tens of kilovolts, at the most, with the other recoupled states at higher en— ergies. This means that under the R2 rule the [(Wd5/2)(vsl/2)]lconfigur- ation would produce a low lying, closely spaced 3+ and 2+ doublet. In addition the [(Wd5/2)(Vh11/2)_l] configuration would produce a 3+ level under the R3 rule. With reconfiguration there should be a number of closely spaced, low lying 2+ and 3+ levels. The [(fld5/2)(vhll/2)] configuration under the R2 rule indicates the existence of two competing, low lying 8_ and 3— states, with the other recoupled states lying higher. The identity of the known long— lived (5.1 hr) state had long been postulated as 8_ and now has been measured (CalP74). The present study did not identify this isomeric level but did ascertain that it apparently lies at an energy below 80 keV. The other, the 3_ member of this doublet, should be nearby in energy. It would unlikely be the 50.8 keV level, for reasons that will be brought out later, but it could be the 30.9 keV level, the 81.6 keV level, the 13.2 nsec level at 269.4 keV, or even the unobserved low— est level of the "residual" group which are set apart and on the left side of the energy level diagram (see Figure 4.1). Whatever level is the 3-, its decay to ground would be hindered, and if there were no in- 127 termediate state between it and ground it too would very likely be an isomeric state. If there were an intermediate state and it was a (Vd3/2) or a possible (Vsl/z), transitions to it would also be unfavor- ed since AK.Z 3 and AJ.Z 4. Some of the other possibilities under the R2 rule would be the [(fig7/2)(Vd3/2)] configuration. The two competing states here would be the 2+ and 5+. These two would be close together, but not necessar— ily higher than the two configurations discussed above. Transistions between these two states would be unfavored (AJ = 3), as would trans- itions between the 5+ and the other states so far discussed (AJ.Z 2). The other states of this configuration would lie higher. Again, recon— figuration of the (Vd3/2) would lead to a number of possible levels. A group of negative parity states would also be produced by the [(Wg7/2)(Vh11/2)] configuration. This configuration would tend to follow the R1 coupling rules which would place the 2' state at the lowest level with the higher spin states at higher energies. The closest identified parallel is from the decay scheme of 122Sb. This isotope has a ground state with the configuration of [(ng7/2)(vh11/2)]. The Spin and parity of the ground state have been given as J1T = 2_, (LedC67d). There is a 4.2 min isomeric state at 162 keV which has been given a tentative assignment of J1T = 8' by Lederer. Jackson et.al. (JacA68) show a tentative assignment of JTr = 7'. The strict application of the R2 rule applied to the recoupling of the ground state, on the other hand, would suggest the second member of the doublet would be the J1T = 9-, with other states at higher energies. 122 There are two other isomeric states of Sb for which assignments have 128 been made. There is a JTr = 5+ (0.53 msec) state at 136 keV and a 1T J = 3+ (1.8 usec) state at 61 keV. The recognition of these other states will be used in a subsequent paragraph. At least some of the [(fld5/2)(Vg7/2)‘1] and [(fid5/2)(Vd5/2)-1] states would be expected to lie within the realm of levels seen in this study. As noted in Section 5.1, probable reconfigurations of (\)d5/2)_1 and (Vg7/2)_1 have been observed. If the (fld3/2) is coupled to these neutron configurations, states of 4+ and 5+ would probably lie lowest with other recouplings higher. With the (fig7/2) proton coupled to these (Vd5/2)-1 or (\)g7/2)_1 neutron configurations, states of 5+ and 6+ would lie lowest with other couplings higher. 5.2 Discussion of the Three Decay Groups of 118Sb. As seen in Figure 4.1, and noted in subsequent discussions, there are three distinct decay groups observed in the deexcitation of Sb. It would be very tempting to try to promote the association of each of these groups with definite configurations of the protons and/or neut— rons. Without experimental evidence thereto, such speculation contrib— utes little, so I will try to make only general suggestions. Since the depOpulation of levels that are associated with each group was not observed to be by transitions to levels of any other group (with the exception of the single transition from the 13.2 nsec 269.4 keV level to the 165.7 keV level via a 103.7 keV gamma) there must be something unique about the configuratirmks)of the protons and/or neutrons in each group that makes such "cross" transitions unlikely. 129 This would tend to indicate that the differences among these three groups involve major readjustments of the configurations of the pro- tons or neutrons or both. Any change of state produced by single particle changes in the proton configuration among the three lowest states would be from, or to a (fidS/Z), (Ng7/2), or (Wsl/z) configuration. Each of which would be hindered because it involves a AK.Z 2. Any change of state produced by single particle changes of a neutron among the three lowest states would be from,or to a (Vd3/2), (Vsl/Z), or (Vhll/Z) configuration and, again, each would be hindered because it involves a A£_Z 2. Thus these separate groups could be characterized by having a proton and/or a neu- tron in a particular single particle state, and transitions within the group, then, could be attributable to the other processes that have been discussed. Some reconfigurations that involve the breaking of one and the for— mation of a different neutron pair would tend to be hindered, so it is possible that each of the three groups could be characterized by a con— figuration that involves two of the three neutrons beyond a closed shell forming a particularily stable neutron pair. For example, a (vh11/2)2 pair would be one that is particularily stable. States which have such a pair in their configuration tend to be lower in energy than otherwise would be expected. Some of the possibilities are shown in Table 5.3. Of the other interaction mechanisms that have been described and are certainly part of the conditions which define the different energy 130 states, none would be a likely candidate for describing why there is the distinct separation of these three groups——at energies examined in this thesis. I believe the most probable mechanism is the first one mentioned, that each of the three groups is characterized by a specific proton state: (NdS/Z), or (flg7/2), etc., and/or a specific neutron state like (vd3/2); or by a pair of neutron states relatively close in K-value, e.g., (vdB/z) and (Vsl/Z), and (vhll/Z) and (Vg7/2)“1. Changes in levels within each group are characterized by recoupling, configuration mixing and reconfiguration, and/or collective effects (core coupling). Certainly as you get higher and higher in energy this idea becomes less tenable and crossing would probably be seen, but it is possible at the energy levels seen in this work. The next section will consider these groups, though I will not try to specify what proton or neutron state(s) define each group. 5.2.1 The Residual Group of Levels. At the extreme left on the level scheme as shown in Figure 4.1 there is a lone group of levels and feeding gammas: five gammas which show no coincidence or transitions to any of the other levels. It is not known that the bottom level of this group is the ground level. The decays are shown going to ground only so as to represent the relation— ship and relative energies of the associated levels. Since the lowest level to which this set feeds is not known, the levels shown are listed as, q.v., 273.9 + LL. Since the positions and spin assignments of these levels is not known, about the only things that can be said about 131 their configuration and spin assignments are that all of the spins prob- ably lie within one or two units of each other and that the spins dif— fer sufficiently in some aspect of their nature from the rest of the levels such that there is no observable transitions to them. 5.2.2 The Main Group of Levels. The main group of levels of the decay scheme (right hand group in Figure 4.1) show no feeding to any of the levels that belong to the other two groups, with the exception of the 103.7 keV gamma feeding to the 165.7 keV level. The main body of levels feed predominantly the 324.0, 165.7, and 50.8 keV levels and to the ground state. Since most of the higher levels depopulate by means of more than one gamma and these multiple gammas generally feed to some one or more of these four levels, the spin assignments of these four levels is probably within 2 or 3 units of one another, at the most. Since many of the feedings are 1+ to ground, which has a spin and parity assignment of JTr = , this suggests that most of the levels have relatively low spin values. If the possible single particle states fitting these criteria are examined (Tables 5.2 and 5.3) it can be observed that there is no way that the number of levels seen can be created without requiring that many of them are due to recoupling, reconfiguration, core coupling, and/or combinations of these as well as the single particle processes alone. The probability of these other processes is seen to be increas— ingly important when the 324.0, 165.7 and 50.8 keV levels are consid— ' -3. _-__ .. M 132 ered. There are eight pairs of gammas which feed from higher—lying levels to the 324.0 and also to the 165.7 keV levels. Yet only a very weak 158.3 keV gamma that could be a transition between these two lev- els has been observed. The 324.0 keV level is depopulated by the 324.0 keV gamma which goes to ground and a 273.2 keV gamma which goes to the 50.8 keV level. The 165.7 keV level is depopulated by the single 115.4 keV gamma which goes to the 50.8 keV level. The pattern of these gammas and levels is most easily observed in Figures 4.3, 4.5 and 4.6. Further several levels have pairs of gammas which feed the 324.0 keV level and ground. The strong decay to ground of the 324.0 keV level would suggest that it might be due to a single neutron excitation or other type of reconfiguration and have a spin J = 1 or 2. Since the 165.7 keV level is only weakly fed from the 324.0 keV level, it probably has a spin of J = 3 or 4, so that these two levels differ by a spin of 2. In addition to the 115.4 keV gamma, six other gammas feed to the 50.8 keV level. The levels from which these gammas come also feed either the 165.7 keV level, or ground, or both. This strongly ind- icates that the spin assignment of this level is between the 1+ of the ground state and the 3 or 4 that has been suggested for the 165.7 keV level. This would indicate a spin assignment of 2, 3 or possibly 4 for the 50.8 keV level. 5.2.3 The Isomeric Decay Group of Levels. The center decay group (central group of Figure 4.1) has some very interesting features. All but the bottom three of the gammas feed al— 133 most directly down to the one, 269.4 keV level. This level is an iso- meric state with a half—life of 13.2 nsec and the bottom three gammas all feed from this level. The 269.4 keV level is the only isomeric state that was observed in this study though the 8_ with a 5.1 hr half— life is known and has been discussed (see Sections 1.2, 3.3, 5.1, 5.1.1). Other isomeric states are expected and even hinted at, as will be dev- elOped in the next section. It is the question of the configuration of this 269.4 keV level that dominates the consideration of this group. As has been discussed:h1general terms before, this level must be characterized by the configuration of a neutron and/or proton state such that the transition to a lower energy state is hindered by the re- quirement for a larger than usual change in total angular momentum, or— bital angular momentum, coupling, or reconfiguration. For simplicity it is tempting to look at the single particle states and pick out the (vhll/Z) as a likely candidate. It is certainly a possibility since a single particle transition from this neutron state to lower states such as the (Vsl/Z) (which is probably lower energy), or the ground state (vd3/2) would be hindered by the requirement that A£.Z 3, and Aj.2 4. Thusly any state formed with the (Vhll/Z) would likely be isomeric. As has been discussed in Section 5.1.1. the [(fld5/2)(vh11/2)] configuration would be expected to have a low-lying doublet of an 8— and a 3_ state. The 269.4 keV level could be the 3- member. Since there are at least three ways of forming the (vhll/Z) configuration and the number of ways of coupling this neutron state to the proton state (the most likely candidate of which is (fid3/2)) is large, the number of states that could be formed by these configurations is very _.-= -- -. z_'.. . . 134 large. Thus a number of levels could be formed. If the hypothesis of this configuration is pursued, the 269.4 keV level would be the lowest, or 3_ state, and the higher levels would be formed by various other configurations, as mentioned above. Since almost all of the higher levels feed directly to this level, the decay modes would be M1, E2, or perhaps M3 for the higher levels. Thus the assignments for the different levels seen would most probably be from J = 3‘ to J = 6' maximum. 2‘ would also be a possibility if the proton is in the (Wg7/2) state producing a [(fig7/2)(vh )] con- 11/2 figuration with all of its possible couplings and reconfigurations. The isomeric deexcitation of a state with such a configuration could be accomplished in a variety of ways, the conceptually simplest of which would be the single particle change of the neturon from (Vhll/Z) to (vsl/Z) with Aj = 5, AK = 5, or (Vhll/Z) to (vd3/2) with Aj = 4, AZ = 3. The change in total angular momentum, AJ, would de— pend upon the coupling and could be anything from AJ = O to AJ = 3. Another possibility for this isomeric state would be [(flg7/2)(VSl/2)], or even [(Wg7/2)(vd3/2)]. Deexcitation to lower en— ergy levels of the first example would be hindered by the requirement that the proton change from (fig7/2) to (NdS/z) requiring a AK = 2, or a neutron change, (vsl/Z) to (vd3/2), also requiring a AZ = 2. The AJ of this example would depend upon the coupling for either change. The deexcitation of the second example would be the one single particle process, requiring A2 = 2, and again, AJ would depend upon the coupling. The same possibilities for a variety of higher energy levels feeding to the isomeric state could be examined as was done for the (VhII/Z) dis— 135 cussed above. From Table 5.2, the [(fig7/2)(Vd3/2)] configuration would be expected to have a low lying doublet, one member of which is 2+ and the other 5+. Certainly the decay of the 5+ state would be hindered relative to the low—lying states that would be expected from other con- figurations of protons and neutrons, requiring a AJ.Z 2. Three gammas depOpulate the 13.2 nsec isomeric level at 269.4 keV. The 103.7 keV gamma goes to the 165.7 keV level. The 187.7 keV gamma goes to the 81.6 keV level, and the 238.5 keV gamma goes to the 30.9 keV level. These levels will be discussed separately in the next sec- tion. If, as in the previous discussion, the arguments are made, strict— ly from the naive, single particle estimates, certain suggestions can be made about the deexcitation of this isomeric state. Using the Weiss- kopf single particle estimates and the relationship th 0.693/T% = A Ziki (Xi = decay constant of i gamma) for the lifetime of the state, and (Niki)/(Ntkt) = branching ratio (for gammas) estimates of the most probable modes can be made (LedC67e). If the three transitions are all considered to be E2 then the calculated life— time is 16 nsec and the branching ratios are within a few percent of the experimentally observed values (see Table 3.1). If the three trans— itions are all considered to be M2 the calculated lifetime is 1100 nsec and the branching ratios, though in the right order, differ from the experimental values by about 25%. The only other combination that re— 136 asonablwaitst e experimental values is if the 238.5 and 103.7 keV gammas are E2 and the 187.7 keV gamma is M2. This lifetime calculates to be 19 nsec with branching ratios within 5% of the experimental values. Calculations where one or more of the decays is considered to have a multipolarity beyond quadrupole lead to results that differ from experiment by several orders of magnitude. Since isomeric decays, particularily for E1, E2, M1 and M2 may vary from the Weisskopf estimates by several orders of magnitude, these calculations must not be taken too rigorously. For instance 122Sb has a 61 keV E1 transition with a half—life of 1.8 Usec, and a 75 keV E2 transition with a half—life of 0.53 msec. 121$b has a 507 keV (93%) M1 transition with a half—life of 2 psec. 122Te has a 564 keV E2 tran— sition with a half—life of 8 psec. Generally there is better agreement between experiment and theory for multipolarities beyond quadrupole, so a conservative hypothesis would be that the decay of this isomeric state is El, E2, M1 and/or M2, or the equivalent. 5.2.4 The 81.6, 50.8 and 30.9 keV Levels. These three levels are fed from above, but no feedings from them to any other lower level was observed. In Section 5.2.2 it was suggested that a spin assignment of J = 2, 3 or maybe 4 is probable for the 50.8 keV level. The 81.6 and 30.9 keV levels are fed from the 13.2 nsec isomeric state by what is probably a dipole or quadrupole transition. If, pure— ly for the purpose of generating a hypothesis, the isomeric state is assumed to be the 3- state (see Section 5.2.3), the transition to the 137 lower states is M2 or E1, then the assignments of these two states would be J = 1, 2, 4, or 5. Consider the two higher spin suggestions first. With a ground state of J = 1+, an assignment of 4 or 5 to the 30.9 keV level would mean a state with an appreciable lifetime. The Weisskopf single part— icle transmission estimate for the half—life of such a state would be about 100 sec for an M3 transition to approximately 107 sec for an E4 transition. Even if the single particle estimates are in appreciable *118 118 , error, the decay of Sb to the levels of Sn has been extenSively studied and no such long—lived transitions have been reported (BolH6l) (HatJ70). Thus a J = 4, or 5 is improbable for the 30.9 keV level. Since there are two other levels below the 81.6 keV level, neither of whose spin assignments is known, no meaningful suggestions can be made about the Spin of this level. Any of the four suggested values could be true. The most important consideration about these levels is that no feedings from them were observed. Two reasons can be advanced for this. One is that observations of gammas of these particular energies were difficult to observe. More on this later. The second is that the levels were sufficiently converted that the gamma intensity was below the threshold for observation. I shall discuss the 50.8 keV level specifically, as an example. If, due to single particle considerations, or their equivalent con— figuration or coupling changes, the transition from the 50.8 keV level is primarily E2, the conversion coefficients are “T = GK + aL = 17 + 0.8. 138 This means that only about one out of every eighteen deexcitations will be accompanied by a gamma ray--which could be observed. Strangely, the single spectra showed no gamma of this energy with an intensity sufficient to distinguish it from the high background in this region of the spectra. However, the spectra taken during the 33 nsec timing experiment do show a weak gamma ray of just this energy (see Figure 2.1 and 2.4). The intensity of the 50 keV gamma in the prompt band is down about one order of magnitude from that of the 238.5 keV gamma, which is one of those that deexcite the 13.2 nsec isomeric state (see Figure 3.11). [hi examination of the timing spectra compared to the regular singles spectra shows that the ratio of peak to background is substantially enhanced in the timing spectra. So, a weak 50 keV gamma is there, strongly suggesting that this state is appreciably converted. The 50 keV gamma has a half-life greater than 300 nsec. No attempt was made to measure this half—life more exactly since the timing exper- iment could not be expanded that far. This suggests that the 50.8 keV level is an isomeric state. Certainly others than the 5.1 hr (8_) and the 13.2 nsec have been predicted. A half—life of over 300 nsec to low nsec is not inconsistent with the discussion of the previous sec- tion and the assumption that this transition is an equivalent E2. If the half—life were very much longer than that it would indicate a high— er spin state than has been considered reasonable for this state. Even if conversion were not considered, deexcitation of the 81.6 keV and 30.9 keV levels would be hard to observe. The 81.6 keV level is only weakly populated. It is fed only by a weak 187.7 keV gamma. An 81.6 keV gamma would be right in the middle of the Pb X—rays, which are always very prominent in any spectra because of the shielding in 139 the experimental environment (see Section 4.9). If the 50 keV gamma was not seen in the singles spectra, a weak 81.6 keV gamma would be certainly invisible, and if a transition from this level to ground were at all converted, as well, the fewer gammas produced would never be ob- served. Transitions from this level could also take place by deexcitat- ion to the 50.8 keV level with a 30.8 keV gamma, or to the 30.9 keV level with a 50.7 keV gamma. This 50.7 keV gamma could be the same as the 50.8 keV gamma discussed above and will be reconsidered in the next section. A 30.8 keV gamma would be hard to distinguish from any that might be due to depopulation of the 30.9 keV level. Any depopulation of that 30.9 keV level by gammas would be hard to detect because this energy is on the edge of the overlapping peaks of the Sb X—rays. The intensity of gammas depopulating the 30.9 keV level would be less than that of 50.8 keV gammas depOpulating the 50.8 keV level considering the intensities of the feedings to the two states. If both are converted and the 50 keV gamma was not observed in the singles spectra, then cer- tainly a 30.9 keV gamma, in with the Sb X—rays, would be very hard to detect. 5.2.5 The Anomaly of the 30.9, 81.6 and 165.7 keV Levels. The 81.6 and 30.9 keV levels were established because the 103.7 keV gamma comes from the depopulation of the 13.2 nsec level and shows a strong coincidence with a 115.4 keV gamma. (For discussion of the placement of these levels see Section 4.9). The 115.4 keV gamma shows two distinct half-lifes, one prompt and one of 13.2 nsec. For these reasons the 165.7 keV level shows feeding from the two different groups. 140 There is, however, an anomaly here. Within error, the difference be— tween the 81.6 and 30.9 keV levels is just the value of the 50.8 keV level, which is the one to which the 115.4 keV gamma feeds. This would suggest that some kind of rearrangement of the levels consistent with all of the parameters that restrict and define the levels in the first place, could be found that would reconcile this suspicious difference. A concerted effort was made to try to do so. The final, reluctant con- clusion was that either these levels apparently are as they have been constructed, or the 115.4 keV gamma is a doublet, one member of which is prompt and a much weaker memeber that is in coincidence with the 103.7 keV gamma and thusly shows the 13.2 nsec half-life. All discussion up to this point has assumed that there is but a single 115.4 keV gammatflunzdepopulates a 165.7 keV level, which is fed by gamma(s) with two different half—lifes. All attempts to find a sec- ond member, i.e., split the 115.4 keV peak in the spectra into a doub- let, failed. If there is a second member, the two are very close in energy as indicated by the narrowness of the peak, the symmetry of the peak, the failure of computer program SAMPO (MorC70) to resolve the peak into components and, most crucial, the failure to find any meaning- ful coincidence difference by splitting the peak (see Sections 2.1.2 and 4.8). If there is a second member, and the assumption is made that it is fed only by the 103.7 keV gamma, or vice-versa, then the intensity of this second memeber would be less than 6% as intense as the stronger member. This, by itself, would make the identification of such a gam- ma difficult unless the separation between the two members of the dou— blet was at least 0.5 keV. If the 115.4 keV peak in the spectra is, indeed, a doublet with a 141 second, low intensity member that is in coincidence with the 103.7 keV gamma, what effect will this have on the decay scheme? The 13.2 nsec level was set at 269.4 keV by the requirment that the 103.7 keV gamma, which depopulates this level, feeds to the 165.7 keV level, since it is in coincidence with a 115.4 keV gamma which depopulates the 165.7 keV level. Without this requirement there is no reason for the isom— eric level being just where it is. This isomeric level is depopulated by a 238.5 keV gamma which is known to exist at an excitation of about 290 keV above threshold which puts an upper limit on where this level it. The simplest assumption would be that the 238.5 keV gamma feeds to ground. This would be consistent with the excitation requirement and also, goes along with the simple assumption that the isomeric level could be the 3— state, with the possible multipolarity of this trans— ition. So, if this assumption is followed through, the isomeric state is placed at 238.5 keV and the 187.7 and 103.7 keV gammas, which also depopulate this state feed down to levels at 50.7 and 134.8 keV, res- pectively. Within error, the 50.7 is just the 50.8 keV level, and "new" 115.4 keV gamma is in coincidence will be so—called. Since the with the 103.7 keV gamma, this will establish a new level at 19.9 keV. Figure 5.3 show these "new" levels feeding from the isomeric state, along with the "original" 115.4 keV gamma feeding from the 165.7 keV level. It is not shown in the figure but it would be just as likely that the "new" 115.4 keV gamma preceded the 103.7 keV gamma. This would lead to a level at 123.1 keV instead of at 134.8 keV, as is shown, as well as reversing the order of these two gammas. A different kind of evidence for this alternate level scheme would be provided if any gammas were observed in the data that could 142 13-2ns ‘1?) :8? \0 238.5 '\'\ 165-7 \'\ 134-8 1 y 50-7 1 19.9 Fig. 5.3 An alfernafe level for fhe isomeric sfafe. 143 represent transitions between any of these levels, or to ground. By taking all of the energy level differences, the possible gammas could be listed and searched for. Table 3.1 lists all of the gammas which * are believed to belong to Sb. None of these gammas fit the energy differences. If this alternate level scheme is right, then what was the 269.4 keV isomeric level drops down by 30.9 keV and becomes a 238.5 keV level. This would mean that all of the levels above this one in the isomeric group would also be 30.9 keV lower in energy than they are shown in the decay scheme (see Figure 4.1). There is that possibility that the 115.4 keV peak in the spectra is a doublet. This study, however, found no evidence to support the hypothesis and in the face of that, the decay scheme present in Figure 4.1 and developed in this thesis is believed to be most probable. 11 5.3 The 118Sn(3He,t) 8Sb Data. 118 The ground state of Sn had an assignment of J = 0+. In the (3He,t) reaction the total angular momentum that will be transferred 118 . to the Sb nucleus Will be (Z i j3 : jt)h = (Z i a i %)B = [2 + (0, +1, —1)]fi He where K is the orbital angular momentum that is transferred in the reaction. If Z is even there is no parity change, and if K is odd there is a parity change. If this information is added to that ob— tained from the angular distribution cross—sections, some broad conclu— sions can be reached. Only the four experimental point, at four angles, 144 either had sufficient statistics to give good readings or were suffic— iently resolved from the adjacent background and other overlapping peaks to provide the data to compare with the theoretical cross-sect- ions. In addition, the largest angle (center—of—mass) for which data were obtained was 27.70. Still, in all, these data were helpful. 5.3.1 The Ground State. The cross sections for the applicable orbital angular momentum transfers (in units of h) are shown in Figure 3.15. K—transfers of 0, 1, or 2 units are all reasonable though 0 and 2 have the best fits. An K- transfer of 1 unit, of course, would mean a parity change and would not occur since the ground state of 118Sb is known to be 1+. An K—transfer of either 0 or 2 units, i.e., (0 +1) or (2 — 1), could pro- duce the ground state. It is comforting to see the data converging this satisfactorily. It suggests a degree of reliablility for the higher energy states. 513.2 The 50 keV Peak. The 50 keV peak seen in the (3He,t) data is probably an unresolved combination of the 30.9, 50.8, and 81.6 keV levels. Since this peak on the plates was relatively well separated from the other peaks and showed no evidence of widening due to the mixing of significant con- tributions of the adjacent peaks, it would be reasonable to assume that the major contribution to this peak was the 50 keV level. As can be seen from Figure 3.15, orbital angular momentum trans— + fers of 0, 1, and 2 units are all equally reasonable. Thus J = 0, 1', 145 2:, or 3i are all possible. These values are consistent with the hyp- othesis that one or more of these three low levels are relatively low spin, but that the transition to ground is strongly inhibited by the complexity of the particle configuration and not due to the need for a large spin change. 5.3.3 The 160 keV Peak. The 160 keV peak is quite probably the 165.9 keV level. As is shown in Figure 3.15, the only orbital angular momentum transfer cross-section that is even close to fitting is for an Z—transfer of 4 units. Though the precision is poor this would suggest a J = 3+, 4+, or 5+ for this level. This is consistent with the discussion of Sect— ions 5.2, 5.2.2, and 5.2.4. 5.3.4 The 240 keV Peak. The 240 keV level is distinct, but was not observed in the gamma decay work. An orbital angular momentum transfer of either 0 or 4 units is seen in Figure 3.15 to be well fitted and equally reasonable for this level. This means that the level could have a J = 0+, 1+, 3+, 4 , + . or 5 . Without any gamma or other information very little more can be said. It was tempting to try to identify this level with the unobserv- ed 8- level. The angular momentum transfer data, however, preclude this possibility. 5.3.5 The 275 keV Peak. The 275 keV peak may be a combination of the 269.4 and 273.9 keV 146 levels. Since the true position of the level that is depopulated by the 273.9 keV gamma is not known and is designated as 273.9 + LL, (see Section 4.10) it is reasonable to assume that the 275 keV peak is es— sentially the 269.4 keV level. Figure 3.15 shows that an orbital ang— ular momentum transfer of 0, 2, 3 or less precisely, 4 units are pos— islbe for this peak. Thus J = 0, 1+, 2:, 3i, 4‘, or less possibly 4+, or 5+ are possible candidates. This level is the 13.2 nsec isomeric state and these candidates are all compatible with the discussion in Sections 5.2 and 5.2.3. 5.3.6 The 330 keV Peak. The 330 keV peak in the (3He,t) data quite probably is the 324.0 keV level seen in the gamma data. As Figure 3.15 shows orbital ang— ular momentum transfers of 1 or 2 units are both reasonable for this level. This means that an assignment of J = 0, 1i, 2:, Cr 3+ are all possible. Again this is consistent with the discussion in Sections 5.2 and 5.2.2. 5.3.7 The 400 keV Peak. This peak could be the unresolved 403.2 and 397.7 keV levels. As Figure 3.15 shows orbital angular momentum transfers of 0 and 4 units are reasonable and 3 is possible but less confident. This means that 1+ spin assignments of J = 0, , 3+, 4+, or 5+ are possible with a J = 2 3', or 4‘ less likely. 147 5.3.8 The (3He,t) Data Refined by Observations of the Gamma Decay. It would be very presumptuoustx)take the paucity of data and hard theory that is available and, from that, make suggestions as to spin assignments, but the exercise might be interesting. If the expectations of the spin assignments as seen in the gamma transitions between levels are superimposed upon the (3He,t) data some very naive and very tantative observations can be made. Since it is known that many of these transitions are complex. the use of simple single particle transition arguments will lead to condlusions that must be taken very lightly. Except for the deexcitation of the 13.2 nsec isomeric level at 269.4 keV, none of the other decays, from levels which appear in the (3He,t) data, appear to be delayed and, except for the very weak 158.3 keV gamma between the 324.0 and 165.7 keV levels, all of the gammas are fairly intense. With that in mind I am going to make some simplifying assumptions: all of the transistions involve AJ_Z 2, with AJ 2.1 more likely; that the 269.4 keV level is J = 3- as develOped in Section 5.2.3; and the weak 158.3 keV gamma is due to a spin change requirement of AJ.2 2. If I examine the levels involved with these requirments I find that almost any spin assignment that was found in the (3He,t) data could be applicable. That is, the 403.2 keV level could have spin J = 1, 2 or 3, the 397.7 keV level could have spin J = 1, 2, 3, 4 or 5, the 324.0 keV level could have spin J = 1, 2 or 3, the 165.7 keV level could have spin J = 3, 4 or 5, and the 50.8 keV level could have spin 148 J = 1, 2 or 3. Let me assume the even more conservative argument; that AJ 2 1, if not a better assumtion, is more likely for these transitions. The possible spin assignments, though certainly not more correct, do point out the expectation that these spins are close to one another. If I still require that J = 2 is the more likely for decays from the isomer— ic state and also the weak 158.3 keV gamma, then the possible spin assignments would be: (Figure 5.4 shows these more conservative assign— ments) the 403.2 keV level could have spin J = 2 or 3, the 397.7 keV level could have spin J = 2, 3 or 4, the 324.0 keV level could have spin J = 1 or 2, the 269.4 keV level was chosen to have spin J = 3', the 165.7 keV level could have spin J = 2 or 3, and the 50.8 keV level could have a spin J = 2 or 3. These might be considered a minimum or conservative set, indicat— ing, as was done many times in the preceding sections, how close to one another the spins of these levels probably are. 5.4 Recapitulation. There is no question that 1188b is a nucleus with very complex interaction among the nucleons that make up its structure. With three neutrons beyond the closed orbit and one proton beyond a closed shell the number of possible different configurations that can exist in the excited nucleus is extremely large. Precise gamma ray intensities and energies were measured for all gammas that were observed in the (p,ny) experiments. Excitation curves and thresholds were measured for sixteen of the more intense, low—lying \ Q) '1) 699 \\V (5% \" 9 a» 2 3 ,9. {$1 .é‘ l81321.1 2 3 L} N 1 397.713 03 '9 \ q“ 6’ (5° 1r2.3] é” a? e 321mm \ (,9 _ 65' [3 1 1 \ 26331.2 [13.2ns] o\ Q99 6‘?“ [3.3] Q 185.712 [2.3] so 8+ 7 L 0.0 118 SISb 87 Fig. 5.4 Tenfafive spin assignmenfs for some of the lower levels of ll85b. 150 gammas. Three (p,nyy) coincidence experiments were preformed to ident— ify those gammas which were in coincidence with one another. Many dif- ferent direct reaction experiments, the most important of which was (3He,t), at different angles,were carried out to try to identify dif- ferent nuclear energy levels and possible spin assignments. Experi- 118 ments were performed on the decay of Te to see if it fed any excited states of 1188b, particularily any isomeric states. An excitation threshold for the known 5.1 hr (8—) isomer was performed to see if its energy level could be identified, with possible feedings to that level. A search was made for isomeric states in the nsec range, and at least one was found. Seventy—five gammas have been assigned to the deexcitation of forty—one energy levels of this nucleus below an excitation energy of 1213 keV. These levels occured in three deexcitation groups with a small amount of mixing between only two of them. One isomeric state was discovered with a half—life of 13.2 nsec, another is suspected, a third is known from other experiments but not found in these experi— ments, and others are possible from theory. Many further experiments need to be performed. Certainly angular correlation studies to measure the Spin assignments of the states would have a high priority. I would not recommend that this be done by charge particle reactions of the (3He,t) type, or others like that. The cross-section for these reactions is extremely small, making the data collection, particularily at large angles, very, very ineffective. Experiments of beta-gamma coincidence need to be done. This would give access to the 8_ state and other possible isomers. Half—life experi- 151 ments in the u—sec range need to be done. Experiments should be done to study the three lowest levels, the 81.6, 50.8 and 30.9 keV levels, to find out just what is the deexcitation process of these levels. APPENDICES APPENDIX A The Ge(Li) Detectors That were used in this Study 152 >mx «.0 ® 233m o emuoc mamas: AOUOOV Sms Nmmz e swam o Acosmv >mx NNH e Exam Q amoa so 50 mm um AHHvaz SUGH mxm ou wmuwmaoo w m n >8 Beam Nav Ammmqv “mamam ommsxw umuuo .w H\¢N >mx m.H No.3 Hmwxmoo osuH Nmnlofi omuuo .m BowaHB mm as m~.o m>m wmm same as m Sn .amae as o fiAHAvaw Houumumw >mulx qqlm omuuo .o H\mm mo.N Nm.m Hmflxmoo msuH mqu mmUOHQ Hwoaosz .m H\om >ox H.N Nq.oH Hmflxmoo mSHH mqmq owOHD Hmoaosz .3 I I Nq.m m\oom mmfluumsvdH muumacmu .m H\NH >mx N.N Nm.N .xmoo Hmeaowmamua muons Hmmaosz .N H\w >ox q.m NN .xmoo HmwfiommamuH mmoOfiQ Homaosz .H coumEoo\xmmm oaOHuDHommm whosofloflmwm ma%H umusuomwacmz vaum mflfiu CH wow: mums umfiu muouoouma AflAvoo oSH H.< mamme < XHQmem¢ APPENDIX B All Pertinent Gates for the Coincidence Experiment at a Beam Energy of 5.37 MeV 153 mwmzaz szz3 m: m m _ _ .2 _ ____ 2; . 55 >2 mm .1. m m _ =:_ : E Z; : ____ NEE >3 mmm V m _ __ _ : __ 3 >9. smm n J EB >9. mmw m m 3 3 OH OH OH S S S. Omar seam mwmznz szz8; mmm ooom __ a __ =_ L‘ 119 _ _ _ _ memo >m; Tom L== 1728 8L2 memo >8; rmm Sq: ___ _ _fi_ _1=:L=__ 1708 862 Z 9 981 l. >ox 0mm _ _ _ xm memo >8; mam = = : _;£—fi=di=_ = _ 888 OH OH OH OH OH OH OH OH OH 155 mmmzaz JwZZ3 rum wh9. mm: wp8. mm: >3 0mm n wh9. mNm 156 one: mmmzzz szz0; 1mm 82 887 memo >mx mmm (8361H VV9 memo >8. 11mm >8; 0mm n xw 56 >8. mK OH OH OH OH OH APPENDIX C All Pertinent Gates for the Coincidence Experiment at a Beam Energy of 5.54 MeV 157 mmmznz 3mzz3 I: .1 :fl 2 .— _:a_____ €917 I wk3 N: . M_ __ i ,2. l 969 PC 8 CJ .10 /_ Z .V 669 , 8917 991/ Y 1 ES >3 m: . 1__ = 4.. __ __=qa 4a \. a: ‘__z___ =_ A _,. >3 93 n xm mbxw >0... mNH 158 000: ooom mwmzaz szz3 rm; _ _ MEG >3 we fig. 2: 2:443 g 1 = 22;: 3231—45; i wake >3 HRH >3 28 :_ :3: 1i 4:52:53: m “it; >3 m9 __;_= =.__§:_=I_< .: _ A _ ooofl : :. , :___ e _ E Z 8 ___ _ __ _:_ __=__ j l m A a OH OH OH OH 3 OH OH OH 3 mmeDZ mmzz3 mam __ A 3.1—2L:— mk3 mmm O 159 I ___ 22:; _d _:_:_= 1799 088 I791 wh3 mmm .2444: Ada—2:341 898 >3 m2: n xm mh3 mmm 160 mmmzzz meZ3 0km am 2:32: 4: 21.33.2311 1 ._ a: __ 4”,: :2 Q: 119 -- 862-7 882 912 1708 . - MEG >2 mxw _ : _> ___ _____=.___ 8L2 . me3 rmm -3 _ _ :. _ __ ______ :1: 8 Z .V v >3 93 u xm whxo >3 mmN le A 161 80.: ooom mmmzzz JmZZ3 Tom _ oooN 003 51:. E; _ ___ 119 1728 211 8L2 3 . mz.3 mHm Til—t 12:32. v . 9:6 >3 er 1r _. ___ _ ___ 3:: ___ ___:— 1: : ___ __ .0 ___—___: . >3 m2: u xm whxo >3 mmm 9917 ___. _ =____ 2.: 2 1708 862 912 OH OH OH OH OH 3 OH OH OH OH OH 162 mmm222 mwzz3 8m .1 _ _ _ = _ ___. __ _ __ =2 - mZo >3 {m . I I _ __ ,___: ___:= : _._;___=: 4 HEB >3 mmm _ _ ______1_ _ __ _ = ______o :5: >3 93 .I. xm “HP/mm. >3 m; 003 Co Z .V , 2 ___—2a _ 882 282 , 911 A A OH OH OH OH OH 3 OH OH OH OH 3 163 mmmzzz mwzz3 mm: m:.3 mm: >3 cm: >3 m2: n xm m._.3 mNm 164 ooor >3 mfiofi mmmzzz ooom oMWWzlon ”1:545 >3 mmm wH3 rmm m._.3 Km xw wk3 rmm oooH 3 OH S S S S 3 3 165 mwmzzz mwzz3 mmm woke >3 MS m:.3 NNm >3 £3 .1. xm wh3 rrw 166 ooor >3 93 n mwmzzz szz3 Hmm m._.3 mmm woke >3 Hmm xm wh3 mmm ooofi S S S S S 9 3 9 167 ooor >3 93 mwmzzz 4mzz3 mmm m._.3 mum wh3 on ooofl S 3 3 3 3 APPENDIX D All Pertinent Gates for the Coincidence Experiment at a Beam Energy of 5.82 MeV 168 mmmzzz szz3 :8 _ ______ ______ ___ __ =__ ___—5: , a _ Z_, ; j a 69 89V 99V VL8 V08 8L2 911 w._.3 N: V66 C._ L g 988 VL8 Co 8 821 V01 .7 9 Co 6'V69 99V PC mh3 m: . L _ 1_. ______:_______ 3a: V01 8 00 1L1 882 802 >3 oomH n xm mE.3 mNH . 1 I . ‘Ii :33! mmmzaz 4mzz3 :9 169 ___—___;_ ___________:__ I» 13.32;: 2 8 wk3 me m._.3 RH _ _ _ _:__ _ l T ,___.___1_ ____ __’._____E__:=__._ V99 988 VLS 821 >3 89 u xm wh3 mwfi m, N m 170 listiuuifi. I'I11 1 1 11 1111 1 11 1. . 1 1 1 c111 1111111 11111 mwmzzz mmzz3 mm“ 821 wp3 mom fi .2: ___. =2. __ ‘_ 19:9 >3 wHN _ _ ___ ___ __: ___. ___=_________.____ Z /_ PC >3 oomfi u xw ”:20 >3 mmm 9 O 3 9 171 ooor ooom mwmzsz szz3 mmN ___ ==Z= >3 oomH _ __ ___—___— .uEB >3 mmm = _: a _ _ _ wk3 omN u xw wh3 mmm __ E ___: (83611) 0901 oooN _ ___ ___—£1 ___—E 4: ___:J VV6 808 LVL 91L 269 oooH 229 V99 119 81V 088 898 988 1L1 911 821 172 mmmzzz DwZZ3 omm m>83 mmw __ _1>_= =__ ___ = =___= __ m>83 mum _ _ == __ =__ __; Z L >3 oomfi u xw w._.3 rmN mmmznz 4wzz3 mmN 1 J__Jmm_1_1dmd4fl-= = 68V 1 E5 >3 +18 M 3.: 3:52: 4:— mF3 gm 1 A = __ : _:_:_=___ _ /_ g /_ E Z 6 V08 862 912 >3 89 n xm mh3 er 174 mwmzzz szz3 mmm _ _ 2. fl _ : 31.2121: 33 >3 85 Z. 3 1:22: : MES >3 {m _ _ a _ __ ___: Z. ._ _:_ ___ 5.: ___ >3 8.04 u .3 ”its >3 8m 11..‘. 1 7w 8 8 911 175 89.. mmmzjz 4mzz3 mmm __ _ ::_:. 069 920 >3 omm _ _ _— _____ ___. . wh3 mo: _ ______::_ =__: _________:=__ =__ a >3 coma u xm mk3 9: Z Ce L : 2: 0H 3 3 o“ o“ 176 ooo L r I L ooom mh3 mm: _ LLfiALL wk3 mm: a: : La =L L L L LL =1 m>03 mm: LL LLL >w3 oomH u xm wh3 mm: mwmzzz szz3 :m L L LL =LL L mL13 mNm >3 oomL L La LLLw L L L E6 >3 mmm L L L1 _LJ a 6 E6 >3 Tom LLLLL a LLLL LL __LLLLL11_L LL 119 :LL PC 8 O 8L2 L L. _ L Z /L Cc V28 _ L _L_ L ELL._— 8 8 882 A A 3 0L 8 0L 3 0L OH OH OH S 3 OH mmmzLLZ uLmzz3 me 178 L L L L L L LLLL LLLL LLL LLLLLLLLE 898 911 E5 >3 mum L L I: LL LL LL LLLLLLLLLLLLLLLLLLLLLLLLLL E3 >38m L_ :L LLLLLLLLL LLLLLLLLLLLLLL V28 8L2 >3 oomH u xmL wh3 m5 179 mwmzzz qwzzwx NNm mho; rrw >0; coma n xm 180 ooo: mmmznz Luzz9. Hmw L _ 22% L. 2.1 :52: Co Z «V I m.L.9. mmw L L L _ L .L _L __L__L___43_L:L__ 9: HS 8L2 3% >3 m8 >9. coma L L L L dLLLLfi LLLLLLL‘L‘L 1:31.: 7v Co 8 ”EB >9. mK L 3 OH OH 3 181 ooo: >9. com. mmmznz IL ooom oonLZSLQ m.L.9. own m._.<0 >9. mrm m...9. mum wL.9. mmm ooo. o. 3 3 OH 3 S o. S 182 mwmzzz ILMZZ3 mom + w m L L L L LL L ___—L LL Lg - Eva >3 8m + w , ,, ; - L m m m L L L L L L :2: __L LLL—L :2: ___—LL LL r ”:6 >3 mmm - w m L L L L L L+ L fl L LL 1L L :LLLL_LL _ L Li:— - >9. 8m. u m. E6 >3 mrm L L m L o. 3 3 OH 9 S 3 mmmzzz ILmLZZ:me L , LL LL LLL LLLLL L LLLLLLLLLLLL mh9. mmm LLLLL L 3: LL _LL LLLL LLLL __LLLLLLLLLLLLLLLELLLLLL Z S 0 ES >395. LL LLLLL ALLLL‘LLLLL O m >9. com“ u xw w._.9. ommfi 119 ooo“ ELZ LL LL 9H S OH OH OH 3 S OH OH APPENDIX E Additional Spectra from Spectrographic Plate Data 184 Dom mmmzzz Lmzz0x OKH C AWE—HugwInwcmn: _ L “IBNNVHO 83d SiNflOC) com ownLnLLme omo< oor mmmznz ILmLzz