WW I l ‘WW I” “IN .A_ — 133 794 TH ' " Wp:-<‘-b. ng'a I’m. .‘ i -‘ , .’ i.) a .3 .. ° 1'6 #2:“: {3" v w [R a A v ,f‘ .. n ‘ ’3 u.‘ b . l j {a I g ' c 7., . ‘H. ‘\:... . .. V: _ t .' _I.§ I 4 : v. I ' ‘ .nub ! ..'.-n..-.\ .5 a ‘I b ‘M u\"‘ vv ‘ :Ia Ola "" . at“ V3.46 '* «_ n... . . I . ’ LII. o O "J - L—b- 1‘1;- . I..- \ . t 1111111111111111111111111111111111111111111111111111 31077090 9084 ' This is to certify that the 1 1 1 thesis entitled 1 : i 1 Desifln and Construction of 1 1 1 . a 50 K. v. X-Ray Unit 1 1 presented by ' 1 ' 1 Young C . Kim 1 x , 1 . - ' 1 ~ '. has been accepted towards fulfillment 1 ' of the requirements for , 1 - 1 . _M...S_c_ degree in_Eh¥8.;Lc S 1 ' 1 Major professor . a . Date May 17 , 1951 1», . 1‘ _ 1 .1' 0-159 1 ~ 1 ti"- _. . ” jg §; "f PLACEIN REI‘URN Box to remove this chedrout from your record. ;. u-ii‘i - ~ TOAVOID FINE return on or before date due. 1 - MAY BERECALLEDwith eanierdue date ifrequested. 1 DATE DUE DATE DUE DATE DUE l ‘ l V _ 1 ' v . , n ' i 1‘ . r ‘7 .fl .0 , -. I . - 1 . . -. ._I , A I‘ ‘ '. ' r .- ' ‘ ’ ‘ « A l _. ~ , - I . ._ ‘1‘ .,. . 1 14 .| 1‘ c . ». . . “‘. t . . ._ , r ‘ . u . l - , t u I ‘1' . < ' A \ . . v 1 ' _ ‘ ‘ o . ' .' v n ' . DESIGE AID CCISTRUCTI‘N CF A 50 KILCVOIT K-RAY ULIT by Young Chang Kim A Thesis Submitted to the School of G‘aduaue Studies of richigan State College of Agriculture and Agplied Science in partial fulfillment of the requirements for the degree of KASTER CF SCI‘ICE Department of Ehysics 1951 ACKK TLEDGEKEET I’would like to express my appreciation to Dr. homes H. sgood, Dr. R. D. Spence and Dr. J. C. Lee for their suggestions and help in accomplishment of this project. Bound 'C. Rim. I. II. III. IV. V. T '13 CF CCI TE; TS I TRCD”C”IO “ESIGN CF AkIARATUS a) High voltage su 33315 b) Rectii ication unit 0) K—ray filament circuit d) Lead box and x-ray tube e) Safety apparatus f) Spectrometer CPLRLTICK AI‘ IESTILG CF AEIARATUS a) Operation b) Testing and test ing data CCLCLCSICH REFLEEICES EASE F4 +4 14 11> to to N 15 16 18 18 ‘3 H I. ILTRCDUCTIOH This thesis reports the construction and testing of a 50 kilovolt x-ray unit and an associated Eragg spectrometer. It may be used for measurement of absorb— tion edges and for taking Laue and powder pictures, and is quite suitable for general use in any x—ray experi- ment requiring an x-ray source of medium intensity at a voltage not higher than 50 kilovolts. Since it em- bodies a water cooled tube, it can also be used for ex- periments uhich require long exposure times. The apparatus was constructed at low cost from surplus materials and other supplies available in the physics laboratory. This report gives a general descrip— tion and a detailed discussion of the required volta: supplies and the safety devices necessary to protect personnel against high voltage and harmful radiation. II. DESIGH CF AEEARATUS The main considerations in the design of the apparatus arise because of the restriction which the intended use of the apparatus places upon it. Since it was felt that it might be desirable to make measure- ments of a continuous x-ray spectrum, self-rectification could not be used. This implies the necessity of using some type of full wave rectifier. The ordinary kenetron capable of handling finverse voltages of 50 kilovolts or greater is large and rath r expensive. To obviate this difficulty small Kachlett rectifier diodes were used. Although these have a maximum inverse voltage rating of only 50 kilovolts, it was found possible to reach higher voltages by putting pairs of them in series. he Each— 1ett rectifier is about 6 inches high with its anode consisting of a heavy c0pper base about 2 inches high sealed to the glass envelOpe. The filament current re- quired for these tubes is a cut 20 amperes. In order to dissipate the large amount of heat develOped by such a filament current, the rectifiers must be cooled b; either water or forced air. In the present case it was impractical, because of the insulation problem, to cool the rectifiers by water. They were therefore mounted in a rectangular box through which a forced air flow wa maintained by a small notor driven blower. To provide the large filament f7 — L‘ - current for the hentrons it was necessa‘y to construct a filament transformer. In addition to the requirement that the filament transformer mLst be capable of deliver- ing the correct current, it was necessary that it be capable of standing the full voltage applied to the x-ray tube itself. This restriction can be understood from the fact that the x-ray tube which was used employed a water cooled anode. The positive side of the power supply was therefore at ground potential, and the negative side at about 50 kilovolts below ground potential. The fila- ment transformer consists of a rectangular yoke on which the primary 1. wound. The secondary 53 made in the form of a large circular coil and supported by g ass tubes in such a way as to provide a large air separation between the primary and secondary. The transformer for the unit was a Kelly Koett type JA special 90. The transformer was formerly part of a medical unit, and therefore was normally used to supply current only over rather limited intervals of time. The transformer was designed to supply about 114 kilovolts with a primary 210 volts. Despite the fact that the transformer was designed for only the intermittent use, it has given satisfactory service for rectified voltages of 50 kilovolts or less over a rather long period of testing. Another very important problem in designing any x-ray appa atus is the provision of proper safety devices -4- for the :ersonnel who may Operate the apparatus. These must protect personnel from radiation and prevent them from coming in contact with the Hi h voltages. To accomp— lisi the first objective the tube itself is Lounted in large lead box. The emitted beam is brought out throtgh a lead tube which collimates the radiation fairly well. To eliminate the danger of high voltages, the entire high voltage system is mounted behind a wire cage. Access to this cage, is afforded by a door to which is fastened a shorting bar and small contactor. Jhen the door is Opened, the bar connects the h'gh voltage terminal direct- ly to ground. At the same time the circuit through the contactor is broken and the supply voltage is turned off. Two remaining details of the 8:19? ratus should be nor ntioned at t :is point. The first is the control circuit for the system. It consists essentially of an autotransformer in the primary of the high voltage transformer. This control circuit consisting of the autctransformer and controlling accessories we Jart or the original redice 11 unit from which the high voltage transformer was taken. The x-rav tube has a water cooled molybdenum an dc. h is provided in the relay circuit to :3. h H (D U) u’) C. l 2' (D D P d- O the primary of the high vol age transforner, to protect the tube from having the beam turned on when the water is not flowing. The lesign details discussed in this section are “he n in Figs. 1, 2, S, 4, 5 and 6. Fig. 1 shows a schem- atic diagram of the wiring of the system with various elements of the system J beled in the attached list. Fig. 2 shows the wire cage containing the lead box with he controls for the s5rtem are at the L0 er ri ght. Fim 7 shows 1331 t o: the control systen for the x-ray tube filament, and the tOp of the high voltage transformer at the lower left. Fig. 4 and 5 shows the box containing the rectifiers. The secondary of the rectifier filament ransfor mer is visible below tr e box. Fig. 6 shows the x-ray tube as it is mounted inside the lead Lox. The leads to the right are the water connection. In the lower right one es s e the uressure switch. .L. Direc.cr5 for Diagram E.S.3.: Electric source switch board Switch for 115 VAC source Switch for 27 VAC source (Z¢) (for relay) Switch for 230 VAC source (l¢, grounded) LOUIE!) ['13 NH C.B.: Control board 1: Control rod for sw itch of raw filament circuit. 2: Control rod for rm jorr rheo a" circuit. of x-ray filam nt circuit. at of x- ray filament dt (>1 Control rod for minor rheos A.T.: Auto transformer A.T.S.: Auto transformer steps K.V.: Kilovolt meter T.S.: Transformer switch 8.1.: Relay for s: fety apparatus S.h.G.: Static high voltage shortening bar F.D.: Door of main :ge F.D.S.: Contactor switch of the door of main cage. L.: Lead box W.S.: Jater pressure switch X: K-ra; tube S.I.I.: Spar}: meter _ L.D.: Lead door for x-ray beam to spectrometer 0.8.: Switch to Open the lead door C.S.: switch to close the lee d door L.D.B.:battery for lead door K.T.: Tra sformer for Kcneti on filshents Kenetron tubes P l ow e r K. IX.I.: Transformer for x-ray filament C.: Iii :h volta ate cage A.: Anneter for filament current of x-ray tL be FS.: Switch for filament circuit of x-ray tube R.: 1.251301: rheostadt in z-z-Iay filer..ent circ it r.: Kinor rheostadt in x—ray iilanent circuit KA: Killianmeter for electron current of the x- -ray tube S. G. Spar}: gap H.T.: F? figmg '1" '," L. at. O -\ 11' : .J-aO 1r- . IL. 0 _ 8 - High voltage transformer Desk for spectr meter Slit for x-ray beam Crystal (Calcite) Ifirror Ionization Chamber Telesc0pe for Ionization Chamber hilliammeter for triodc filanent Galvonometor TeleSCOpe for Galvanometer Terminals for Electromotive force Terminal for Potentcmetcr Sink for cooling water -12- a) High voltage supply The high voltage supply consists of a Kelly Hoett type J A Special 90 high voltage transformer rated at 114 kilovolts and $25 millianperes, which is supplied by a :30 volt A C source controlled through on auto trans- former rated from 20 to 250 volts A C at 60 amperes. A kilovolt meter, calibrated for this high voltage trans- former, is located in the auto transformer. A transformer along with an on-off switch on the panel board, control the high voltage supply which is taken from the center tap of the high voltage transformer. b) Rectification unit The four fiachlett diodesi‘l are connected in two parallel sets, each set consisting of two tubes in series, thus giving full wave rectification. They are mounted on four elliptically shaped flat aluminum bases Spaced at least 6 inches apart in a wooden box, 1; by 1% by 4% foot with a blower which forces approximately 50 cubic feet of air per minute into one end of tie box and out the other. The filaments are supplied from two sets of air-insulated step-down transformers, each with a single rimar and two secondaries. Each prima v is wound on U *lI'Iachlett VT 14-1 11.5 115 volts so mperes filament, ylate (air 50 cubic ieeLa/minute) 50 ltilovolts. - l f )1 the arms of a hollow square of laminated trm 1sformer iron app.1roximate1y 1.5 feet in outside dimensions and with a 2 by 2 inches cross section. These are mounted vertically on a wooden frame. The seconLaries are dou3h— nut-shaped,1~ feet in diameter with two of them (for 1:1 and K4) supported vertically on 312 ss tubes at right anb les to and interlocking with their respective primaries. The other two secondaries (for K2 and K3), which are at ground potential, are supported oblicuely on a ban :elite rod but allowed to touch their respective primaries. The data on the filament trans formers are as follows: Table 1 Data on filament transformers. Kc. of Hire K0 load Full load winding Size volta3e volta3e KTl: primary I 29 E0. 14 120 V 120 V secondary for K1 47 Do. 14 19.5 V 10.5 V secondary for Kg 35 No. 10 14.5 V 10.5 V KTB: primary 265 Do. 14 120 V 120 V secondary for :3 2 E0. 10 13.5 V 10.5 V secondary for K4 40 No. 14 18.1 V 10.5 V The current drain in each diode is about 19 amperes. Differences in wire sir e, number of windin3 s, a1d no load voltages arise because the primaries and mec01dcries for K1 and K4 were sa 1va.ed from an e: rlier x-ra; unit and secondaries for K2 and K3 were wound to give the same _ 14 _ out-put voltage with the rectifyin3 diodes in the circuit rather than to gixe similar impedance characteristics. If all the filament windin3s had been wound in the same manner, the impedances would have been matched in aeh case. The plates of K1 and K4 are connected to the second- ary of the high voltage transformer. The output is taken from the center tap of that winding. 0) X-ray filament circuit The x-ray filament circuit is connected to the negative side of the hi3h voltage supply. This necessitates the housing of the x—ray filament supply and its control resistances in a wire cage (2.5 by 1.6 by 2 feet) made of 1/4 inch square wire net. This cage is connected to the secondary center tap of the high voltage transformer and is well insulated from ground by porcelain insulators. The x-ray filament transformer (XT) made by I—ray Corpora- tion in Chicago sets on the floor under the cage. The secondary supplies 20 volts A C with no load, 6 volts A C 4 amperes with full load at a primary volta3e of 120 volts. The X-ray tube filament has an impedance of less than 1.5 ohms for a 60 cycle A C source, so two variable resistances (the larger R 5 to 10 ohms, the smaller r o to 1 ohm) are inserted in series with a 6 ohm pilot lamp in parallel with x-ray tube filament. The leads from the hi3h volta3e cage to the x-ray tube filament in the lead box _ 15 _ 30 throu3h a 1 inch conduit, which is connected to the hi3h volta3e case and insulated by porcelain insulators from the lead box which is grounded. The x-ray filament circuit is connected to the ca3e through a milliammeter (HA) which shows the electron current throu3h the x-ray tube. d) Lead box and x—ray tube The x-ray tube is mounted in a lead box (L), 5 by 5 by 4 feet, framed by 1/8 by 3 inches L section angle irons to which 1/8 inch lead plates are screwed. 0n the hi3h voltage transformer side the entire wall of the lead box constitutes a door which Opens to allow aeess to the inside. 0n the other side, at the center of wall of the lead box is a hole 1 by 2 inches with a lead door (1D) which may be closed and Opened by an electroma3net which is activated by the switches (OS and C.S) and a battery (LDB). A water-pressure switch inside the box is connected to the return flow of the coolin3 water pipe. The x—ray tube has flat molybdenum tar3et and is mounted as shown in Fig. 6. e) Safety apparatus The entire x-ray system except the control panel is enclosed in a wire ca3e, 9' x 9.25' x 7' high, made of one inch wire mesh and supported by a wooden frame work _ 16 _ of 2 x 4“s lumber. All conducting parts of this main ca3e are grounded. On one side is a door 3% feet wide. A shorting bar is fastened on the tOp of the door (see Fig. 1) so that as it is Opened this bar makes contact with the hi3h *Olta3e conduit. The bar is made \ 3' of a steel rod 5 feet lon3 and 5/8 inch diameter, and bent as shown in F13. 1 so that its end is 12 inches from the conduit when the door is closed and makes contact to the conduit with the least motion of the door when it is opened. ' The contactor switch of the door (DS) and the water pressure switch (JS):are inserted in series in the circuit of relay (SR). If the door is Opened b; nistahe the con- tactor switch Opens the relay circuit and cuts Off the main electric source for the auto-transformer. The water . ‘ . ressure switch (HS) insures the water coolin3 of the x- ay w C... arget in the same way. f) Spectrometer O The spectrometer system is composed of three lead slits, a calcite crys al (Or), an ionization chamber (I), . , . * a re31stance br1d3e t and a galvanometer (G). All of these are mounted on a ri3id wooden table except the f . £4 an fieeds and Korthrup CO. Ser1al number 544054, Cata103 number 7675. - 17 _ galvanomcter which is set on a wooden beard fastened to the frame of the main cage is shown in F13. 7. The telescope (Ta is used with the galveiometer (G) and the telescOpe (T1) is used with the ionization chamber (1). Once the readin3 of the telescope (Ti) is recorded when the x—ray beam is enterin3 the ionization chamber, the same reading will always insure that the bean is entering the chamber. The preliminary calibration is made with the aid of a fluorescent screen. The reading is taken from the scale mounted On the tOp of the ioniza- tion chamber as reflected by a mirror rigidly mounted on the crystal holder. The electric connections of the electrometer tube circuit, galvanometer, and ionization chamber are shown in Fig. 1. Variable resistance Ho. 1 of the brid3e is 10 kiloohms and No. 2 is 100 ohms. The triode is a RH 508, and the variable filament resistance is 18 ohms and the bias resistance is 55 ohms. Since the filament current of the triode should be very steady, the filament current should be turned on several hours before the experiment be3ins. Further details will be discussed in the next section. III CIERATICI AID TESTIIG CF ArJAEATUS a) Operation we now discuss the Operation of the various con- trols in the system. The method by which various ceitrols function can best be explained by indicating the consecutive steps used to nut the system into Operation. 1. '7')! 5. The flow of cooling water is increased until one hears the pressure 3 itch inside the lead box close. The magnetically Operated shutter coveriig the gort from the lead box housing the x—ray tube is closed by pressin" the switch (CS). The door to the large wire cage is closed. Care must be take n that the door is completely shut in order that the contector switch goanted on the door f1 ame closes. Close the 115 VAC switch (81). This supplies the voltage for the filarents of the rectifier diodes, for the motor of the blower, and for the iiircry of the x-ray f-.19i' ent transformer (KT) Close th x-ray filer |_) ent switch. This switch is in the small wire cage within the larger csge. It is controlled by a sraall bakelite rod (1) runiing out through the side of lcr e cage. Th~ small pilot lamp indicates when t'“.e current is on. The r. current may be adjusted by rods (2 and a). 7. ki) 10. ll. Turn on the 270 VAC f—phase switch (So). If the safety switches are closed one will hear the click he relay sw.itch closes. Turn on the main switch (SE) of LC VAC l—single uha se. Then adj ust this voltage by selecting th preper tap of the auto-tre.sforner. A rough estimate of the out put of the high volta 5e t1 ans_or er can be obtained by the voltmeter on the pslel boa1d. This voltmeter is calibrated to read directly the seeo ry voltage of the high voltage transfer: er. Teri o the transfo ormer miitch (I ‘8), after one ria“es sure that relay switch on the control panel board is ‘rq f‘f-Q ‘9“; g; ctre meter, the filament curren re 0 s U) (D 6+ : a (D ti.) circuit of the triode R3508 should be turned on several hours before the experiment starts. Adjust the filerw current to about 50 milcamperes .ith H: the aid 0 filament variable resistance (l8 ohms) and the niliammeter (MAP). Set the crystal (Cr) to the osition of the largest angle of the range of angles wFich the exper'ncnt requires, with the aid Of tangent‘ screw. Set the ionization chamber to such a po ition th at the reflectc' d X-rays hit the window of the ionization ‘\ chamber, with the aid of telescOpe (Ti), mirror on crystal holder, and the scale on the tOp of the chamber. _ 20 _ 12. Close the galvanoneter circuit and balance the bridge with the aid of variable resistance Ho. 1 (10 kilo ohms) for rough adjustment and Ho. 2 (100 ohms) for fin adjustment. 2. After the galvanometer is settled down, read the scale with the aid of telescOpe (T3). 14. Open the lead door (LB) with the aid of switch (OS). 15. Read the maximum deflection of the galvanometer. 16. Close the lead door (LD). 17. Change the angle of crystal and position of ioniza- tion chamber for next step. 18. After the galvanometer has settled down, read the scale of galvanometer and repeat the above process. b) Testing and testing data The calibrated spark gap meter (Sh) was used to check roughly the reading of the hilovoltmeter (KV) with good agreement resulting in the range from 20 to 55 kilo- volts. The electron current through the x-ray tube is variable in the range from O to lO milliamperes. The testing data of continuous, characteristic, and absorbtion spectra are shown in Table l and 2 and Fig. 8 and 9. The calibration and calculation from these are as follows. The following calibration holds for a molybudenum target with a silver absorber and a calcite crystal in the spectrometer. The wave lengths of the characteristic V a, M n .1 . 9 . . q 9*1 . x-rajs 110m molybudenum are 0.71 a and 0.6c a re- spectively, and the absorbtion limit by silver is *3 . . 1, . 0.48448 91 . The Bragg relation is n7~ = ea Sine , 1 0*. . . where d = 3.05560 A 4 for calcite, x :3 wave length of Pb O H Q 4 (I) d- a (‘3 B p; x—ray beam, 9 is the reflecting angle o n is positive integer. And for small an tan 9 = t/r, vhere t is the tangent screw readina in millimeter and r is the distance from the tangent screw to the center of crystal rotation which is about 119 millimeter. If we let lOOt = (x I x0), then we get following results with the aid of Tables 1 and 2. x(in 3) : (2d/r)t : (Zd/lOOr) (x x x0) 0.71 = o.oooeii(icio ¢ x0) x0 = 80‘ 0.65 : 0.0005ll(ll5O / x0) x0 = 5’ 0.48448 : o.ooosii(evo x x0) x0 - 78‘ We take the averaae x0 = 80. From Fig. 9, the cut-off wave length is A = 0.00CSll(5OO z 80) = 0.29628 3. Therefore the peak voltar‘e is 12.378/O.29638 = 41.76 KV. This agrees ap- proximately with the reading of kilovoltmeter (KV) which was 41.5 KV. * 3Aproull:Xyray in practice 4 o v I ' Compton and Allison: X—ray in theory and experiment. g;- I Z‘ 'I Fig. 10 sh we the wave form of the rectified voltage - it is poor because adequate filtering could not be used. Table 2 Data used in calibration of the instrument,target:£o. tube currentz7 1A,filament:4.2 A,4l.5 K7. 1: Kicremeter reading for calcite crystal angle y: Galvanometer reading for intensity (Ti reads 6.1 on scale) x y X y 1700 2.5 1155 15.5 1650 2.5 1150 16.5 1600 2.7 1145 15.7 1550 2.9 1140 15.1 1500 5.0 1155 14.7 1450 5.2 1150 10.6 1400 5.4 1125 7.1 1575 6.2 1100 5. 1550 19.6 1150 5.2 122 55. , 1100 5. 1520 57.7 950 5. 1515 58.7 900 E. 1510 59.5 850 2.5 1505 58.1 800 2.5 1500 57.5 750 2.1 1275 10.1 700 1.8 1250 4.7 650 1.4 1200 F. 600 0.9 1175 6.5 550 0.5 1170 10.5 1165 14.2 1160 15.0 Table 5 Data on absorption edges of Ag absorber Ag(90%) Pb(lO%) thickens 1/400 inch x y 1000 1.1 950 1.0 925 0.9 900 0.8 895 0.8 890 0.8 885 0.7 880 0.5 875 0.5 870 0.4 865 0.5 860 0." 855 0.2 850 0.2 825 0.2 800 0.2 775 0.2 750 0.25 bx kx ax 1Q sex M\ Ns \\ 3 s ”‘— ___-(./ firfi N d. ON «a .Nm .3 0.. .3 ma \‘1 \O 533. to IV CONCLUSION With this unit, some analytical study of con- tinuous x-rays, ieasurement of absorption edges, and taking Laue and powder pictures can be done quite sat- isfactorily. One weak point of this apparatus is that the insulation of the rectifiers begins to break down in the neighborhood of 50 kilovolts, particularly along the outer surface of the glass envelOpe from anode base to filament leads, and especially when it is run for long periods. V REFERELCES Compton and Allison: X-ra‘ in Theory and Experiment (2nd ed.). Sproull: X-ray in Tractice (lst ed.). Clark: Applied X-ray (3rd ed.). Terril and Urey: X-ray Technology (1950). G. E. Harnwell and Livinggood: Exocrimental Atomic Physics. Ridchnyer and Kennard: Introduction to Kodern Enysics. fiilliam Richard Struwin: Design and Construction of a Kilovolt-Ieter for Use with X-ray Lacnines. Newman Pettit: The determination of x-ra” mass absorbtion d coefficients for Columbium from .800 to .100 3 units. HICHIGRN STQTE UNIV. LIBRRRIES I III "I 1 312930 7709084