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"-‘- ’ _ a“ .. o ‘- "-1 oor‘t.(-, . -»‘ '-.~-’onl.v to ~ --4 . 4“... .‘vd’t ' pa. 0' ‘Uv’o‘f' “0"!” 'fo'—‘ ; V' I. a 'I' ..oorov c-lr\ ' o o. - '. 4-~. . (no. Kk‘aaé’v Eun;/::'-:;-um IllfllflmfflmflWWIHIIWHUWI L 1293 00709 1196 LIBPARY FEVIZLS .1112 311 Si, rate Lira U21 vets: ty $5.», in“ ._ ABSTRACT IDENTIFICATION OF TRACE ELEMENTS IN HUMAN BLOOD BY NEUTRON ACTIVATION ANALYSIS by William W. Freeman A procedure is presented for the identification of the trace elements in human blood using neutron activation analysis, a radio- chemical separation and gamma-ray spectrometry. It is proposed that, using this procedure, the unique character of an individual blood sample may be determined and that its origin may be identified. Data is presented on the trace element content of blood samples from several donors and comparisons of the samples are made. IDENTIFICATION OF TRACE ELEMENTS IN HUMAN BLOOD BY NEUTRON ACTIVATION ANALYSIS By .. .?~ William WI'Freeman A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Criminal Justice 1971 Approved: YL.‘ I.I’——}: £04;::::3 Mr., alph F. Turner, Chairman ' a, La. (MA... (‘4 Dr. ce W. Wil inson 0“ @‘f‘ Mr. Clarence H. A. Romig m \J ACKNOWLEDGEMENTS I wish to express my sincere appreciation to the following members of the Michigan State University faculty under whose guidance this study was completed: Professor Ralph F. Turner, my Major Professor and Committee Chairman, fbr his advice throughout the course of the study and for his help in the drafting of this thesis. Dr. Bruce W. Wilkinson, my Research Advisor, without whose advice and assistance, in dealing with the many technical problems which I encountered, this work could not have been completed. Mr. Clarence H. A. Romig, for his helpful suggestions and for introducing me to the criminalistics field. I wish to express special appreciation to my wife Regina, whose patience, understanding and assistance has enabled me to complete this thesis and my education. ii TABLE OF CONTENTS PAGE List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . v List of Figures . . . . . . . . . . . . . . . . . . . . . . . . vi CHAPTER I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . l The Problem . . . . . . . . . . . . . . . . . . . . . l Hypothesis . . . . . . . . . . . . . . . . . . . . . . 3 II. HISTORY OF NEUTRON ACTIVATION ANALYSIS . . . . . . . . . 4 III. HISTORY OF NEUTRON ACTIVATION ANALYSIS IN THE CRIMINALISTICS FIELD . . . . . . . . . . . . . . . . . 5 IV. EXAMPLES OF CURRENT INDUSTRIAL AND ACADEMIC USES OF NEUTRON ACTIVATION ANALYSIS . . . . . . . . . . . . 7 V. PRINCIPLES OF NEUTRON ACTIVATION ANALYSIS . . . . . . . 8 Neutron Interactions . . . . . . . . . . . . . . . . . 8 Detection of Radioactive Emissions . . . . . . . . . . 12 Interactions of Gamma Rays with Matter . . . . . . . . 13 Scintillation Counting . . . . . . . . . . . . . . . . 14 The Multichannel Analyzer . . . . . . . . . . . . . . 15 Germanium-Lithium Detectors . . . . . . . . . . . . . 17 Analysis of Data . . . . . . . . . . . . . . . . . . . 19 VI. COMPARISON OF NEUTRON ACTIVATION ANALYSIS WITH OTHER ANALYTICAL TECHNIQUES . . . . . . . . . . . . . 21 iii CHAPTER PAGE VII. NEUTRON ACTIVATION OF BLOOD . . . . . . . . . . . . . . . 26 The Nature of Blood . . . . . . . . . . . . . . . . . . 26 The Problems in Analysis . . . . . . . . . . . . . . . 28 A Review of the Literature . . . . . . . . . . . . . . 29 VIII. EXPERIMENTAL PROCEDURE . . . . . . . . . . . . . . . . . 32 Instrumentation . . . . . . . . . . . . . . . . . . . . 32 Reagents . . . . . . . . . . . . . . . . . . . . . . . 32 Blood Samples . . . . . . . . . . . . . . . . . . . . . 33 Procedure . . . . . . . . . . . . . . . . . . . . . . 33 Gamma Ray Spectra . . . . . . . . . . . . . . . . . . . 40 IX. RESULTS AND DATA . . . . . . . . . . . . . . . . . . . . 44 X. DISCUSSION OF RESULTS . . . . . . . . . . . . . . . . . . 51 Sources of Error . . . . . . . . . . . . . . . . . . . 53 XI. CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . . . . 54 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . 57 APPENDICES A. Current Forensic Applications of Neutron Activation maIYSiS O O O O O O O O O O O O O O O O O O O O O 0 O 61 B. Quantitative Analysis . . . . . . . . . . . . . . . . . . 62 C. The Use of Neutron Activation Analytical Evidence in Court . . . . . . . . . . . . . . . . . . . . . . . 63 iv TABLE LIST OF TABLES History of Neutron Activation Analysis . History of Neutron Activation Analysis in the Criminalistics Field . Common Reactions for Production of Radioisotopes . Comparison of Detection Limits of Neutron Activation Analysis and Other Analytical Techniques . Micrograms of Lead Per Milliliter of "Moonshine" . Elemental Content of Whole Human Blood . Elements Detected in Human Blood . Differences in Number of Elements Found Between Pairs of Samples . Elements Found in Individual Blood Samples . PAGE 12 22 24 27 45 46 48 FIGURE LIST OF FIGURES Nuclear Process Chart . Gamma Spectrum of 24Na Schematic of Detection System and Multichannel Analyzer . . . . . . . . . . Ion Exchange Column . Gamma Ray Spectrum of Whole Human Blood Before Radiochemical Separation Photopeaks Visible After 24Na Removal . vi PAGE 16 18 37 42 43 CHAPTER I INTRODUCTION The Problem One of the most frequent, and often one of the most important, pieces of evidence found in the process of investigating a crime is blood. In most crimes of violence such as murder and assault, blood may be found at the crime scene in general, but particularly on the victim's person, on the weapon, and occasionally on body or clothing of the perpetrator of the crime. The individualization of blood is therefore a valuable technique in providing evidence which may associate a suspect with, or eliminate him from, the crime scene. Nearly all of the chemical and spectroscopic tests for blood that are presently used (such as the Benzidine, Luminol, and Teichmann (crystal) tests) are based on the detection of hemoglobin or its deriv- atives. Chemical examination of suspected blood stains can determine whether or not the material actually is blood, whether it is human or animal in origin, the blood group to which the person belongs if it is human in origin, and the presence or absence of syphilis in the donor (using whole blood). The four major blood groups into which blood is presently classi- .fied, based on the presence or absence of the A and B agglutinogens, give only a general classification of the individuals in the human race. Kirk1 lists the occurrence in the population of the various blood groups, and this shows that almost half of the human race (43%) have type "0" blood, and while only three percent of the people have type "AB" blood, this still yields only a broad distinction. Further distinctions, beyond that of the four major groups, can be made based on the presence or absence of type M and N agglutinogens and by identifying the eight Rh blood types. Under optimum conditions of freshness, quantity, and preservation, by using the various groups and subgroups (types), two hundred and eighty eight kinds of human blood can be identified.2 In the great majority of blood examinations done in the forensic laboratory, the identification cannot go beyond the determination that the blood belongs to one of the four major groups. Some useful conclusions can be drawn, concerning the source of blood specimens, using these rather broad groupings and types, such as showing that the blood could ngt_have come from a certain individual. This information is valuable, for example, in eliminating persons as suspects in a crime or in settling paternity problems. There is no technique presently available, however, whereby blood can be identified as coming from a particular individual. There is no 1Paul L. Kirk, Crime Investigation, Interscience Publishers, New 'York, 1960, Chapter 13. 2C. E. O'Hara, Fundamentals of Criminal Investigation, 2nd ed., Charles Thomas Co., Springfield, 111., 1970, p. 453. procedure which would allow the forensic chemist to determine, for example, not only that the suspect in a criminal investigation is one of the 14% of the population that has type "B" blood, but also that the suspect's blood has individual characteristics which set him apart from all others in that 14% grouping. The late Dr. P. L. Kirk, Professor of Criminalistics at the University of California (Berkeley), discussed in his paper "Some Criminalistics Problems, and Neutron Activation Analysis", the importance of trace elements in establishing, with increased probability, the possible common origin of two evidence samples--whether natural or manufactured materials. He said, "With the great sensitivity of high-flux N.A.A., many trace elements can be quantitatively determined in most materials, even when only tiny specimens are available. This can greatly extend the capabilities of the criminalist in his comparisons of evidence samples.3 N.A.A. has already been used in the identification of indi- viduals by determining the trace element content of hair samples.4 Based on this discussion, the fOllowing hypothesis is advanced. Hypothesis By means of an extremely accurate analytical technique such as Neutron Activation Analysis (which may be used to examine extremely minute pieces of evidence), it should be possible to individualize blood samples. This identifi- cation of blood as coming from a unique source, rather than a broad group, could be made by characterization of the various trace elements which are present in human blood. 3V. P. Guinn and R. H. Pinker, The WOrld-Wide Status of Forensic Activation Analysis, paper presented at the 19th Annual Meeting of the American Academy of Forensic Sciences, Honolulu, Hawaii, February, 1967. 4R. E. Jervis and A. K. Perkons, "Applications of Radio-Activation Analysis in Forensic Investigations", Journal of Forensic Sciences, I, 4, 449, (1962). CHAPTER II THE HISTORY OF NEUTRON ACTIVATION ANALYSIS Soon after the discovery of artificial radioactivity in 1934, scientists began to use this new technique of nuclear transmutation as a test for minute traces of elements in various materials. Table 1 shows a chronological list of various developments in the field of neutron activation analysis (N.A.A.), as it went from a mere laboratory curiosity, three decades ago, to a widely used analytical tool, today. 1938 1943 1947-1948 1952 1953-1971 1969-1971 TABLE 1 Seaborg and Livingood1 detected extremely small amounts (6p.p.m.) of gallium in iron samples. Oak Ridge National Laboratory began to use N.A.A. as an "everyday procedure" for the detection of impurities in metals and alloys. Equipment became commercially procurable for the detection and measurement of all types of radiation given off by radioactive decay. The Oak Ridge National Laboratory made an Activation Analysis service available to the public. Many more research-type reactors were built, both at Atomic Energy Commission (AEC) facilities and at non-AEC labs. More sophisticated and efficient radiation detection equip— ment became available. 252Californium neutron sources were made available, allowing N.A.A. to become portable, or not dependent on a nuclear reactor site as a source of neutrons. 1G. Seaborg and J. Livingood, "Artificial Radioactivity as a Test for Nfixnate Traces of Elements," Journal of the American Chemical Society, 60, 1784 (1938). CHAPTER III THE HISTORY OF NEUTRON ACTIVATION ANALYSIS IN THE CRIMINALISTICS FIELD Within the last ten years, N.A.A., which had already gained accep- tance as a precise analytical technique in various industrial and academic applications, has begun to be used as a tool of the forensic scientist. Table 2 shows a list of the recent developments in the for- ensic science field. TABLE 2 1959 At the suggestion of the U. S. Atomic Energy Commission, studies were begun, at the Oak Ridge National Laboratory, to test the applicability of N.A.A. in the forensic science field. 1962 Strong evidence was discovered,1 that Napoleon Bonaparte died of arsenic poisoning (either intentional or accidental). This was determined by N.A.A. of samples of his hair. 1963 N.A.A. was used to detect Barium and Antimony (gunshot residues) on both hands and the right cheek of Lee Harvey Oswald, in the investigatiqn of the assassination of President John F. Kennedy. 1964 The first test case in the U. S. in which the pgosecution's case rested almost entirely on N.A.A. occurred. This involved the analysis of paint particles on a tire iron. 1Smith, Forshufvud and Wassen, "Distribution of Arsenic in Napoleon's Hair," Nature, 194, 725 (1962). 2J. Lenihan and S. Thomson, Activation Analysis, Academic Press, London, 1965, Chapter 19. 3Time, Aug. 7, 1964, p. 58., "Atomic Fingerprints" TABLE 2 (Cont'd) 1968 a) N.A.A. was first used in a civil suit4 involving Mercury poisoning of race horses. b) N.A.A. resulgs were first presented by the defense in a criminal case; (all previous uses of N.A.A. were by the prosecution). 1970 The Stifel case was decided.6 Up to the present time, it has set the legal precedent regarding the admissability of N.A.A. results. N.A.A. was used to identify fragments of a package which contained a bomb. x Vv—v— j 4V. Guinn and M. Pro, Transactions of the American Nuclear Society, 12, 506, (1970). T ‘7 5Ibid. 6U. S. v. Stifel, No. 19958, U. S. Court of Appeals (6th.Circuit), Oct. 29, 1970. CHAPTER IV EXAMPLES OF CURRENT INDUSTRIAL AND ACADEMIC USES OF N.A.A. In recent years, N.A.A. has become an increasingly more useful analytical tool and has found a variety of applications in diverse industrial and academic areas. For example, N.A.A. has been used to detect the amounts of arsenic, copper and mercury in different layers of tooth enamel in a study of means to prevent dental caries. N.A.A. is now being used extensively in the areas of Cosmochemistry and Geo- chemistry, for example, in the analysis of meteorites1 for the heavier elements such as indium. In the plastics industry, N.A.A. is used to detect the amounts of the polymerization catalysts2 (in many cases, Ziegler's catalyst, containing Titanium and Aluminum) which are carried over into the final product. Today, N.A.A. is being used in the field of enviornmental studies, for example, to detect trace amounts of poisonous metals such as mercury and arsenic in water supplies as well as in fish and wild life. This writer has recently used N.A.A. to determine quantitatively the amount of mercury in various species of fish taken from waters in the Great Lakes area . 1E. M. Burbidge, et_al., "Synthesis of the Elements in Stars," Rev. Mod. Phys., _2__g, 547, (195757 "" 2Lenihan and Thomson, Chapter 20, p. 130. 7 CHAPTER V PRINCIPLES OF NEUTRON ACTIVATION ANALYSIS Neutron Interactions Neutron Activation Analysis (N.A.A.) is essentially a method of making qualitative and quantitative elementary analysis by means of nuclear transmutations. Upon exposure to the nuclear particles produced by a nuclear reactor, particle accelerator, or other source, some of the atoms of the target material are converted, by interaction with the bombarding particles, into different isotopes of the same element or into isotopes of different elements, depending on the natures of the bombarding particles and bombarded material. The bombarding particles can be neutrons, protons, deuterons or even high energy gamma photons. The target atoms, which, as a result of this bombardment, undergo transmutations and become radioactive, have discreet radiation properties which can serve both to identify and measure the quantity of an element in a sample. This radiation may be emitted either during the instant of bombardment or in the course of radioactive decay. The nuclear process chart1 (Figure 1) can be used to predict which isotope will result from a given nuclear transmutation. For example, a 1R. Wainerdi and N. Du Beau, "Nuclear Activation Analysis," Science, 139, 1027, (1963). target nucleus of mass M (square 6) will be converted to the next heavier isotope of the same element (square 7) upon capture of a neutron. Also, a nuclear process which causes an alpha particle to be given off by the target nucleus will cause that nucleus to have an isotopic mass of GM—4) and all of the nuclear properties of the isotope in square 1. FIGURE 1 Nuclear Process Chart Neutrons are the moSt widely used bombarding particles in activation analysis work, since, for charged particles, there is always a threshold energy which must be overcome before activation takes place, and, with the exception of some of the light elements, most elements have low capture cross-sections for the charged particles. In the case of the high energy photons, the threshold energies are even higher and the capture cross-sections are even lower. The attention here, therefore, will be devoted to neutron bombardment and the resultant reactions. 10 Since neutrons are neutral particles, they are not inhibited by a threshold energy which.must be overcome before nuclear interaction can take place. Also, most nuclei have reasonably high capture cross sec- tions for thermal (slow) neutrons. The production of radioactive nuclides is given by dN' 7E— : ONT (1) l where N' = Number of product nuclei due to neutron absorption N = Number of parent atoms of a particular atomic and mass number in the sample 0 = Cross-section for the production of radioisotope N' in units of cm2. o = Neutron flux in units of neutrons per cm2 per second (n/cmZ-sec). t1 = Irradiation time If the product is radioactive with a half life, T the disinte- 1/2’ gration rate at any time is dN' - AN' -0.693 N' dt = = 'T (2) 1/2 Upon combination and solution, equations (1) and (2) give -1t N' = 0N¢ (l-e 1) (3) The amount of activity, At’ in units of disintegrations per second, exhibited by the atoms N' produced up to a time t1 is given by the expression At = AN' = oN(1-e-At1) = Am(l-e “3'69“ 3 (4) 1/2 11 where the product @oN in equation (4) is the saturation activity, Am, or theoretically, the saturation produced by an infinitely long irra- diation. The factor within the parenthesis in equation (4) is termed the "saturation factor," S, which varies between zero and one. The rate of decay of the product radioisotope will be proportional to the number of radioactive atoms present. At the beginning of an irradiation, there are no (or extremely few) radioactive atoms present and the rate of decay is insignificant compared to the rate of production and the amount of activity will increase linearly with.exposure time. While the population of radioactive atoms is increasing, some are already beginning to decay, and as the decay rate becomes greater, the net pro- duction rate begins to decrease. A point is finally reached at which the rates of production and decay are equal, and no greater radio- activity will be produced upon further irradiation. This is the satura- tion point or limit. The common reactions for the production of radioisotopes by neutron activation are listed in Table 3,2 where A=mass number, Z=atomic number, n=neutron, p=proton, a=alpha particle, and y=gamma ray. 20. J. Hahn, Application of Neutron Activation Analysis in Criminal Investigations, Bulletin 89, College of Engineering1PUhive§§ityjof Kentucky, Lexington, Kentucky, 1969. 12 TABLE 3 COMMON REACTIONS FOR PRODUCTION OF RADIOISOTOPES Reaction Notation Predominate Energy_of Neutrons AZ+n+A+1Z+y AZ(n,y)A+1Z Thermal (0.025 electron volts at 20°C) * * AZ+n+A Z+n AZ(n,n')A Z Fast 1-3 MeV * AZ+n+A(Z-1)+p AZ(n,p)A(Z-l) Fast 1-3 MeV * AZ+n+A-3(Z-2)+a AZ(n,a)A‘3(Z-2) Fast 10-20 MeV * AZ+n+-A.12+2n AZ(,n,2n)A'12 Fast 10-20 MeV * *Approximate threshold energies in Million electron volts below which.the reactions are not possible. The first reaction is most predominant with thermal neutrons. A nucleus with mass number A and atomic number Z is transformed to a radioisotope with mass number A+l; the excess energy is given off as a gamma ray. The remaining reactions in the table, such as inelastic scattering (second equation) and the neutron-proton reaction (third equation) generally take place only with high energy neutrons. Detection of Radioactive Emissions Various instruments such as Geiger-Mueller counters, scintillation counters, and semiconductor detectors, are commercially available for the detection of charged particles and/or gamma rays. In activation analysis using thermal (slow) neutrons, 8‘ particles, and particularly y-rays are the types of radioactive emissions usually investigated. 13 Beta particles (8-) are not monoenergetic but exhibit a continuous energy distribution from zero to a maximum value which is character- istic of the emitting nuclide.3 Most samples will, upon irradiation, contain more than one B- emitter, each with its own continuous spectrum, and a chemical separation of the nuclides must be made before measure- ments can be undertaken. Almost all activated nuclides emit characteristic monoenergetic y-rays. The qualitative and quantitative identification of the various elements present in the material being analyzed can be determined from the total y-ray spectrum. Interactions of Gamma Rays With Matter When a y-ray quantum is incident on a material, its energy can be transferred in any or all of three ways.4 Photoelectric absorption involves the ejection of one of the orbital electrons from the atom. The outer electrons are more easily removed than those closer to the nucleus. The y-ray actually imparts all of its energy to the orbital electron, which, upon ejection, has a kinetic energy equal to that of the original y—ray minus the binding energy of the electron. This is the major mode of interaction for low energy y-rays. Compton scattering, or the Compton effect, is the transfer of only part of the energy of a y-ray to an electron. The y-photon is deflected 3W. 8. Lyon, Guide to Activation Analysis, Van Nostrand Co., Inc., New York, 1964, Chapter 6. 4Lenihan 8 Thomson, Chapter 3. 14 or scattered as though an elastic collision has taken place. The photon moves at an angle, dependent on the particular collision involved, with an energy less than that of the original y-ray. The Compton electron is also scattered at an angle, with a given energy value. The third possible interaction is pair production. In this case the y-ray vanishes completely and its energy appears in the form of B+-and B--particles. The threshold fer this phenomenon is at 1.02 MeV, since the rest mass energy of each particle is 0.51 MeV.5 The probability for pair production increases with energy. The reverse effect, electron- positron annihilation, is also possible. In this case, the two particles collide and their energy and mass are converted into electromagnetic radiation. Instead of one quantum.being formed, two quanta, each moving in opposite directions, are formed, and each has an energy of 0.51 MeV. Scintillation Counting_ Phosphors are solid or liquid materials which have a high fluor- escent efficiency and high absorption for y-radiation. When the reac- tions described above occur in a phosphor material (such as the inorganic solid phosphor, NaICTl), sodium iodide doped with Thallium), the processes of de-excitation and recombination convert the absorbed energy into light pulses or "scintillations."6 The phosphor has a photocathode, or photomultiplier tube on one side of it so that electrons will be emitted when light pulses strike its face. These electrons are multiplied by 5Lenihan 6 Thomson, Chapter 3. 6J. Bowen and D. Gibbons, Radioactive Analysis, Oxford University Press, New York, 1963. ' V 15 secondary emission from a series of amplifying tubes or transistors, eventually resulting in a millivolt signal which is sent to the counting and discriminating equipment. The Multichannel Analyzer The analysis and distribution of these signals (pulses) are carried out by a multichannel analyzer which may have, for example, from 512 to 4096 channels. In the modern, so-called computer type multi- channel analyzer,7 there is first an analog to digital conversion in which a number is generated in response to each pulse. This number, known as the channel address, then goes into a computer and is stored as a count in the appropriate section of the memory of the analyzer. After the radioactive sample has been "counted" in this manner for the desired (pre-set) time, with the counts per channel being stored in the memory, the resultant y-ray spectrum can be displayed. This display can be in the form of a trace on an oscilloscope screen and/or a print- out on a chart recorder. The information can also be printed out digitally or punched onto paper tapes. Figure 28 shows the gamma spectrum of 24Na, as it would appear on an oscilloscope screen or recorder chart. Since the modern analyzer systems use memory-cycle storage times that are relatively long (10 to 20 u sec.),9 a device called a "live 7Lenihan and Thomson, Chapter 5. 8Lenihan and Thomson, Chapter 3 9Lyon, Chapter 6. 16 .>ox ow xmaocm eaamu emnm memm mmna mama Ham - pl r p I q I d 1 fleseeeme .\ $388 \ mxeom . omeomm omwm _ :oumfiou nowpefivem eeeeeaeeeee< GOAHQHOmn< aflnpooHoouond dz em _\ Hoppeomxoem mo znmhummm <22zou a O 0 $53.23 00.324 @ 001.424 8. .565 ..>.. ..x.. op .566 - _ O . O . O mammncbz {—1 $22451...“qu «F «0.5352. 550.5 mmmmooq . esqmmnq \ $39.0er mwpmm>2oo aomrzoo 23m .\ 1| 4365 mmijnzq 1.1 We... flmhznooz or 004424. «492.. h x. v n a . $5.5 Jx _ - . legume \\ .3sz .4...va mo \ Cam . euqmemam . Elfin what 33...? n F .. n 556% . . «05.052. _ mmtmzmni - mmoo «Ho 1L 9...: :9: r mtmmud oqmz ooq n>3 EMN>Jm zoiowbmo *0 0:12m10m 19 production of electron—hole pairs. An applied electrical bias across the detector causes these free charge carriers to move to the outer regions of the detectors, producing an electrical signal which is then amplified and measured. An example of the great resolving power of the Ge(Li) detector is that, using it one can distinguish between the 1099 KeV y-ray of 59Fe and the 1115 KeV y-ray of 652n. This would not be possible with a NaI(Tl) detector. Analysis of Data The data obtained from the output of the multichannel analyzer (e.g. the plot of photopeaks on recorder paper) can be used in both qualitative and quantitative identification of the isotopes present. The qualitative analysis of the elements present in the material being analyzed is obtained by identifying the various photopeaks in the spectrum. This is accomplished by first drawing a calibration line (curve), which is obtained by counting several "standard" materials 6OCo and 137 Gusually long half-life isotopes such as Cs). These "standard" isotopes give off y-rays with precisely known energies, and the "unknown" isotopes in the matrix being analyzed are compared with these. In many cases, this rather straightfbrward procedure is complicated by factors such as the presence (If a large amount of an interfering element in the matrix, causing high backgrounds and poor counting efficiencies fer detection of the y-rays from the trace elements present. A radio- chemical separation after irradiation and prior to counting is often 20 needed to remove these interferences. An example of this is the large amount of sodium present in biological materials. The large amount of 24Na present, from 23Na(1n,y) 24Na, T1/2=lS hours, often precludes the identification of most, if not all, of the trace elements present. The quantitative measurements of the trace elements present in a given matrix may be made by comparing the area under a given photopeak with that of a known standard. A known amount of standard is irradiated and counted under conditions identical to those under which the unknown was irradiated and counted. That is, both are irradiated at the same time under the same neutron flux, etc., then both are counted for set periods of time with corrections being made for radioactive decay (depending on the half—life of the materials), as well as fer background radiation. The counting geometry, that is, the type of container, distance from the detector, etc., should also be kept constant for both standard and unknown. CHAPTER VI COMPARISON OF NEUTRON ACTIVATION ANALYSIS WITH OTHER ANALYTICAL TECHNIQUES An evaluation of N.A.A. as a method for the qualitative and quantitative determination of trace elements is desirable to show its advantages as well as its limitations as compared with other methods of trace element identification. Although the limits of sensitivity for the various other instrumental techniques can be fbund throughout the literature, the values of these limits vary somewhat with different investigators, their experimental procedure, the equipment used, etc. A rough comparison is presented here to show the value of N.A.A. rela- tive to other trace element identification techniques. Table 4 shows the detection limits of N.A.A. and four other methods fer 25 of the most common elements for which the five techniques campared can be used. The other four techniques included in the table are typical methods in general use. The values in the table actually give only an order of magnitude, since a certain normalizing factor must be used to adjust the values to a common sensitivity basis of micrograms. Some values are presented in the literature as micrograms per milliliter, some as micrograms per electrode, etc., as indicated in the table. 21 22 moooo.o moo.o moo.o Hoo.o mooo.o a: m.o meeo.e Noo.o e.o --- m2 Hoo.o o.~ no.0 uu: nu- ma mo.o moono us: nus ooH x Ho.o m.o m.o w.o --- m: moo.o H.o moo.o uuu nu: nu om moo.o Ho.o mo.o o.m on Hoo.o moo.o Hoo.o mo.o o.oH so m.o mo.o nu- nu- 1.. mo o.H moo.o Ho.o N.o o.H no Ho.o -u- nu- ¢.o o.oH Ho ~.o -u- m.o o.mN com cu mo.o moo.o H.o H.o o.m we o.H moo.o H.o In- ooH no moo.o nu- -u- nu: com um mo.o mo.o v.o us: o.m~ em Hoo.o om.o o.H ~.o v.o m< Hooo.o moo.o ~oo.o H.o o.H m< nouosouonmoauuomm .<.<.z :oflumHOmn< amenmonpoomm cowpomox :ofiumnpflh v Ouaaou< neofimmHEm peonfio mo>fiuflmcemunoaou mafiauoaonome< undamam neeeemonefizv meHqu oneumema mmaonmume sqflufimnom comm eocoHQMHOpnfi one mosam> :.mofiufi>fiuflm:om mwmxHen< coaue>fiuoam one amnocm Mano p .Ha\wn CM ao>ww mooam> .00 .m .womH ..> .z .maonmfiansd ooeoflomnoucH .zmoomoawoemm moflunnomo< oesop< .=H>eHw .zo Hm0fimoH0Hm :fl mucoaon means new mvoguoz afinmmnmonuoomm :oammem pooafio: ..Hm we .emflmOHvom .< .eeoeeeeHe\mn a“ ne=He> mfiwomfiv .emm «mm .xeeneaeeu Heeeuxflmmaln:nfieeeepez n .He\me eh ee>em ne=Hn> .fimmeev .AAH .ama .eeeeeem :.mvonuoz Honuo new: mflmxflee< soapm>wpo< mo acmwnwnaou "xpfi>fipwm:ow pacemam canny: .oxeflez .zm H.o moo.o moo.o oHo.o o.oH em m.o oo.o Ho.o us- o.N cm Ho.o N.o mo.o Tn- nu- om moo.o m.o no.0 mo.o o.oH pm o.oH m.o No.0 m.o o.m pd mo.o moo.o woo.o eo.o m.o flz moo.o moo.o H.o nu- II. .62 :11 nopoaoponmoauoemm .<.<.z soapmhomn< :mmnmoupoomm :owuoeom :ofipwnwfie w ooafi0u< neowmmfiam poohfla mo>flpflmcemuaoHoo mafihueaouoma< peoEon meeaeeeeeuv e mgmozmm eZen mmpm< mamHmH> mu no: eeueemusm eeuueuua zaeufleemea oooqm 2(233 2H omhumhma mBZmqum n mam<9 46 TABLE 8 DIFFERENCES IN NUMBER OF ELEMENTS FOUND BETWEEN PAIRS OF SAMPLES Samples Number of elements Different Between Samples 1 and 2 4 l and 3 4 l and 4 4 l and 5 3 2 and 3 2 2 and 4 2 2 and 5 3 3 and 4 2 3 and 5 3 4 and 5 l 47 0f the five individual blood samples analyzed, number one was actually put through the entire experimental procedure seventeen times, number two was analyzed four times, and numbers three, fOur and five were analyzed three times each. Table 9 lists the elements seen (as the radioactive isotope) in each of the five individual blood samples and the number of times that the element was seen in separate analyses, along with the gamma-ray energy and half-life of each isotope. Only the last five analyses run on sample one are included in the table because the first dozen runs were made while the optimum conditions of such variables as irradiation time, height of the isotopic exchange (salt) column and retention time on the column were being determined. Because of these varying conditions and the different degrees of radioactive sodium removal, all of the elements were not seen identically until the first twelve "trial" runs were completed. For example, bromine and antimony which have photopeaks sufficiently removed from the peaks caused by sodium contamination were seen in all seventeen of the samples, even though in some cases sodium removal was very poor. .Arsenic and tin, however, were only identified five and six times respectively, after the sodium decontamination procedure was optimized. The last five analyses of sample number one and all of the analyses of the other four samples were run under the optimized and standardized conditions and show very good reproducibility. 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