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Study of Electron Emissions of Some Mass Separated Fission Product Activities James Paul Adams Iowa State University

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Study of Electron Emissions of Some Mass Separated Fission Product Activities James Paul Adams Iowa State University Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1972 Study of electron emissions of some mass separated fission product activities James Paul Adams Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Nuclear Commons Recommended Citation Adams, James Paul, "Study of electron emissions of some mass separated fission product activities " (1972). Retrospective Theses and Dissertations. 5880. https://lib.dr.iastate.edu/rtd/5880 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This dissertation was produced from a microfilm copy of the original document. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the original submitted. The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction. 1. The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity. 2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the page in the adjacent frame. 3. When a map, drawing or chart, etc., was part of the material being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at the upper left hand corner of a large sheet and to continue photoing from left to right in equal sections with a small overlap. If necessary, sectioning is continued again — beginning below the first row and continuing on until complete. 4. The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pages you wish reproduced. I0 —.«a !il* 1••• ^ wiiivoiai&y IVIIWIUIIIIII9 300 North Zeeb Road Ann Arbor, Michigan 48106 A Xerox Education Company 73-3853 ADAMS, James Paul, 1943- STUDY OF ELECTRON EMISSIONS OF SOME MASS SEPARATED FISSION PRODUCT ACTIVITIES. Iowa State University, Ph.D., 1972 Physics, nuclear University Microfilms, A XEROX Company, Ann Arbor, Michigan Study of electron emissions of some mass separated fission product activities by James Paul Adams A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Physics Major: Nuclear Physics Approved: Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. For the Major Department Signature was redacted for privacy. For the Graduate College iowa State univeisîly Ames, Iowa 1972 PLEASE NOTE: Some pages may have indistinct print. Filmed as received. University Microfilms, A Xerox Education Company 11 TABLE OF CONTENTS Page 1. INTRODUCTION 1 11. EXPERIMENTAL FACILITY 9 A. The TRISTAN On-Line Isotope Separator System 9 B. Detectors and Electronics 12 III. EXPERIMENTAL RESULTS 28 A. Beta Decay Energies 28 B. Results formlCC Measurements for the Decay of Xe 4$ IV. DISCUSSION 61 A. Beta Decay Energies 61 B. ICC Determinations for Transitions in the Decay of Xe 68 C. Summary 75 V. LITERATURE CITED 78 VI. ACKNOWLEDGMENTS 82 VII. APPENDICES 83 A. The TWo-Absorber Method for Correction of Scintillation Spectra for Gamma-Ray Contributions 83 B. The One-Absorber Method for Correction of Scintillation Spectra for Gamma-Ray Contributions 86 C. Computer Programs Used for Data Analysis 87 1 I. INTRODUCTION As a result of nuclear fission, neutron-rich nuclei are formed. Most of these nuclei are radioactive, that is, they are unstable toward emission of an electron and anti-neutrino and thus beta decay with half- lives ranging from milliseconds to years. The maximum energy of the beta spectrum is equal to the difference in the masses of the decaying or "parent" nucleus and the subsequent or "daughter" nucleus. Since the mass of a nucleus is the sum of the rest masses of the individual nucléons minus the binding energy holding the nucleus together, knowledge of the mass of a nucleus gives information about the effects of the nuclear forces acting between nucléons. For example, the mass differences be­ tween adjacent isotopes (isotones) reflect the binding energies of the last neutron (proton) in nuclei (1). Knowledge of the ground state feeding and beta decay end-point energy is necessary for an unambiguous determination of the comparative half-life, or log ft value of a par­ ticular beta group, which can be used to predict a range for the spin- parity difference between the energy levels connected by the beta group. In this work, the beta decay end-point energies of seven decaying nuclei were measured, using beta-gamma coincidence and beta singles techniques: the nuclei studied were ^''^Xe, ^''^Cs, '^'xe, '^^Cs, lii2 142 Xe, and Cs. As an unstable nucleus beta decays, the resulting or "daughter" nucleus is often formed in an excited state, and will de-excite emitting a photon. The end-point energy of the beta group feeding an energy level in the "daughter" nucleus is equal to the beta decay energy of the "parent" nucleus minus the excitation energy of the "daughter" 2 nucleus. Since the gamma ray de-exciting the "daughter" nucleus is in time coincidence with the beta particle emitted from the "parent" nucleus, the beta decay energy of the "parent" nucleus can be determined by measuring the end-point energy of the beta group in coincidence with the de-exciting gamma ray. Of the nuclei studied in this work, the 1971 compilation by Wapstra and Gove (2), includes five nuclei, ^^'xe, lAl 142 142 Cs, Xe, and Cs, which had been only predicted previously. 140 140 A1 vager e^ aj|_. estimated the beta end-point energies for Cs, Xe, 142 and Cs to be 6.2 +0.6 MeV, 4.7 ^ 0.5 MeV, and 7.6 +0.8 MeV, respec­ tively (3). However, Wapstra and Gove did not incorporate these estimates into their compilation. Zherebin e_^ aj_. measured the beta decay energy 140 for Cs to be 5.7 0.1 MeV (4). In 1948, Levy and Zemal reported the beta decay energy for the decay of l8-min '^^Ba to be 2.9 MeV (5). Maly ej^ aj_., in 1958, measured the energy of the same decay to be 1.93 MeV (6). The most recently reported measurement for this energy was by Fritze and Kennett who, in 1962, determined it to be 3.0 +0.1 MeV (7). This latest value for the decay energy was reported in the compilation by Wapstra and Gove. The discrepancies in the reported measurements of this particular beta decay energy present a need to remeasure this energy in order to resolve this issue. 140 l4l 142 In addition, the decay energies of Xe, Cs, and Cs were pre­ dicted to be 4.3, 5.1, and 6.7 MeV by Wapstra and Gove (2). In this pre­ diction, they required simultaneous smoothness of two-neutron separation energies, two-proton separation energies, alpha-decay energies and beta- decay energies for their estimation, using the method developed by Way 3 and Wood (2,8). This method makes use of the prediction (derived from the semi-empirical mass formula of Von Weisaecker) that the beta decay energy varies approximately linearly with N, the neutron number, if either A, I (=N - Z) or Z is held constant (8). This linear dependence is illustrated in Figure 1 for the mass region around A = 108, where the values for the beta decay energies have been taken from the compilation of Wapstra and Gove. The deviation from linearity is most pronounced in mass regions near either shell closure or nuclear deformation. The beta decay energies measured in this work were compared with two mass formulas or laws: 1) the liquid drop model semi-empirical mass law developed by Von Weisaecker and expanded to include shell effects and BCS theory pairing energies by P. Seeger (9); and 2) the isospin-based mass relation developed by Garvey e^ a1^. (10). All mass formulas are semi- empirical in nature, that is, the values for the parameters that make up the formulas are determined using experimental results. Since the majority of the available data come from the "near-stable" nuclei, the mass formulas are most accurate in this region. These mass formulas are often used to predict properties of nuclei In regions not accessible by experiment and sometimes far removed from stability. An example of this Is reported by P. Seeger (9) in his discussion of the "r-process" of nucleogenesis. Knowledge of the masses in the extreme "neutron-rich" region far from the line of beta stability is desired to extract the con­ ditions (temperature, neutron flux, etc.) that are necessary to sustain the 'V-procesb.'' Sccyci usas several fcrzulcc to predict the relative isotopic abundances resulting from this process. Of all the formulas he 4 -4 -6- -7 64 66 N Figure 1.
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