UNLV Theses, Dissertations, Professional Papers, and Capstones 8-2010 Neutron flux and energy characterization of a plutonium-beryllium isotopic neutron source by Monte Carlo simulation with verification yb neutron activation analysis Zachary R. Harvey University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Medicine and Health Sciences Commons, and the Nuclear Commons Repository Citation Harvey, Zachary R., "Neutron flux and energy characterization of a plutonium-beryllium isotopic neutron source by Monte Carlo simulation with verification by neutron activation analysis" (2010). UNLV Theses, Dissertations, Professional Papers, and Capstones. 900. http://dx.doi.org/10.34917/2242920 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Theses, Dissertations, Professional Papers, and Capstones by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. NEUTRON FLUX AND ENERGY CHARACTERIZATION OF A PLUTONIUM- BERYLLIUM ISOTOPIC NEUTRON SOURCE BY MONTE CARLO SIMULATION WITH VERIFICATION BY NEUTRON ACTIVATION ANALYSIS by Zachary R. Harvey Bachelor of Science Purdue University 2008 A thesis submitted in partial fulfillment of the requirements for the Master of Science in Health Physics Department of Health Physics and Diagnostic Sciences School of Allied Health Sciences Division of Health Sciences Graduate College University of Nevada, Las Vegas August 2010 Copyright by Zachary Harvey 2010 All Rights Reserved THE GRADUATE COLLEGE We recommend the thesis prepared under our supervision by Zachary R. Harvey entitled Neutron Flux and Energy Characterization of a Plutonium-Beryllium Isotopic Neutron Source by Monte Carlo Simulation with Verification by Neutron Activation Analysis be accepted in partial fulfillment of the requirements for the degree of Master of Science in Health Physics Health Physics and Diagnostic Sciences Ralf Sudowe, Committee Co-chair Phillip Patton, Committee Co-chair Gary Cerefice, Committee Member Patricia Paviett-Hartman, Graduate Faculty Representative Ronald Smith, Ph. D., Vice President for Research and Graduate Studies and Dean of the Graduate College August 2010 ii ABSTRACT Neutron Flux and Energy Characterization of a Plutonium-Beryllium Isotopic Neutron Source by Monte Carlo Simulation with Verification by Neutron Activation Analysis by Zachary Russel Harvey Dr. Ralf Sudowe, Committee Chair Assistant Professor of Health Physics University of Nevada, Las Vegas The purpose of this research was to characterize the neutron energy distribution and flux emitted from the UNLV plutonium-beryllium source, serial number MRC-N-W PuBe 453. This was accomplished through the use of the MCNPX/5 Monte-Carlo particle transport code to simulate radiation interactions within the physical environment of the source and its surroundings. The moderating drum currently containing the source as well as all of the sampling ports were accurately modeled in MCNPX/5. This geometry was then used to simulate the neutron interactions taking place in these geometries. The results of the simulations were then verified by the use of specifically chosen activation detectors and threshold foils designed to accurately convey information on the energy distribution and flux of the neutrons present at multiple sampling locations. iii TABLE OF CONTENTS ABSTRACT……………………………………………………………………………...iii LIST OF TABLES……………………………………………………………..…………vi LIST OF FIGURES……...……………………………………………………………....vii CHAPTER 1 INTRODUCTION...………………………………………………………1 Neutron Sources.........…....………………………………………………………..4 Monte Carlo Simulations…………………….……………………………............6 Neutron Activation .…...…………………...……………………………………..7 Activation Detector Materials………………...…………………………………...9 Literature Review………………………….....…………………………………..13 Scope of Work……………………………...……………………………………17 CHAPTER 2 MONTE CARLO………………….…………………………………….18 SOURCES4C….…………………………………………………………………18 MCNPX………………………………………………………………………….22 CHAPTER 3 NEUTRON ACTIVATION FOILS………………………...……………31 Theory………………………….………………………………………………...31 Materials & Methods………….…………………………………………………33 Counting Methods…………...…………………………………………………..35 Irradiation Scheme……….………………………………………………………36 CHAPTER 4 RESULTS & DISCUSSION…………………………………………….41 Gold (Au) Foil Irradiations………….…………………………………………...41 Indium (In) Foil Irradiations………….………………………………………….45 Error….……………………………....…………………………………………..52 CHAPTER 5 CONTINUATION OF RESEARCH…………………………………….54 Conclusion…...…………………………………………………………………..54 Future Research……...…………………………………………………………..54 APPENDIX 1 SOURCES4C DATA………………………………………………….....56 APPENDIX 2 MODERATING BARREL DIMENSIONS……………………………..59 APPENDIX 3 ACTIVATION CALCULATION DATA……………………………….60 APPENDIX 4 MCNPX DATA………………………………………………………….61 APPENDIX 5 MCNPX INPUT DECKS………………………………………………...68 BIBLIOGRAPHY………………………………………………………………………..75 iv VITA……………………………………………………………………………………..76 v LIST OF TABLES Table 1 Average Neutron Energies Originating at Source…..……….…...…………..5 Table 2 Materials Useful as Slow Neutron Activation Detectors…...……...………..11 Table 3 Input Radionuclide Compositions for SOURCES4C…..…………...……....20 Table 4 PUBE Source Outer Dimensions……………………………………...…….21 Table 5 Gold (Au) Neutron Reactions…………………………………………...…..34 Table 6 Indium (In) Neutron Reactions…………………………………………...…35 Table 7 Aluminum (Al) Threshold Reactions……………………………………......37 Table 8 Irradiation Scheme………………………………………………………......40 Table 9 Comparison of Activity and Flux of Au foils in CT position…………….....41 Table 10 Comparison of Activity and Flux of Au foils in 8 in position……………....44 Table 11 Comparison of Activity and Flux of In foils in CT position…………..….....46 Table 12 Comparison of Activity and Flux of In foils in Y position………………….48 Table 13 Comparison of Activity and Flux of In foils in 5in position……………...…50 Table 14 Metals Foils for Future Irradiation…………………………..........................55 vi LIST OF FIGURES Figure 2.1 UNLV Pu-Be Neutron Source…..…………………………………...….19 Figure 2.2 Comparison of SOURCES4C Results…..…………………………...….21 Figure 2.3 Histogram of Neutron Energy vs. Flux at the Source…..…………….....22 Figure 2.4 MCNPX Irradiation Geometry in X,Y Direction..………………………23 Figure 2.5 MCNPX Irradiation Geometry in X,Z Direction..……………………....24 Figure 2.6 MCNPX Irradiation Geometry in Y,Z Direction…..…………………....25 Figure 2.7 Flux vs. Energy Bin for All Sampling Ports by Location…..…………...26 Figure 2.8 Flux vs. Energy Bin for CT Position….…………………………………27 Figure 2.9 Flux vs. Energy Bin for 8in Position….…………………………………27 Figure 2.10 Flux vs. Energy Bin for 5in Position…...………………………………..28 Figure 2.11 Flux vs. Energy Bin for 2in Position…...………………………………..28 Figure 2.12 Flux vs. Energy Bin for Y Position…...………...………….…………....29 Figure 2.13 Comparison of Neutron Flux vs. Energy for Cd and Non-Covered Foil..30 Figure 3.1 Au-198 Decay Scheme….……………………………………………….34 Figure 3.2 Aluminum Activation Foil Sample Holder…..……………………….....37 Figure 4.1 Calc and Exp Thermal and Epi-Thermal Flux CT Position…..……...….42 Figure 4.2 Calc and Exp Thermal and Epi-Thermal Flux 8in Position…..……...….44 Figure 4.3 Calc and Exp Thermal, Epi-Thermal, Relativistic Flux for In CT Psn.....45 Figure 4.4 Calc and Exp Thermal, Epi-Thermal, Relativistic Flux for In Y Psn…...48 Figure 4.5 Calc and Exp Thermal, Epi-Thermal, Relativistic Flux for In 5in Psn….50 vii ACKNOWLEDGEMENTS I would like to thank Dr. Ralf Sudowe, coffee, and everyone else who helped me in the entirety of my thesis project. My parents deserve a special thank you for all of their support and encouragement throughout my entire education. I would also like to apologize to my parents for moving across the county following the completion of my education. viii CHAPTER 1 INTRODUCTION Neutron Interactions The discovery of neutrons dates back to 1931, when German scientists Walther Bothe and Herbert Becker found that if energetic alpha particles emitted from polonium collided with certain light elements, specifically beryllium, boron, or lithium, an unusually penetrating radiation was produced. Although it was mistaken for gamma radiation at the time, the two scientists had created the first man-made isotopic neutron source. In 1932, James Chadwick performed a series of experiments showing that the gamma ray hypothesis of Bothe and Becker was not possible. He suggested that the radiation consisted of an uncharged particle with approximately the same mass as a proton. Neutrons may be produced in several ways, such as: nuclear fission, nuclear fusion, accelerating devices that induce nuclear reactions involving charged particles and gamma-rays, and the interaction of alpha and gamma radiation with nuclei that results in neutron emission. Depending on how the neutrons are produced, their potential energy distribution ranges from a few tenths of eV to several GeV. However, due to the nature of this type of radiation the energy of the neutron produced at the source will most likely not be the energy of the particle that