Industrial Applications ofPhotonuclear Resonance Excitation by David Lee Chichester B,S' l Engineering Physics, University ofIllinois, 1993 M.S., Nuclear Engineering, University ofIllinois, 1995 SUBMITTED TO THE DEPARTMENT OF NUCLEAR ENGINEERlNG TN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF SCIENCE IN NUCLEAR ENGINEERlNG AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY SSAGHU Ens INSTITUTE June 2000 OF TECHNOLOGY [ APR 0 3 2003 ] © 2000 Massachusetts Institute ofTechnology All Rights Reserved LfaRARIES Signature of Author: . /"; Nuclear Engineering Department May 18,2000 Certified by: --~~:'=----::::< 7< Lawrence M. Lidsky Professor ofNuclear Engineering Thesis Supervisor Certified by: ~ Richard C. Lanza Senior Research cie tist, NUilear Engineering Department Thesis Reader Accepted by: Sow-Hsin Chen MASSACHUSETTSINST1TUTE~'; Professor ofNuclear Engineering OF TECHNOLOGY Chairman, Department Committee on Graduate Students {~~~J L'SRARIES Industrial Applications ofPhotonuclear Resonance Excitation by David Lee Chichester Submitted to the Department ofNuclear Engineering on May 15, 2000 in Partial Fulfillment ofthe Requirements for the Degree of Doctor ofScience in Nuclear Engineering ABSTRACT Photonuclear resonance excitation refers to a variety of photonuclear interaction processes that lead to the excitation ofa nucleus from some initial state to a higher energy nuclear state. Typical excited nuclear state lifetimes are short, ranging from nanoseconds to femtoseconds or less; however, some isotopes have unusually long-lived excited nuclear energy states, or isomers. This dissertation examines the feasibility of using bremsstrahlung irradiation sources to produce isomers for industrial applications. In contrast with charged particle based isomer production, the use of high energy photons allows for the irradiation and production of isomers in bulk materials. The commercial availability of reliable, high power industrial electron accelerators means that isomer activities sufficient for industrial applications may be achieved using bremsstrahlung, in contrast with neutron based approaches where suitable neutron sources of sufficient intensity for these applications are lacking. In order to design a system for creating nuclear isomers using photons, the resonant photon absorption isomeric excitation cross section must be known. Unlike neutron absorption and scattering cross sections, comparatively little infonnation exists for photon isomeric excitation. To address this, a theoretical model based upon statistical probability distributions of nuclear energy levels has been developed for calculating photon excitation cross sections at energies below neutron and proton binding energies; the ideal region of operation for most applications in order to minimize long term activation of materials. Isomeric excitation cross sections calculated using this technique have been compared with experimentally measured values and are found to agree to within a factor of two or better. Using this, a general transition equation suitable for both nuclear resonance fluorescence and isomer excitation has been developed for calculating nuclear level distribution probabilities for materials undergoing photon irradiation. Experiments have been carried out using an industrial 6 MeV electron accelerator to identify obstacles related to nuclear resonance fluorescence measurements as well as measurements of the decay of short-lived isomers using scintillators in the vicinity of high intensity bremsstrahlung sources. Use of a fast switching gating circuit in combination with a pulsed accelerator was found to be a satisfactory solution for dealing with problems related to the performance of a detectors photomultiplier tube as a result of exposure to scattered radiation during the beam pulse. Calculations have been carried out to assess the performance characteristics which could be expected from industrial photonuclear resonance excitation systems, based upon a 10 MeV electron accelerator. For simple isomer production, specific activities on the order of 1 mCi/gimA can be expected for irradiation periods sufficiently long for equilibrium to be reached. For the analysis of arsenic concentrations in environmental samples, sensitivities of 1 ± O. I ppm could be achieved using accelerator currents of 50 -I00 ~A with irradiations times of a few minutes or less. A system designed to analyze ore traveling along a conveyor belt could be used to sort gold ore based upon a lower grade cutoff of 5 ppm using an accelerator of 10 rnA with a processing volume exceeding 100 tons of ore per hour. Committee: L. M. Lidsky, Professor, Nuclear Engineering Department, MIT (Thesis Advisor) R. C. Lanza, Senior Research Scientist, Nuclear Engineering Department, MIT (Thesis Reader) P. Burstein, President, Skiametries, Inc. J. P. Freidberg, Professor, Nuclear Engineering Department, MIT J. Schweitzer, Professor, Physics Department, University ofConnecticut 4 ACKNOWLEDGMENTS Ofall the marvelous experiences and opportunities I have had at MIT since my arrival, I am most thankful for having had the good fortune ofmeeting my advisor Professor Larry Lidsky at the begilUling. I have never met anyone with both the breadth and depth ofknowledge Larry has in so many widely varying fields ofinterest. I am most inspired, however, by his ability to maintain such a healthy balance between family, work and life. Working on this thesis Larry's guidance was eagerly sought, freely given and always helpful. I feel fortunate to be able to refer to him as advisor, mentor and friend. Thank you. I came to MIT because ofRichard Lanza; thanks to his generosity and interest in this work, I stayed at MIT. During our short meeting together during my visit to the institute as a prospective graduate student in the spring of 1995 Dick's excitement for science and engineering were clearly evident. After working in his lab for the past two years, I now know that that first impression revealed only a glimpse ofhis unique drive and ingenuity for work in this field. It has been my good fortune to have had the opportunity to work with him on this dissertation and I can only hope that I will share his same enthusiasm for learning throughout my career. I would like to thank Dr. Paul Burstein, Professor JeffFreidberg and Professor Jeff Schweitzer, members ofmy committee. The time they took to read through this dissertation and their insightful comments and suggestions are greatly appreciated. I would like to thank all ofmy friends from Illinois, Ashdown and MIT, without whom I have no doubt I would never have done this. I would like to thank Brandon Blackburn and Jo O'Meara. I would like to thank Heather MacLean. Thanks, mom and dad. This research was funded in part through funds from the Office ofNational Drug Control Policy and the Federal Aviation Administration. 5 TABLE OF CONTENTS Acknowledgements 5 Table ofContents 7 List ofTables .' 10 List ofFigures 12 1 Introduction 19 2 Photonuclear Resonance Excitation Physics .27 2.1 PhotonucIear Interactions Primer 28 2.1.1 Background 28 2.1.2 Photon Induced Nuclear Excitation 31 2.1.2.1 Absorption 31 2.1.2.1.1 Resonance Interactions 32 2.1.2.1.1.1 Discrete Level Photon Absorption 32 2.1.2.1.1.2 Compound Nucleus Photon Absorption 34 2.1.2.1.1.2.1 Yttrium-89 41 2.1.2.1.1.2.2 Rhodium-l 03 42 2.1.2.1.1.2.3 Gold-197 44 2.1.2.1.1.2.4 Discussion 46 2.1.2.1.1.3 Stimulated Photon Emission .47 2.1.2.1.2 Non-Resonance Interactions .47 2.1.2.1.2.1 Inelastic Photoelectric Effect (lPE) Excitation .48 2.1.2.1.2.2 Nuclear Compton Effect (NCE) Excitation .48 2.1.2.1.2.3 Inelastic Pair Production (IPP) Excitation 50 2.1.2.2 Scattering 50 2.1.2.2.1 Nuclear Thompson (NT) Scattering 51 2.1.2.2.2 Nuclear Resonance 52 2.1.2.2.2.1 Fluorescence (F) Scattering 52 2.1.2.2.2.2 Giant Dipole Resonance (GDR) Scattering 53 2.1.2.2.2.3 Nuclear Raman (NRa) Scattering 54 2.1.2.2.3 Delbriick (D), Rayleigh (R) and Nuclear (or Internal) Compton (NC) Scattering 54 2.1.3 Nuclear De-Excitation and Photon Emission 55 54 2.2 Transition Model 55 2.2.1 Transition Mechanisms 56 2.2.1.1 Resonant Photon Absorption 56 2.2.1.2 Stimulated Isomeric Decay 57 2.2.1.3 Photonuclear Reactions 58 2.2.1.4 Natural Isomeric Decay 58 2.2.1.5 Nuclear Decay 58 2.2.2 The General Transition Equation 59 7 2.3 Calculation ofIsomeric Activity 60 2.3.1 Simplifications 60 2.3.2 Example Calculations 62 2.4 References 65 3 Industrial Implementation ofPRE 69 3.1 Isomers ~ 70 3.1.1 Characteristics 73 3.1.2 Previous Work 75 3.2 Radiation Source 78 3.2.1 Photon Radiation Sources 78 3.2.1.1 Isotopic - Discrete Energy 79 3.2.1.2 Isotopic - Continuous Energy 80 3.2.1.3 Nuclear Reactor - Discrete Energy 80 3.2.1.4 Nuclear Reactor - Continuous Energy 81 3.2.1.5 Accelerator - Discrete Energy 81 3.2.1.6 Accelerator - Continuous Energy 82 3.2.1.7 Comparison ofPhoton Sources 83 3.2.2 Bremsstrahlung Sources 85 3.2.2.1 X~ray Production and Calculation 85 3.2.2.2 Intensity 86 3.2.2.3 Flux 87 3.2.2.4 Sample Calculation 87 3.2.2.5 Timing 95 3.2.2.6 Reliability 96 3.2.2.7 Stability 96 3.2.2.8 Cost 96 3.3 Detection and Measurement System 97 3.3.1 Types ofInorganic Scintillators 99 3.3.2 Operational Parameters 102 3.3.2.1 Detection Efficiency 102 3.3.2.2 Light Properties: Light Yield & Wavelength 103 3.3.2.3 Decay Constant 103 3.3.2.4 Energy Resolution 103 3.3.2.5 Afterglow 104 3.3.2.6 Radiation Hardness 104 3.3.2.7 Stability 104 3.3.2.8 Price 105 3.3.3 Conclusions 105 3.4 References 106 4 Method Capabilities 111 4.1 Isomer Production 112