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Improving the Scintillation Performance of Ksr2i5:Ce3+ Through Exploration of Activator Concentration and Growth Conditions

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Improving the Scintillation Performance of Ksr2i5:Ce3+ Through Exploration of Activator Concentration and Growth Conditions University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 5-2019 Improving the Scintillation Performance of KSr2I5:Ce3+ through Exploration of Activator Concentration and Growth Conditions Eleanor Paige Comer University of Tennessee, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Recommended Citation Comer, Eleanor Paige, "Improving the Scintillation Performance of KSr2I5:Ce3+ through Exploration of Activator Concentration and Growth Conditions. " Master's Thesis, University of Tennessee, 2019. https://trace.tennessee.edu/utk_gradthes/5414 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Eleanor Paige Comer entitled "Improving the Scintillation Performance of KSr2I5:Ce3+ through Exploration of Activator Concentration and Growth Conditions." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Nuclear Engineering. Charles L. Melcher, Major Professor We have read this thesis and recommend its acceptance: Mariya Zhuravleva, Eric Lukosi Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Improving the Scintillation Performance of KSr2I5:Ce3+ through Exploration of Activator Concentration and Growth Conditions A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Eleanor Paige Comer May 2019 Copyright © 2019 by Eleanor P. Comer All rights reserved. ii ACKNOWLEDGEMENTS This work was supported by Siemens Medical Solutions and the US Department of Homeland Security’s Domestic Nuclear Detection Office under grant #2012- DN-077-ARI067-04. This support does not constitute an expressed or implied endorsement on the part of the Government. To my advisor, Dr. Chuck Melcher, thank you first and foremost for providing me the opportunity to further my education. I will forever be grateful for this opportunity to work for you and learn from you. Without your leadership and kindhearted nature, I don’t think our research group would have the same respectful and supportive atmosphere that has allowed me to freely ask questions or to learn as much as I have from my peers. To my other committee members, Dr. Mariya Zhuravleva and Dr. Eric Lukosi, thank you for your time and efforts spent supporting this research, both prior and current. It is greatly appreciated and wouldn’t have been possible without you both. To my research group, The Scintillation Materials Research Center, I could not have done anything without everyone’s support. In particular, Dr. Luis Stand, thank you for the immense amount of guidance you have given me to get me started on this project and helping me to correct and learn from all the many mistakes I’ve made along the way. Camera Foster and Kaycee Gass, my female peers and friends, you are amazing and I am eternally grateful for your presence and willingness to listen and offer support when I needed it. Josh Smith, Cordell Delzer, Matt Lloyd, Matheus Pianassola, and Daniel Rustrom - big thanks to all of you guys for your friendship and all the help you’ve given me. I’m grateful for all of you for putting up with me for the past couple years. Additionally, Merry Koschan and Dr. Yuntau Wu, thank you both for sharing your experience and for your input and guidance. To Dr. Lynn Boatner, thank you for providing me the incredible opportunity to work with you at ORNL. You taught me so much about how to do research and how to work in a lab. Your encouragement to pursue graduate education in the first place is something that I am very grateful for. To the late Dr. Graham Walford, whom I was unable to work with as much as planned due to his unexpected passing, your guidance and encouragement is not forgotten. May you rest in peace. And finally, to my family, thank you for everything. iii ABSTRACT Potassium strontium iodide (KSr2I5 or KSI) has been previously discovered and investigated as a high energy resolution scintillator for national security applications. Activators were investigated in hopes to improve some of the less desirable characteristics associated with typical Eu2+-doping, like decay time and slightly higher emission wavelength. Cerium-3+ was identified as one of the most promising alternatives, but challenges with crystal growth and poor crystal quality have made investigation more challenging due to an inability to obtain high quality single crystals. A series of KSr2I5:Ce crystals with varying concentrations of Ce3+ were grown and characterized via the Bridgman-Stockbarger method for the purpose of this research. Crystal quality was noticeably improved after investigation into interface control parameters and adjusting the thermal gradient in the growth furnace. Other experiments were conducted to investigate further improvements in crystal quality, specifically at higher Ce-dopant concentrations. The maximum achievable scintillation performance of each crystal was measured 3 with small samples (0.5 - 1 cm ). Light yields of all KSr2I5:Ce have been consistent, achieving up to 50,000 photons/MeV. Energy resolution values as low as 3.1% at 662 keV have also been observed and appear to be loosely correlated to Ce3+-concentration and overall crystal quality. Other factors contributing to energy resolution of scintillators and the overall performance of grown crystals are discussed in relation to applicability for security applications. iv TABLE OF CONTENTS Chapter One : Introduction and Motivation ............................................................ 1 Security Needs ................................................................................................... 1 Scintillation ......................................................................................................... 2 Scintillators ..................................................................................................... 2 Scintillation Mechanism .................................................................................. 2 Chapter Two : Background and Literature Review ................................................ 8 Halides ............................................................................................................... 8 Metal Halides .................................................................................................. 8 Ternary Halides .............................................................................................. 9 Potassium Strontium Iodide ............................................................................... 9 KSr2I5 .............................................................................................................. 9 Ce3+ vs. Eu2+ Doping .................................................................................... 12 Chapter Three : Experimental Methods ............................................................... 14 Crystal Growth .................................................................................................. 14 The Bridgman-Stockbarger Method ............................................................. 14 Specific Crystal Growth Procedures ............................................................. 14 Thermal Profile Calculations ......................................................................... 16 Characterization ............................................................................................... 17 Energy Resolution ........................................................................................ 18 Absolute Light Output ................................................................................... 18 Nonproportionality ........................................................................................ 18 Scintillation Decay Time ............................................................................... 19 Radioluminescence ...................................................................................... 19 Chapter Four : Results and Discussion ............................................................... 20 Crystal Growth .................................................................................................. 20 Interface Consideration ................................................................................ 20 Initial Crystal Growths ................................................................................... 21 Crystal Grows after Manipulation of Thermal Gradient ................................ 25 Melt Filtering Experiments ............................................................................ 25 Summary of all Crystal Growths ................................................................... 29 Scintillation Properties ...................................................................................... 29 Best-Achieved Energy Resolution ................................................................ 29 Energy Resolution at Low Ce-concentrations .............................................. 32 Additional
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