Clemson University TigerPrints All Theses Theses 12-2014 FAST FISSION NEUTRON DETECTION USING THE CHERENKOV EFFECT Matthew iM llard Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_theses Part of the Environmental Engineering Commons, Nuclear Engineering Commons, and the Physics Commons Recommended Citation Millard, Matthew, "FAST FISSION NEUTRON DETECTION USING THE CHERENKOV EFFECT" (2014). All Theses. 2047. https://tigerprints.clemson.edu/all_theses/2047 This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorized administrator of TigerPrints. For more information, please contact [email protected]. FAST FISSION NEUTRON DETECTION USING THE CHERENKOV EFFECT A Thesis Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Master of Science Environmental Engineering and Earth Science by Matthew James Millard December 2014 Accepted by: Timothy A. DeVol, Committee Chair Zane W. Bell Lindsay Shuller-Nickles ABSTRACT The Cherenkov effect in optically clear media of varying indices of refraction and composition was investigated for quantification of fast neutrons. The ultimate application of the proposed detection system is criticality monitoring. The optically clear medium, composed of select target nuclei, was coupled to a photomultiplier tube. Neutron reaction products of the target nuclei contained within the optical medium emit beta particles and gamma rays that produce Cherenkov photons within the medium which can be detected. Assessed media include quartz (SiO2), sapphire (Al2O3), spinel (MgAl2O4), and zinc sulfide (ZnS), which were irradiated with un-moderated 252Cf. Monte Carlo N-Particle (MCNP) code simulations were conducted to quantify the neutron flux incident on the media. High resolution gamma-ray spectroscopic measurements of the samples were conducted to verify the MCNP estimate. The threshold reactions of interest were 28Si (n, p) 28Al, 27Al (n, p) 27Mg, 24Mg(n, p)24Na, and 64Zn(n, p)64Cu which have neutron reaction cross sections in the 1 to 10 MeV range on the order of 0.1 barn. The detection system offers a unique way to measure a criticality event; it can count in place, making retrieval by emergency personnel unnecessary. ii ACKNOWLEDGEMENTS Thanks go to: Dr. Timothy DeVol, for taking a chance and hiring me as one of his students (I promise it will pay off some day). Without his guidance, this research would not have been possible. Dr. Lindsay Shuller-Nickles, for teaching me about the nuclear fuel cycle, giving me her input and words of encouragement throughout this process, and lending me books that I will likely never return. Dr. Zane Bell, for developing this detection technique, allowing me to work with him at ORNL, showing me how interesting scientific research can be, and most importantly, for teaching me how to build match stick rockets. Dr. Lynn Boatner, for developing this detection technique with Dr. Bell and creating the glass that I worked with at ORNL. Dr. John Ballato, for introducing me to the idea of using crystal samples. Amy Meldrum, for helping me learn how to use GATE software. Dr. Elizabeth Carraway, for allowing me to use her spectrofluorometer. My friends, for making every day a little better. iii TABLE OF CONTENTS Page ABSTRACT ........................................................................................................................................................................................ ii ACKNOWLEDGEMENTS ............................................................................................................................................................ iii LIST OF FIGURES .......................................................................................................................................................................... vi LIST OF TABLES ............................................................................................................................................................................ ix INTRODUCTION ............................................................................................................................................................................. 1 BACKGROUND................................................................................................................................................................................. 3 Nuclear Criticality Accidents ............................................................................................................................................... 3 Nuclear Accident Dosimetry ................................................................................................................................................ 5 THEORY ............................................................................................................................................................................................. 9 Cherenkov Radiation............................................................................................................................................................... 9 Neutron Activation................................................................................................................................................................. 12 Recent Research ...................................................................................................................................................................... 14 Preliminary Data ................................................................................................................................................................ 16 Target Material Properties ................................................................................................................................................. 18 1) Shape of the Cross Section ................................................................................................................................. 18 2) Magnitude of the Cross Section ....................................................................................................................... 18 3) Decay Constant of the Induced Activity ....................................................................................................... 19 4) Purity and Interfering Activities ..................................................................................................................... 19 5) Nature of the Induced Activity ......................................................................................................................... 20 6) Physical Properties ............................................................................................................................................... 20 RESEARCH OBJECTIVE ............................................................................................................................................................. 22 Hypotheses ................................................................................................................................................................................ 22 MATERIALS AND METHODS .................................................................................................................................................. 23 Target Nuclides........................................................................................................................................................................ 23 Ideal Media ................................................................................................................................................................................ 25 Neutron Source ........................................................................................................................................................................ 26 Procedure ................................................................................................................................................................................... 27 Fluorescence Discrimination ........................................................................................................................................ 27 Irradiation ............................................................................................................................................................................. 31 iv TABLE OF CONTENTS (CONTINUED) Page LLD and ULD ........................................................................................................................................................................ 33 Time Series Measurements ........................................................................................................................................... 34 Calculating Efficiency ....................................................................................................................................................... 35 Simulations ................................................................................................................................................................................ 36 RESULTS AND DISCUSSION .................................................................................................................................................... 38 Experimental Half-Life ........................................................................................................................................................