Ph.D. Thesis Defense by Wondwosen Mengesha
Friday, May 3, 2002

(Dr. John D. Valentine, advisor)

"NaI(Tl) Electron Energy Resolution"

Abstract

A technique for characterizing scintillator total electron energy resolution he,tot is proposed. Based on the measured he,tot results, the total photon energy resolution of NaI(Tl) is computationally determined and subsequently compared to measured data to validate the technique. The he,tot method is based on a modification of the Compton Coincidence Technique (CCT), originally developed by Rooney & Valentine to characterize NaI(Tl) light yield nonproprtionality. Electron energy resolution measurements are made using variable solid angle collimation of photons that are scattered from a primary NaI(Tl) detector and are incident on a secondary high purity germanium detector. These measurements enable estimation of the total electron energy resolution he,tot for monoenergetic electrons which is a fundamental characteristic of scintillation detectors.

A method for determining the nonproportionality component of scintillator energy resolution hg,non was previously developed by Valentine, Rooney & Li. hg,non is due to nonproportionality and variation in the number and energy of primary and secondary electrons in scintillators. The he,tot results from this study will be convolved with this calculated hg,non to determine total photon energy resolution hg,tot. Finally, he,tot results will enable NaI(Tl) intrinsic gamma and intrinsic electron energy resolutions to be determined by deconvolving photomultiplier and associated electronic components. To consolidate experimental results, a theoretical approach will be used to calculate the intrinsic gamma and intrinsic electron energy resolutions. Previous models proposed by other groups for electron energy loss process and electron hole migration will be implemented and evaluated in the calculation. In addition, hybrids of these models and alternative models will be evaluated.