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WFU Physics PhD Thesis Presentation

TITLE: Toward a User's Toolkit for Modeling Scintillator Proportionality and Light Yield

SPEAKER: Qi Li,

Department of Physics
Wake Forest University

TIME: Thursday May 1, 2014 at 1:00 PM

PLACE: Room 103 Olin Physical Laboratory


All interested persons are cordially invited to attend.

ABSTRACT

Intrinsic nonproportionality is a material dependent phenomenon that sets an ultimate limit on energy resolution of radiation detectors. In general, anything that causes light yield to change along the particle track (e.g., the primary electron track in γ-ray detectors) contributes to nonproportionality. Most of the physics of nonproportionality lies in the host-transport and transfer-to-activator term. The main physical phenomena involved are carrier diffusion, trapping, drift in internal electric fields, and nonlinear rates of radiative and nonradiative recombination. Some complexity is added by the now well-established fact that the electron temperature is changing during important parts of the physical processes listed above. It has consequences, but is tractable by application of electron-phonon interaction theory and first-principles calculation of trap structures checked by experiment. Determination of coefficients and rate "constants" as functions of electron temperature Te for diffusion, D(Te(t)); capture on multiple radiative and nonradiative centers, A1i(Te(t)); bimolecular exciton formation, B2(Te(t)); and nonlinear quenching, K2(Te(t)), K3(Te(t)) in specific scintillator materials will enable computational prediction of energy-dependent response from standard rate equations solved in the electron track for initial excitation distributions calculated by standard methods such as Geant4. Te(t) itself is a function of time. Determination of these parameters can be combined with models describing carrier transport in scintillators, which is able to build a userr's toolkit for analyzing any existing and potential scintillators. In the dissertation, progress in calculating electronic structure of traps & activators, diffusion coefficients and rate functions, and testing the model will be described.



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