Using Ultrafast Laser Pulses and Computational Modeling to Understand Nonproportionality in Spectroscopic Gamma-Ray Detectors
Under gamma-ray or charged-particle excitation, scintillation light yield is a complicated function of carrier diffusion and cooling in the track along with kinetic rate terms depending on local excitation density. Up to 1021 electron-hole pairs/cm3 are produced in an initial track radius of about 3 nm. Extracting the fundamental rate constants directly from such conditions would require solving the diffusion and cooling problems in complex track structures first. Laser interband photon density response and time-resolved pump-probe studies are surrogate experiments that allow measuring nonlinear response terms, the time sequence of carrier capture, and some capture rate constants without the spatial complexity of particle tracks. Then the track structure, hot electron cooling, self-trapping, diffusion, and electric currents can be built back in by numerical modeling to compare with gamma detection performance. The result that is sought is a predictive model of scintillator proportionality and resolution based on independently measured material parameters.