Coupled Rate and Transport Equations Modeling Light Yield, Pulse Shape, and Proportionality to Energy in Electron Tracks: A Study of CsI and CsI:Tl Scintillators

This dissertation reports on development and testing of a scintillation response model of progressive comprehensiveness that computes emission intensity over time and space in electron tracks by solving coupled rate and transport equations describing both the movement and the linear and nonlinear interactions of the charge carriers deposited along the ionization track. The tracks are initially very narrow before hot and thermalized carrier diffusion takes effect. This suggests that an adequate and computationally manageable representation may be obtained by modeling diffusion in one dimension, the radius. The initial track resulting from Monte Carlo simulations by \ac{GEANT4} or \ac{NWEGRIM} codes is numerically chopped into cells small enough to approximate their ionization density as constant, and these form the individual parts of a finite element model. The initial ionization density values vary from cell to cell along the length of the track with the variation in \emph{dE/dx} and we calculate the light yield for each local value of \emph{dE/dx}. This intermediate quantity that we call local light yield as a function of dE/dx cannot itself be directly measured by experiments. The local light yields must be multiplied by the number of times the associated ionization density occurs in repeated Monte Carlo simulations for the given initial electron energy, and then the yields are summed to report the total light yield. When this calculation is carried out over a range of energies the results give the predicted electron energy response or proportionality curve as a function of initial electron energy, for comparison to Compton-coincidence and K-dip experiments. This has been done in the present work for CsI at 295 K and 100K, and for CsI:Tl at 295 K.

Grantor dc:publisher

Wake Forest University

Year dc:date.issued

2016

Author dc:creator

• Lu, Xinfu

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/10339/64187

OAI identifier oai:identifier

oai:wakespace.lib.wfu.edu:10339/64187