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EXPERIMENTAL AND COMPUTATIONAL STUDIES OF NONLINEAR QUENCHING IN MATERIALS USED AS RADIATION DETECTORS

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title
EXPERIMENTAL AND COMPUTATIONAL STUDIES OF NONLINEAR QUENCHING IN MATERIALS USED AS RADIATION DETECTORS
author
Grim, Joel Q.
abstract
The next generation of radiation detectors used in security scanning, medical imaging, and high energy physics applications depend on understanding the physical mechanisms that limit intrinsic energy resolution. Nonproportionality between electron energy response and the initial energy of a stopping electron is a significant cause of the degradation of energy resolution. The physical origin of nonproportional response is generally regarded to start with nonlinear quenching, proportional to 2nd or 3rd power of local excitation density. A large part of the present work is the experimental determination of the important physical parameters governing nonproportional response. To that end, both the magnitude and kinetic order of nonlinear quenching rates have been determined using an above-gap z-scan technique in materials ranging from halides such as CsI:Tl and SrI2:Eu, to oxides and semiconductors. It is shown that the kinetic order of nonlinear quenching has direct consequences on scintillator light yield and proportionality. Furthermore, 2nd order quenching indicates the carrier population is dominated by bound electrons and holes (excitons or self-trapped excitons), and 3rd order quenching implies free carriers. A population of free carriers or bound electrons and holes has consequences beyond the difference in light yield and proportionality that result from pure 2nd or 3rd order quenching. For example, in halides with self-trapped holes, the mobile electrons can move away from the dense core of holes thus escaping nonlinear quenching. Coupled with calculations of hot electron group velocity, we have used this information to explain why NaI:Tl and SrI2:Eu have better proportionality and light yield than oxides and flourides, as well as why SrI2:Eu has better light yield and proportionality than NaI:Tl.
subject
Geant4
Monte Carlo simulations
Radiation detector materials
Scintillator nonproportionality
Ultra-fast optics
contributor
Williams, Richard T. (committee chair)
Bourland, J. Daniel (committee member)
Holzwarth, Natalie (committee member)
Carroll, David (committee member)
Ucer, Kamil B. (committee member)
date
2012-09-05T08:35:20Z (accessioned)
2013-09-05T08:30:10Z (available)
2012 (issued)
degree
Physics (discipline)
embargo
2013-09-05 (terms)
identifier
http://hdl.handle.net/10339/37441 (uri)
language
en (iso)
publisher
Wake Forest University
type
Dissertation

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