Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators

Journal Article · Sun Jul 01 00:00:00 EDT 2012 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4736088· OSTI ID:22089308

Zhiguo, Wang; Fei, Gao; Kerisit, Sebastien ^[1]; Yulong, Xie ^[2]; Campbell, Luke W. ^[3]

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1. Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
2. Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
3. National Security Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF{sub 2} and BaF{sub 2}. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF{sub 2}, BaF{sub 2}, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs{sup +} relative to Na{sup +}, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

• OSTI ID: 22089308
• Journal Information: Journal of Applied Physics, Vol. 112, Issue 1; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BARIUM FLUORIDES
CALCIUM FLUORIDES
CESIUM COMPOUNDS
CESIUM IODIDES
CESIUM IONS
COMPUTERIZED SIMULATION
DISTRIBUTION
DOPED MATERIALS
ELECTRIC FIELDS
MEAN FREE PATH
MONTE CARLO METHOD
PERMITTIVITY
PROBABILITY
RECOMBINATION
SODIUM IODIDES
SODIUM IONS
SOLID SCINTILLATION DETECTORS
THALLIUM
THERMALIZATION
TRAPPING