Experimental and computational results on exciton/freecarrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality
Abstract
Models of nonproportional response in scintillators have highlighted the importance of parameters such as branching ratios, carrier thermalization times, diffusion, kinetic order of quenching, associated rate constants, and radius of the electron track. For example, the fraction ηeh of excitations that are free carriers versus excitons was shown by Payne and coworkers to have strong correlation with the shape of electron energy response curves from Comptoncoincidence studies. Rate constants for nonlinear quenching are implicit in almost all models of nonproportionality, and some assumption about track radius must invariably be made if one is to relate linear energy deposition dE/dx to volumebased excitation density n (eh/cm3) in terms of which the rates are defined. Diffusion, affecting timedependent track radius and thus density of excitations, has been implicated as an important factor in nonlinear light yield. Several groups have recently highlighted diffusion of hot electrons in addition to thermalized carriers and excitons in scintillators. However, experimental determination of many of these parameters in the insulating crystals used as scintillators has seemed difficult. Subpicosecond laser techniques including interband z scan light yield, fluencedependent decay time, and transient optical absorption are now yielding experimental values for some of the missing rates and ratios neededmore »
 Authors:
 Publication Date:
 Research Org.:
 Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1130729
 Report Number(s):
 PNNLSA99335
NN2001000
 DOE Contract Number:
 AC0576RL01830
 Resource Type:
 Conference
 Resource Relation:
 Conference: Hard XRay, GammaRay, and Neutron Detector Physics XV, August 25, 2013, San Diego, California. Proceedings of the SPIE, 8852:Paper No. 88520J
 Country of Publication:
 United States
 Language:
 English
Citation Formats
Williams, Richard, Grim, Joel, Li, Qi, Ucer, K. B., Bizarri, G. A., Kerisit, Sebastien N., Gao, Fei, Bhattacharya, Pijush, Tupitsyn, Eugene, Rowe, Emmanuel, Buliga, Vladimir M., and Burger, Arnold. Experimental and computational results on exciton/freecarrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality. United States: N. p., 2013.
Web. doi:10.1117/12.2027716.
Williams, Richard, Grim, Joel, Li, Qi, Ucer, K. B., Bizarri, G. A., Kerisit, Sebastien N., Gao, Fei, Bhattacharya, Pijush, Tupitsyn, Eugene, Rowe, Emmanuel, Buliga, Vladimir M., & Burger, Arnold. Experimental and computational results on exciton/freecarrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality. United States. doi:10.1117/12.2027716.
Williams, Richard, Grim, Joel, Li, Qi, Ucer, K. B., Bizarri, G. A., Kerisit, Sebastien N., Gao, Fei, Bhattacharya, Pijush, Tupitsyn, Eugene, Rowe, Emmanuel, Buliga, Vladimir M., and Burger, Arnold. 2013.
"Experimental and computational results on exciton/freecarrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality". United States.
doi:10.1117/12.2027716.
@article{osti_1130729,
title = {Experimental and computational results on exciton/freecarrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality},
author = {Williams, Richard and Grim, Joel and Li, Qi and Ucer, K. B. and Bizarri, G. A. and Kerisit, Sebastien N. and Gao, Fei and Bhattacharya, Pijush and Tupitsyn, Eugene and Rowe, Emmanuel and Buliga, Vladimir M. and Burger, Arnold},
abstractNote = {Models of nonproportional response in scintillators have highlighted the importance of parameters such as branching ratios, carrier thermalization times, diffusion, kinetic order of quenching, associated rate constants, and radius of the electron track. For example, the fraction ηeh of excitations that are free carriers versus excitons was shown by Payne and coworkers to have strong correlation with the shape of electron energy response curves from Comptoncoincidence studies. Rate constants for nonlinear quenching are implicit in almost all models of nonproportionality, and some assumption about track radius must invariably be made if one is to relate linear energy deposition dE/dx to volumebased excitation density n (eh/cm3) in terms of which the rates are defined. Diffusion, affecting timedependent track radius and thus density of excitations, has been implicated as an important factor in nonlinear light yield. Several groups have recently highlighted diffusion of hot electrons in addition to thermalized carriers and excitons in scintillators. However, experimental determination of many of these parameters in the insulating crystals used as scintillators has seemed difficult. Subpicosecond laser techniques including interband z scan light yield, fluencedependent decay time, and transient optical absorption are now yielding experimental values for some of the missing rates and ratios needed for modeling scintillator response. First principles calculations and Monte Carlo simulations can fill in additional parameters still unavailable from experiment. As a result, quantitative modeling of scintillator electron energy response from independently determined material parameters is becoming possible on an increasingly firmer data base. This paper describes recent laser experiments, calculations, and numerical modeling of scintillator response.},
doi = {10.1117/12.2027716},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2013,
month =
}

Models of nonproportional response in scintillators have highlighted the importance of parameters such as branching ratios, carrier thermalization times, diffusion, kinetic order of quenching, associated rate constants, and radius of the electron track. For example, the fraction ηeh of excitations that are free carriers versus excitons was shown by Payne and coworkers to have strong correlation with the shape of electron energy response curves from Comptoncoincidence studies. Rate constants for nonlinear quenching are implicit in almost all models of nonproportionality, and some assumption about track radius must invariably be made if one is to relate linear energy deposition dE/dx tomore »Cited by 6

Factors affecting estimation of the rate constants of the fluorodeoxyglucose (FDG) model from positron emission tomography (PET) data
A study has been performed of the factors affecting the statistical estimation of the rate constants of the FDG model from sequential PET scan data. The conditions under study are the effect of total data collection time and scan sampling rate on the accuracy of the estimates, the influence of vascular space in the tissue regionofinterest on the rate constants, the mathematical form of the fitting equation, the weighting of samples according to the total counts per scan (observation noise), and the intercorrelation of the parameter estimates. Plasma radioactivity samples and tomographic timeactivity curves collected from four normal volunteers onmore » 
Joint computational/experimental aerodynamics research on a reentry vehicle: Part 2, Computational results
Computational aerodynamics simulation applied to supersonic and hypersonic flight vehicles has significantly increased during the last several years. Flow field simulations have been computed for a wide variety of vehicles from ballistic reentry vehicles to the Space Shuttle. Although computational aerodynamics simulation has been taking more responsibility during this time, wind tunnel experimentation has continued to play the major role in flight vehicle analysis and design. This role, however, is changing because of the great strides in the capability and confidence in numerical simulations. In this paper computational results are obtained for a spherically blunted cone with a slice parallelmore » 
Experimental twonucleon spectroscopic factors. [Mixing ratio, relative normalization constants]
Since a similar shape of the form factors is a possible requirement for obtaining comparable results, using the /sup 28/Si(..cap alpha..,d)/sup 30/P data, for each L value (L = 0 to 6) a microscopic form factor with large amplitude was selected; and the (r,a) plane was searched for values where the positions of maxima, minima, and zerocrossings in the cluster form factor occur within a distance ..delta..R from the corresponding positions in the microscopic one. The mixing ratio and relative normalization constants for /sup 28/Si(..cap alpha..,d)/sup 30/P transitions calculated from shell model wave functions, the macroscopic fit to the calculatedmore » 
{lambda} and special elements for one, two and threedimensional singular problems in linear and nonlinear computational mechanics
This paper presents {lambda} element formulations for one, two, and threedimensional problems in computational mechanics. The first part of the paper discusses various alternatives of designing {lambda} elements for 1D problems with either known or unknown strength of singularities. This concept is further extended to 2D {lambda} elements for two dimensional problems by establishing a local r, {theta} coordinate system at the singularity and then considering 1D {lambda} element approximation in the r direction and pversion approximation in {Theta} direction (natural coordinate system) and then taking their products. The extension of 1D and 2D {lambda} element concepts for 3D problemsmore »