@article{holmes_calderon_peeples_gardner_2011, title={A proposed benchmark problem for cargo nuclear threat monitoring}, volume={652}, ISSN={["0168-9002"]}, DOI={10.1016/j.nima.2010.10.070}, abstractNote={There is currently a great deal of technical and political effort focused on reducing the risk of potential attacks on the United States involving radiological dispersal devices or nuclear weapons. This paper proposes a benchmark problem for gamma-ray and X-ray cargo monitoring with results calculated using MCNP5, v1.51. The primary goal is to provide a benchmark problem that will allow researchers in this area to evaluate Monte Carlo models for both speed and accuracy in both forward and inverse calculational codes and approaches for nuclear security applications. A previous benchmark problem was developed by one of the authors (RPG) for two similar oil well logging problems (Gardner and Verghese, 1991, [1]). One of those benchmarks has recently been used by at least two researchers in the nuclear threat area to evaluate the speed and accuracy of Monte Carlo codes combined with variance reduction techniques. This apparent need has prompted us to design this benchmark problem specifically for the nuclear threat researcher. This benchmark consists of conceptual design and preliminary calculational results using gamma‐ray interactions on a system containing three thicknesses of three different shielding materials. A point source is placed inside the three materials lead, aluminum, and plywood. The first two materials are in right circular cylindrical form while the third is a cube. The entire system rests on a sufficiently thick lead base so as to reduce undesired scattering events. The configuration was arranged in such a manner that as gamma-ray moves from the source outward it first passes through the lead circular cylinder, then the aluminum circular cylinder, and finally the wooden cube before reaching the detector. A 2 in.×4 in.×16 in. box style NaI (Tl) detector was placed 1 m from the point source located in the center with the 4 in.×16 in. side facing the system. The two sources used in the benchmark are 137Cs and 235U.}, number={1}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Holmes, Thomas Wesley and Calderon, Adan and Peeples, Cody R. and Gardner, Robin P.}, year={2011}, month={Oct}, pages={52–57} }
 @article{wang_calderon_peeples_ai_gardner_2011, title={Monte Carlo investigation and optimization of coincidence prompt gamma-ray neutron activation analysis}, volume={652}, ISSN={["1872-9576"]}, DOI={10.1016/j.nima.2010.08.011}, abstractNote={Normal Prompt Gamma-Ray Neutron Activation Analysis (PGNAA) suffers from a large inherent noise or background. The coincidence PGNAA approach is being investigated for eliminating almost all of the interfering backgrounds and thereby significantly improving the signal-to-noise ratio (SNR). This can be done since almost all of the prompt gamma rays from elements of interest are emitted in coincidence except hydrogen. However, it has been found previously that while the use of two normal NaI detectors greatly reduces the background, the signal is also greatly reduced so that very little improvement in standard deviation is obtained. With the help of MCNP5, the general-purpose Monte Carlo N-Particle code, and CEARCPG, the specific purpose Monte Carlo code for Coincidence PGNAA, further optimization of the proposed coincidence system is being accomplished. The idea pursued here is the use of a large area plastic scintillation detector as the trigger for coincidence events together with a normal large NaI detector. In this approach the detection solid angle is increased greatly, which directly increases the probability of coincidence detection. The 2D-coincidence spectrum obtained can then be projected to the axis representing the NaI detector to overcome the drawback of low energy resolution and photopeak intensity of the plastic scintillation detector and utilize the overall higher coincidence counting rate. To reach the best coincidence detection, the placement of detectors, sample, and the moderator of the neutron source have been optimized through Monte Carlo simulation.}, number={1}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Wang, Jiaxin and Calderon, Adan and Peeples, Cody R. and Ai, Xianyun and Gardner, Robin P.}, year={2011}, month={Oct}, pages={572–577} }
 @article{gardner_ai_peeples_wang_lee_peeples_calderon_2011, title={Use of an iterative convolution approach for qualitative and quantitative peak analysis in low resolution gamma-ray spectra}, volume={652}, ISSN={["0168-9002"]}, DOI={10.1016/j.nima.2010.12.224}, abstractNote={In many applications, low resolution gamma-ray spectrometers, such as sodium iodide scintillation detectors, are widely used primarily due to their relatively low cost and high detection efficiency. There is widespread interest in improved methods for analyzing spectral data acquired with such devices, using inverse analysis. Peak means and peak areas in gamma- and X-ray spectra are needed for both qualitative and quantitative analysis. This paper introduces the PEAKSI code package that was developed at the Center for Engineering Applications of Radioisotopes (CEAR). The basic approach described here is to use accurate forward models and iterative convolution instead of direct deconvolution. Rather than smoothing and differentiation a combination of linear regression and non-linear searching is used to minimize the reduced chi-square, since this approach retains the capability of establishing uncertainties in the estimated peak parameters. The PEAKSI package uses a Levenberg–Marquardt (LM) non-linear search method combined with multiple linear regression (MLR) to minimize the reduced chi-square value for fitting single or multiple overlapping peaks to determine peak parameters, including peak means, peak standard deviations or full width at half maximum (FWHM), net peak counts, and background counts of peaks in experimental gamma-ray spectra. This approach maintains the natural error structure so that parameter uncertainties can be estimated. The plan is to release this code to the public in the near future.}, number={1}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Gardner, Robin P. and Ai, Xianyun and Peeples, Cody R. and Wang, Jiaxin and Lee, Kyoung and Peeples, Johanna L. and Calderon, Adan}, year={2011}, month={Oct}, pages={544–549} }
 @article{peeples_mickael_gardner_2010, title={On replacing Am-Be neutron sources in compensated porosity logging tools}, volume={68}, ISSN={["0969-8043"]}, DOI={10.1016/j.apradiso.2009.11.042}, abstractNote={Authors explored the direct replacement of Am-Be neutron sources in neutron porosity logging tools through Monte Carlo simulations using MCNP5. (252)Cf and electronic accelerator neutron sources based on the Deuterium-Tritium fusion reaction were considered. Between the sources, a tradeoff was noted between sensitivity to the presence of hydrogen and uncertainty due to counting statistics. It was concluded that both replacement sources as well as accelerator sources based on the Deuterium-Deuterium fusion reaction warrant further consideration as porosity log sources.}, number={4-5}, journal={APPLIED RADIATION AND ISOTOPES}, author={Peeples, Cody R. and Mickael, Medhat and Gardner, Robin P.}, year={2010}, pages={926–931} }