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Atanackovic J.,Chalk River Laboratories | Kramer G.H.,Human Monitoring Laboratory | Hogue M.,Savannah River Site
Applied Radiation and Isotopes | Year: 2013

An MCNP model of a pair of planar HPGe detectors (designated as: detector 3 and detector 4), that are used for routine lung counting at AECL, was developed. The model was benchmarked against experimental results, where a multi-line 152Eu source was counted in several different geometrical arrangements. The best agreement for both detectors was achieved when side and back dead layers (of both detectors) were quadrupled, with respect to the ones quoted by their manufacturer (Canberra). In the case of detector 4, the agreement between simulated and measured spectra was within 4%, throughout the whole γ-spectrum, spanning 70-1600keV. The same was true for detector 3 at the lower end of the γ-spectrum. However, at the high end of the γ-spectrum, the agreement was within 7% and 12% for 152Eu γ-lines at 778.9 and 1408.01keV. © 2013.

Kramer G.H.,University of Sussex | Hauck B.,Human Monitoring Laboratory
Health Physics | Year: 2012

A commercial detector calibration package has been assessed for its use to calibrate the Human Monitoring Laboratory's Portable Whole Body Counter that is used for emergency response. The advantage of such a calibration software is that calibrations can be derived very quickly once the model has been designed. The commercial package's predictions were compared to experimental point source data and to predictions from Monte Carlo simulations. It was found that the software adequately predicted the counting efficiencies of a point source geometry to values derived from Monte Carlo simulations and experimental work. Both the standing and seated counting geometries agreed sufficiently well that the commercial package could be used in the field. Copyright © 2012 Health Physics Society.

Martinez N.E.,Clemson University | Johnson T.E.,Colorado State University | Capello K.,Human Monitoring Laboratory | Pinder J.E.,Colorado State University
Journal of Environmental Radioactivity | Year: 2014

This study develops and compares different, increasingly detailed anatomical phantoms for rainbow trout (Oncorhynchus mykiss) for the purpose of estimating organ absorbed radiation dose and dose rates from 131I uptake in multiple organs. The models considered are: a simplistic geometry considering a single organ, a more specific geometry employing additional organs with anatomically relevant size and location, and voxel reconstruction of internal anatomy obtained from CT imaging (referred to as CSUTROUT). Dose Conversion Factors (DCFs) for whole body as well as selected organs of O.mykiss were computed using Monte Carlo modeling, and combined with estimated activity concentrations, to approximate dose rates and ultimately determine cumulative radiation dose (μGy) to selected organs after several half-lives of 131I. The different computational models provided similar results, especially for source organs (less than 30% difference between estimated doses), and whole body DCFs for each model (~3×10-3μGyd-1perBqkg-1) were comparable to DCFs listed in ICRP 108 for 131I. The main benefit provided by the computational models developed here is the ability to accurately determine organ dose. A conservative mass-ratio approach may provide reasonable results for sufficiently large organs, but is only applicable to individual source organs. Although CSUTROUT is the more anatomically realistic phantom, it required much more resource dedication to develop and is less flexible than the stylized phantom for similar results. There may be instances where a detailed phantom such as CSUTROUT is appropriate, but generally the stylized phantom appears to be the best choice for an ideal balance between accuracy and resource requirements. © 2014 Elsevier Ltd.

Ahmed A.S.,Human Monitoring Laboratory
Health physics | Year: 2011

This paper describes the methodology of measuring the chest wall thickness using the voxel image of the Lawrence Livermore National Lab (LLNL) torso phantom. The LLNL phantom is used as a standard to calibrate a lung counter consisting of a 2 × 2 array of germanium detectors. In general, an average thickness estimated from four counting positions is used as the chest wall thickness for a given overlay plate. For a given overlay, the outer chest surface differs from that of inner one, and the chest wall thickness varies from one position to other. The LLNL phantom with chest plate and C4 overlay plate installed was scanned with a CT (computed tomography) scanner. The image data, collected in DICOM (Digital Imaging and Communication) format, were converted to the MCNP input file by using the Scan2Mcnp program. The MCNP file was visualized and analyzed with the Moritz visual editor. An analytic expression was formulated and solved to calculate the chest wall thickness by using the point detector responses (F 5 tally of MCNP). To map the chest thickness, the entire chest wall was meshed into virtual grids of 1 cm width. A source and detector pair was moved along the inner and outer surface of the chest wall from right to left at different heights from neck to abdomen. For each height (z(k)), (x(i), y(j)) coordinates for the detector source pair were calculated from the visual editor and were scaled on-screen. For each (x(i), y(j), z(k)) position, a mesh thickness was measured from on-screen measurement and by solving the detector responses. The chest wall thicknesses at different positions on the outer surface of the chest were compared and verified using two methods.

Sabbir Ahmed A.,Human Monitoring Laboratory | H. Kramer G.,Human Monitoring Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

This study described the performance of an array of HPGe detectors, made by ORTEC. In the existing system, a metal end cap was used in the detector construction. In general, the natural metal contains some radioactive materials, create high background noises and signals during in vivo counting. ORTEC proposed a novel carbon fiber to be used in end cap, without any radio active content. This paper described the methodology of developing a model of the given HPGe array-detectors, comparing the detection efficiency and cross talk among the detectors using two end cap materials: either metal or carbon fiber and to provide a recommendation about the end cap material. The detectors counting efficiency were studied using point and plane sources. The cross talk among the array detectors were studied using a homogeneous attenuating medium made of tissue equivalent material. The cross talk was significant when single or multiple point sources (simulated to heterogeneous hot spots) were embedded inside the attenuating medium. With carbon fiber, the cross talk increased about 100% for photon energy at about 100 keV. For a uniform distribution of radioactive material, the cross talk increased about 510% when the end cap was made of carbon instead of steel. Metal end cap was recommended for the array of HPGe detectors. © 2011 Elsevier B.V.

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