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IEEE Symposium on nuclear Science (NSS/MIC)

作者： A.I. Hawari Jianwei Chen Bingjing Su Zhongxiang Zhao Nuclear and Radiological Engineering Program University of Cincinnati Cincinnati OH USA

An investigation was performed to assess the feasibility of passive gamma-ray spectrometry assay as an approach for on-line burnup determination for the Modular Pebble Bed Reactor (MPBR). In addition to its inherently safe design, a unique feature of this reactor is its multi-pass fuel cycle in which graphite fuel pebbles are randomly loaded and continuously cycled through the core until they reach their prescribed End-of-Life burnup limit (/spl sim/80,000 MWD/MTU). Therefore, unlike the situation with conventional light water reactors, depending solely on computational methods to perform in-core fuel management will be highly inaccurate. As a result, an on-line measurement approach becomes the only accurate method to assess whether a particular pebble has reached its End-of-Life burnup limit. The results of this investigation indicate that the fission products Cs-137 and Eu-154 provide accurate, and power-history-independent signatures that can be directly correlated with burnup. Furthermore, depending on the fuel manufacturing process, artificially introduced dopants (e.g., Co) can provide gamma-ray lines that are usable for burnup monitoring. In fact, it was found that the relative activity of Co-60 to Cs-134 could form an accurate burnup indicator that is independent of power history. In this case, the use of a relative indicator has several advantages, among which is the elimination of the need for absolute knowledge of the detector full energy peak efficiency curve, and the establishment of a system quality assurance figure of merit based on the peak area ratio of the Co lines.

关键词： Monitoring Inductors Fuels Spectroscopy High performance computing Particle measurements Manufacturing processes History Gas detectors Quality assurance

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Direct 3D image reconstruction for the energy subtraction Compton scattering camera (ESCSC) with spatially invariant point spread function

Direct 3D image reconstruction for the energy subtraction Co...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： Junqiang Li J. Valentine Neely Nuclear Research Center Nuclear Radiological Engineering Program of Georgia Institute of Technology Atlanta GA USA

A direct 3D image reconstruction technique has been implemented for the energy subtraction Compton scattering camera (ESCSC) data. By simulating a point source with MCNP and projecting cone surfaces that result from preferred events (defined as photons that undergo a single Compton scattering in the primary detector and then a photoelectric absorption in the secondary detector) into the source space, a point spread function (PSF) describing the characteristics of the imaging system was determined. Based on the Fourier convolution theorem, the PSF was considered as a system response function h(r), and an image was reconstructed via deconvolution using the Fourier transform. For the ESCSC, different weighting schemes can result in spatially invariant or spatially variant PSFs. In this paper, a weighting scheme leading to a nearly spatially invariant PSF was chosen for the backprojection operation. Using MCNP simulated data, several distributed sources were used to test this direct technique. The images of the distributed sources were reconstructed without the existence of simulated noise. Results show that the reconstructed images give reasonable dimensional information of objects, however the intensity recovery is not uniform through the entire object space.

关键词： Image reconstruction Electromagnetic scattering Particle scattering Event detection Detectors Cameras Discrete event simulation Surface reconstruction Absorption Convolution

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A rebinning technique for 3D reconstruction of Compton camera data

A rebinning technique for 3D reconstruction of Compton camer...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： Junqiang Li J.D. Valentine J.N. Aarsvold M. Khamzin Nuclear and Radiological Engineering Program Georgia Institute of Technology Atlanta GA USA Department of Radiology Atlanta GA USA

A newly developed 3D image reconstruction technique for Compton cameras is described. For Compton cameras, the energies and positions of gamma-ray interactions in two detector systems from a single incident photon are recorded using coincidence techniques. Based on this information, the Compton scattering formula establishes a cone surface from which the incident photon must have originated. Instead of projecting the entire cone surface into the image space as is typically done, a number of lines on the cone surface are sampled. All the lines start from the apex of the cone and are evenly distributed over the cone surface. The number of lines on each cone is determined by the desired spatial resolution. A series of imaginary planes are then constructed such that all solid angles (4/spl pi/) that the Compton camera system holds. Each line is then projected to one plane that is mostly perpendicular to this line. The imaginary planes are predefined and grouped into a number of groups with each group having all its planes rotating along one axis. Each group of planes can be treated as the standard SPECT projection data set and one image can be reconstructed using filtered backprojection algorithm. Each group of planes can reconstruct one low statistical image with its specific orientation. Rotating and summing all the images together give the final image.

关键词： Cameras Image reconstruction Single photon emission computed tomography Gamma ray detection Gamma ray detectors Electromagnetic scattering Particle scattering Surface reconstruction Spatial resolution Solids

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Efficiency calculation and coincidence summing correction of a germanium detector by Monte-Carlo simulation

Efficiency calculation and coincidence summing correction of...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： Zhonglu Wang B. Kahn J.D. Valentine Nuclear Radiological Engineering Program of Georgia Institute of Technology Atlanta GA USA Environmental Resources Center Georgia Institute of Technology Atlanta GA USA

A method of efficiency calculation and coincidence-summing correction of a germanium detector by using MCNP code is presented. Modeling of the detector geometry is described in detail and differences between the simulated and measured spectra are discussed. Standard point sources traceable to NIST were used to measure the full-energy peak and total efficiencies. A /sup 60/Co point source was placed in five positions above the detector from 0.6 cm to 14.2 cm. For the 1173 keV and 1332 keV gamma rays from /sup 60/Co, their spectra were simulated by MCNP separately. Subsequently, these spectra were combined according to their coincidence relationship to form the simulated /sup 60/Co spectrum. Cs-137 was used to compare a simple measured spectrum with the MCNP simulation. The simulated full energy peak efficiency for non-coincidence gamma rays agreed with the measured value to within 2%, but the simulated total efficiency is about 8% lower for 662 keV. The calculated coincidence summing factors for 1173 and 1332 keV are about 3% lower than the measured values at the closest geometry for a point source due to the underestimation of the total efficiency. This technique will be used in the efficiency calibration of Ge detectors to avoid the difficulties of preparing standard sources.

关键词： Germanium Gamma ray detection Gamma ray detectors Telephony Monte Carlo methods Computational modeling Geometry Gamma rays Pulse measurements Electronic mail

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MCNP-4c simulations to investigate shielding of scintillation cameras for conjugate imaging of I-123 labeled brain agents

MCNP-4c simulations to investigate shielding of scintillatio...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： D.N. Jangha R.A. Mintzer J.D. Valentine J.N. Aarsvold Nuclear and Radiological Engineering Program Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA USA Division of Nuclear Medicine. Department of Radiology Emory University Atlanta GA USA Nuclear Medicine Service Atlanta Veterans Affairs Medical Center Decatur GA USA

Monte Carlo simulations were performed to characterize various shielding configurations for an iodine-123 (I-123) imaging system. The system comprises two small (10/spl times/10 cm) field-of-view (FOV) gamma cameras to be used for conjugate imaging of I-123 labeled brain agents. 83% of I-123 decays result in 159 keV gamma emissions, which can be readily imaged; while 3% result in emissions with energies from 248 to 783 keV. If the cameras have inadequate shielding, a large amount of activity outside the FOV of the cameras can produce significant image noise due to penetration and scatter of the high energy emissions. A 10 mCi injection of an I-123 labeled neuroreceptor ligand generally results in sub-mCi levels of uptake in the brain-/spl mu/Ci levels of uptake in basal ganglia, while most of any injected dose accumulates in the gastrointestinal (GI) tract. Therefore, sufficient shielding is required if accurate quantification is desired. Various prototype camera designs with wall thicknesses ranging from 1/4 to 3/4 inch were tested via Monte Carlo N-Particle Transport code, version 4c (MCNP-4c) simulation of an idealized primate and a small FOV camera. The primate consisted of water-filled shapes for the head, neck, and trunk. High-energy photons were emitted from a uniform distribution in a spherical GI tract region. The camera consisted of tungsten, lead, and aluminum walls; lead distributed uniformly at 22% density representing a typical high-resolution collimator; photomultiplier tube material; a quartz lightguide; and a 0.8/spl times/10/spl times/10 cm NaI(Tl) scintillation crystal. For each camera configuration, the total energy deposited in the crystal per high-energy source photon was tallied to produce spectra and windowed counts. If a typical high-resolution collimator were to be used in the imaging of a primate head, 10 /spl mu/Ci of focal uptake would result in approximately 12.5 cps in a 159 keV 20% window. For the shielding configurations tested, 10 m

关键词： Brain modeling Cameras Optical imaging Gastrointestinal tract Photonic crystals Testing Head Light scattering Particle scattering Basal ganglia

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Sub- And supercritical bifurcations and turning points in a simple BWR model

Sub- And supercritical bifurcations and turning points in a ...

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2000 ANS International Topical Meeting on Advances in Reactor Physics and Mathematics and Computation into the Next Millennium, PHYSOR 2000

作者： Rizwan-Uddin Department of Nuclear Plasma and Radiological Engineering University of Illinois at Urbana-Champaign UrbanaIL61801 United States Computational Science and Engineering Program University of Illinois at Urbana-Champaign United States

ISBN: (纸本)0894486551

Stability and bifurcation analyses of BWRs have been performed using a reduced order, nuclear-coupled thermal hydraulics model. This has been carried out using a bifurcation analysis code, BIFDD. A large segment of the parameter space has been investigated using this very efficient tool. Stability boundaries are obtained in several two-dimensional parameter spaces. In addition, the nature of bifurcation along these stability boundaries has also been determined. Results indicate that both subcritical as well as supercritical Poincaré-Andronov-Hopf bifurcations are likely to occur in regions of interest in parameter space. In addition to the semi-analytical bifurcation studies, the governing equations have also been integrated numerically. Results confirm the findings of the bifurcation analysis. Numerical integrations, carried out for parameter values away from the stability boundary, further show that the bifurcation curves, in many cases of subcritical bifurcations, have a turning point. The bifurcation curve in these cases extends back into the unstable region. These results show that it is possible to experience large amplitude stable oscillations in the unstable region infinitesimally close to the stability boundary. Moreover, large amplitude stable oscillations are also possible in the stable region of the parameter space near the stability boundary, following large but finite perturbations. These findings provide alternate explanation for the experimental and operational observations in BWRs that indicate the existence of stable limit cycle oscillations and the possibility of growing amplitude oscillations. Results obtained here using a simple model suggest that further work along these lines, with more detailed models, is needed to identify operating conditions and perturbation amplitudes that might lead to stable limit cycles or growing amplitude oscillations in current and next generation of BWRs. © 2000 Proceedings of the PHYSOR 2000 - ANS International To

关键词： Curve fitting

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Nitrogen atom energy distributions in a hollow-cathode planar sputtering magnetron

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Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 2000年第2期61卷 1904-1911页

作者： Wang, Zhehui Cohen, Samuel A. Ruzic, David N. Goeckner, M.J. Los Alamos National Laboratory Los AlamosNM87545 United States Plasma Physics Laboratory Princeton University P.O. Box 451 PrincetonNJ08543 United States Department of Nuclear Plasma and Radiological Engineering University of Illinois UrbanaIL61801 United States Electrical Engineering Program Plasma Science Laboratory University of Texas at Dallas P.O. Box 830688 M/S EC33 DallasTX75083 United States

Energy distributions of nitrogen atoms (N) in a hollow-cathode planar sputtering magnetron were obtained by use of optical emission spectroscopy. A characteristic line, N I 8216.3 A˚, well separated from molecular nitrogen emission bands, was identified. Jansson's nonlinear spectral deconvolution method, refined by minimization of xw2, was used to obtain the optimal deconvolved spectra. These showed nitrogen atom energies from 1 eV to beyond 500 eV. Based on comparisons with VFTRIM computer code results, it is proposed that the energetic N's are generated from N2+ ions after these ions are accelerated through the sheath and dissociatively reflect from the cathode. ©2000 The American Physical Society.

关键词： Cathodes

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A technique for measuring scintillator total electron energy resolution

A technique for measuring scintillator total electron energy...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： W. Mengesha J.D. Valentine Nuclear and Radiological Engineering Program Georgia Institute of Technology Atlanta GA USA

A technique for determining the total electron energy resolution (/spl eta//sub e,tot/) of scintillators is described. The technique is based on measurement of the full-width at half maximum of the scintillator coincidence energy spectrum using the previously developed Compton coincidence technique (CCT). For determining /spl eta//sub e,tot/, the CCT was modified to accommodate variable collimation of the scattered photons. MCNP simulations were used to guide development of data analysis techniques. Preliminary measurements indicate /spl eta//sub e,tot/ variation as the inverse square root of the electron energy over a limited energy range.

关键词： Energy measurement Electrons Energy resolution Detectors Collimators Geometry Solids Current measurement Pulse measurements Scattering

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Improved radioxenon detection techniques for use with fluid-based concentration

Improved radioxenon detection techniques for use with fluid-...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： W.R. Russ D.O. Stuenkel J.D. Valentine K.C. Gross Georgia Institute of Technology Nuclear and Radiological Engineering Program Atlanta GA USA Nuclear and Radiological Engineering Program University of Cincinnati Cincinnati OH USA Reactor Analysis Division Argonne National Laboratory Argonne IL USA

A portable system that monitors the quantity of radioxenon (/sup 131m/Xe, /sup 133/Xe, /sup 133m/Xe, and /sup 135/Xe) in the atmosphere is being developed. The integrated monitoring system consists of a fluid-based concentration sub-system and a detection subsystem. This study evaluates the performance of different high-efficiency geometries that use NaI(Tl) photon detectors along with with either gas proportional, plastic scintillator, or PIPS detectors to distinguish radioxenon signature emissions and discriminate against radon background. In addition, a NaI(Tl)/CsI(Tl) phoswich detector was investigated as an alternative photon detector. Finally, a dual parameter data acquisition system was demonstrated. Minimum detectable activity (MDA) for a six hour count time was used as the primary measure of performance. The lowest MDAs were 52/spl plusmn/7 mBq for the gas proportional/NaI(Tl) configuration, 48/spl plusmn/7 mBq for the plastic scintillator/NaI(Tl) configuration and 73/spl plusmn/8 mBq for the PIPS/NaI(Tl) configuration. Based on these results, the performance of a proposed final detection system is predicted to result in a MDA of 22.2 mBq without shielding. This detection system performance compares well to existing radioxenon detection systems and indicates the requirements of the concentration system.

关键词： Detectors Event detection Plastics Electrons Geometry Monitoring Data acquisition System performance Xenon Isotopes

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Fault-tolerance improvement for a MSET model of the Crystal River-3 feedwater flow system

Fault-tolerance improvement for a MSET model of the Crystal ...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： A. Miron S. Wegerich F. Yue K. Gross J. Christenson Nuclear and Radiological Engineering Program University of Cincinnati Cincinnati OH USA Reactor Analysis Division Argonne National Laboratory Argonne IL USA

In this paper we expand on the results reported previously to include an effective method for improving the fault tolerance of an empirical PWR feedwater flow system model.

关键词： Fault tolerant systems State estimation Inductors Signal processing Fault detection Sensor systems Laboratories Fluid flow measurement Calibration Data mining

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