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IEEE Symposium on nuclear science (NSS/MIC)

作者： Soo-Jin Lee Mi No Lee Van-Giang Nguyen Soo Mee Kim Jae Sung Lee Department of Electronic Engineering Pai Chai University Daejeon South Korea Department of Nuclear Medicine and Interdisciplinary Program in Radiation Applied Life Science Seoul National University Seoul South Korea

Compton imaging is often recognized as a potentially more valuable 3-D technique than conventional emission tomography. However, due to the inherent complexity of massive data set computations for the conical projection-backprojection operation, most reconstruction algorithms have been based on analytical methods rather than statistical methods. In this paper, we investigate a maximum a posteriori (MAP) approach to Compton camera reconstruction, which provides reconstructions with superior noise characteristics compared to analytical methods. In order to preserve edges that can occur occasionally in the underlying object, we use a convex-nonquadratic smoothing prior and apply to a row-action based regularized maximum likelihood method, which is provably convergent to a true MAP solution. Our preliminary results indicate that, although the statistical methods considered in this paper are not as fast as analytical methods, they have a great potential to improve quantitative accuracy in Compton imaging.

关键词： Cameras Image reconstruction Electromagnetic scattering Particle scattering Telephony Event detection Power engineering and energy Acceleration Reconstruction algorithms Statistical analysis

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Flux-limited diffusion coefficients in reactor physics applications

Flux-limited diffusion coefficients in reactor physics appli...

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Joint International Topical Meeting on Mathematics and Computations and Supercomputing in nuclear Applications, M and C + SNA 2007

作者： Pounders, Justin Rahnema, Farzad Szilard, Ronaldo Nuclear and Radiological Engineering/Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA 30332-0405 Idaho National Laboratory Nuclear Programs Nuclear Science and Engineering Division Idaho Falls ID 83415

ISBN: (纸本)0894480596

Flux-limited diffusion theory has been successfully applied to problems in radiative transfer and radiation hydrodynamics, but its relevance to reactor physics has not yet been explored. The current investigation compares the performance of a flux-limited diffusion coefficient against the traditionally defined transport cross section. A one-dimensional BWR benchmark problem is examined at both the assembly and full-core level with varying degrees of heterogeneity.

关键词： Boiling water reactors

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Mechanisms of scent-tracking in humans (vol 10, pg 27, 2007)

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NATURE NEUROscience 2007年第2期10卷 263-263页

作者： Porter, Jess Craven, Brent Khan, Rehan M. Chang, Shao-Ju Kang, Irene Judkewitz, Benjamin Volpe, Jason Settles, Gary Sobel, Noam 299 Life Science Addition MC 3200 Program in Biophysics University of California Berkeley Berkeley California 94720 USA. Department of Mechanical and Nuclear Engineering Penn State University University Park Pennsylvania 16802 USA. Department of Psychology University of California Berkeley Berkeley California 94720 USA. Program in Bioengineering University of California Berkeley Berkeley California 94720 USA. Program in Bioengineering University of California Berkeley Berkeley California 94720 USA. Helen Wills Neuroscience Institute University of California Berkeley Berkeley California 94720 USA. Department of Mechanical and Nuclear Engineering Penn State University University Park Pennsylvania 16802 USA. Department of Mechanical and Nuclear Engineering Penn State University University Park Pennsylvania 16802 USA. Department of Neurobiology The Weizmann Institute of Science Rehovot Israel.

Whether mammalian scent-tracking is aided by inter-nostril comparisons isunknown. We assessed this in humans and found that (i) humans can scent-track, (ii) they improvewith practice, (iii) the human nostrils sample spatially distinct regions separated by approximately3.5 cm and, critically, (iv) scent-tracking is aided by inter-nostril comparisons. These findingsreveal fundamental mechanisms of scent-tracking and suggest that the poor reputation of humanolfaction may reflect, in part, behavioral demands rather than ultimate abilities.

关键词： Learning Odors Recognition (Psychology) Smell

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Moderator neutron pulse-shape study for the NxGENS long-pulse spallation source

Moderator neutron pulse-shape study for the NxGENS long-puls...

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8th International Topical Meeting on nuclear Applications and Utilization of Accelerators, ACCAPP'07

作者： Willis, Carl Muhrer, Guenter Nuclear Engineering Program The Ohio State University 201 W. 19th Ave. Columbus OH 43210 United States Los Alamos Neutron Science Center MS H813 Los Alamos NM 87545 United States

ISBN: (纸本)0894480545

We present results of MCNPX modeling of the neutron pulse time structure delivered by moderators under investigation for the proposed NxGENS long-pulse spoliation neutron source at the Los Alamos Neutron science Center. As envisioned at the time of this work, low-energy neutrons would be produced for the NxGENS flight path by a single "backscattering" moderator of either water or liquid hydrogen in proximity to a tungsten-reflected tungsten target bombarded by 800 MeV protons. Specifically, our results here pertain to a 9.2 cm thick water moderator, and a 5.2 cm thick liquid hydrogen moderator with ortho:para ratio of 1:1. It was found that the Ikeda-Carpenter model accurately represents the storage of neutrons in these moderators, but that there are inaccuracies in the time region dominated by slowingdown. We suspect that inhomogeneity of the moderators, their limited size, and neutronic coupling of the moderators to their surroundings may be responsible for the observed disparities with this model.

关键词： Moderators

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Novel Preparation Methods for the Fabrication of Thin‐Film EXAFS Samples

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AIP Conference Proceedings 2007年第1期882卷 908-910页

作者： M. C. Ridgway C. J. Glover P. Kluth B. Johannessen G. J. Foran 1Department of Electronic Materials Engineering Australian National University Canberra Australia 2Australian Synchrotron Research Program Australian Nuclear Science and Technology Organisation Menai Australia

Thin‐film EXAFS samples have been fabricated using semiconductor‐processing and wet‐chemical etching techniques to eliminate artifacts associated with transmission and fluorescence measurements. Examples include crystalline GexSi1−x alloys, amorphous GaAs and Cu and Au nanocrystals in SiO2. In general, thin films of several microns thickness were first formed on bulk substrates then EXAFS samples were fabricated by separating the thin film and substrate. For transmission measurements, thin films were stacked together to yield the optimum absorption while sample inhomogeneity, non‐uniformity and non‐continuity were readily eliminated. For fluorescence measurements, scattering/diffraction from the substrate was eliminated and stacking the thin films together increased the areal concentration of the absorber. The use of such techniques to fabricate EXAFS samples yielded a significant increase in accessible photo‐electron wave number range and hence more accurate structural parameter determinations.

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A Novel Method Improving the Imaging Resolution of a Table-top Compton Camera

A Novel Method Improving the Imaging Resolution of a Table-t...

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2007 IEEE nuclear science Symposium Conference (NSS 2007), vol.7

作者： Hee Seo Se Hyung Lee Jong Hwi Jeong Ju Hahn Lee Chun Sik Lee Jae Sung Lee Chan Hyeong Kim Department of Nuclear Engineering Hanyang University Seoul South Korea Department of Physics Chung-Ang University Seoul South Korea Department of Nuclear Medicine and Interdisciplinary Program in Radiation Applied Life Science Seoul National University Seoul South Korea

For a table-top Compton camera, which is currently under development in our group, the interaction position resolution of the absorber detector is a critical or limiting detector parameter that most seriously affects the imaging resolution of the Compton camera. Currently, it is assumed that all the interactions occur at the centers of the detector segments of the absorber detector, which is simple, but obviously not the best choice considering that the interaction depths of the photons in the absorber detector is not distributed uniformly, especially for the low-energy photons. To this end, the present study develops a novel method, called "average interaction depth (AID) method" to improve the imaging resolution of Compton camera by additionally considering the interaction depth of the incident photon in the absorber detector. Our simulation studies with Geant4 show that the imaging resolution of Compton camera can be significantly improved by using the AID method. The imaging resolution of the table-top Compton camera was improved from 9.9mm to 7.6mm in full width at half maximum (FWHM) for a 511keV γ point source. For a 364keV γ point source, the imaging resolution was improved more significantly, i.e., from 11.4mm to 7.2mm.

关键词： Image resolution Cameras

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Fully three-dimensional image reconstruction for compton imaging using ordered subsets of conical projection data

Fully three-dimensional image reconstruction for compton ima...

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IEEE Symposium on nuclear science (NSS/MIC)

作者： Soo Mee Kim Jae Sung Lee Soo-Jin Lee Department of Nuclear Medicine and Interdisciplinary Program in Radiation Applied Life Science College of Medicine and Institute of Radiation Medicine Medical Research Center Seoul National University South Korea Electronic Engineering Department Pai Chai University Daejeon South Korea

The Compton camera has recently been recognized as a promising three-dimensional imaging modality with higher sensitivity and unlimited field-of-view. Due to computational limitations, however, it has been of a difficult problem to develop reconstruction algorithms with good. In this study, we propose efficient methods for implementing the OSEM (ordered-subsets expectation-maximization) algorithm for Compton camera reconstruction, and investigate three different schemes for grouping Compton scattered data into ordered subsets. The first is to group the data according to a pre-set order of scattering angles, the second is to group the possible combinations of detected position pairs in the scatterer and the absorber, and the third is to combine the first and second methods. According to our experimental results, all of the three grouping schemes exhibit similar performance in terms of the quantitative accuracy and computational efficiency. Our results show that the OSEM algorithm applied to the Compton camera provides an order improvement in speed of execution while retaining overall quality of the image reconstructed by the standard EM algorithm.

关键词： Image reconstruction Electromagnetic scattering Particle scattering Cameras Biomedical imaging Event detection Reconstruction algorithms Position sensitive particle detectors Telephony Collimators

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TRIM modeling of displacement damage in SiC for monoenergetic neutrons

Journal of ASTM International

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Journal of ASTM International 2006年第8期3卷

作者： Khorsandi, B. Blue, T.E. Windl, W. Kulisek, J. Ohio State University Nuclear Engineering Program Columbus OH 43202 Ohio State University Department of Materials Science and Engineering Columbus OH 43210

Although silicon carbide is a very good semiconductor material for the fabrication of diode detectors for use as neutron power monitors in nuclear reactors, the electrical properties of the diodes may be altered because of interactions between energetic neutrons and SIC atoms. If the energy that is transferred from a neutron to an atom in a collision exceeds some threshold value, the atom will be moved from its original position, creating displacement damage. Accurately modeling displacement damage is a first step to finding ways to eliminate or decrease the amount of damage the displacements induce. The methodology that we have used to estimate the number of displacements per atom per fluence, using two codes (MCNP and TRIM) is presented in this paper, along with examples of the results of our calculations. Copyright © 2006 by ASTM International.

关键词： Silicon carbide

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The 2+2 scholars program: Collaborative undergraduate nuclear engineering education in Idaho

The 2+2 scholars program: Collaborative undergraduate nuclea...

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113th Annual ASEE Conference and Exposition, 2006

作者： Dunzik-Gougar, Mary Lou Lineberry, Michael Bond, Leonard Idaho State University United States Institute of Nuclear Science and Engineering ISU United States 2+2 Nuclear Engineering Scholarship Program Institute of Nuclear Science and Engineering Idaho State University University of Idaho United States Department of Nuclear Engineering ISU Idaho National Laboratory United States Center for Advanced Energy Studies Idaho National Laboratory United States

The 2 + 2 Scholars program brings together nuclear engineering undergraduate students from three Idaho universities - Idaho State University (ISU), the University of Idaho (UI), and Boise State University (BSU) - to spend their junior and senior years in Idaho Falls, attending classes at University Place (a joint campus of ISU and UI) while working as interns at the Department of Energy's Idaho National Laboratory (INL) and using INL facilities for coursework. Scholarship funds are provided by the AREVA Group and the DOE. © American Society for engineering Education, 2006.

关键词： nuclear engineering

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Incorporation of Markov reliability models for digital instrumentation and control systems into existing PRAs

Incorporation of Markov reliability models for digital instr...

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5th International Topical Meeting on nuclear Plant Instrumentation Controls, and Human Machine Interface Technology (NPIC and HMIT 2006)

作者： Bucci, P. Mangan, L.A. Kirschenbaum, J. Mandelli, D. Aldemir, T. Arndt, S.A. Ohio State University Dept. of Computer Science and Engineering 395 Dreese Labs. 2015 Neil Ave. Columbus OH 43210 Ohio State University Nuclear Engineering Program 650 Ackerman Road Columbus OH 43202 U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research Washington DC 20555

ISBN: (纸本)0894480510

Markov models have the ability to capture the statistical dependence between failure events that can arise in the presence of complex dynamic interactions between components of digital instrumentation and control systems. One obstacle to the use of such models in an existing probabilistic risk assessment (PRA) is that most of the currently available PRA software is based on the static event-tree/fault-tree methodology which often cannot represent such interactions. We present an approach to the integration of Markov reliability models into existing PRAs by describing the Markov model of a digital steam generator feedwater level control system, how dynamic event trees (DETs) can be generated from the model, and how the DETs can be incorporated into an existing PRA with the SAPHIRE software.

关键词： nuclear instrumentation

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