222 research outputs found
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Advanced Materials and Processes for High Energy Resolution Room Temperature Gamma Ray Spectrometers
A significant amount of progress has been achieved in the development of the novel vacuum distillation method described in the proposal. The process for the purification of Te was fully developed and characterized in a series of trials. The purification effect was confirmed with GDMS sample analysis and indicates the process yields very high purity Te metal. Results of this initial process study have been submitted for publication in the Proceedings of the SPIE and will be presented on August 28, 2007 at the SPIE Optics and Photonics 2007 conference in San Diego, CA. Concurrent to the development of the Te process, processes for the purification of Cd, Zn, and Mn have also progressed. The development of the processes for Cd and Zn are nearly complete, while the development of the process for Mn is still in its infancy. It is expected that a full characterization of the Cd process will be completed within the next quarter, followed by Zn. Parallel to those characterization studies, efforts will be made to further develop the Mn purification process. Zone melting work for Te and Cd has also been efforted as per the project work schedule. Initial trials have been completed and the processes developed. Characterization of the results will be completed within the first fiscal year. Finally, an apparatus for the zone refinement of Cd, Zn, and Mn has been constructed and initial trials are set to begin shortly
Numerical Evaluation of Micro-Pocket Fission Detectors
Micro-pocket fission detectors (MPFDs) are miniature fission chambers suitable for in-core neutron measurement that have been under development at Kansas State University for over one decade. Current-generation devices have been used at a number of university reactors (Kansas State, Wisconsin, and MIT) and as part of the first experiments performed during the recent restart of TREAT. Ongoing research aims to improve understanding of the existing MPFDs and to optimize designs for future deployment. To aid in this development, the dynamic response of a prototypic MPFD was evaluated using Garfield++, Elmer, Gmsh, and Stopping and Range of Ions in Matter (SRIM). Specifically, the finite-element code Elmer was used to calculate the electric field on a mesh generated by Gmsh. SRIM was used to compute the energy loss tables of the fission fragments in the gas. With output from Elmer and SRIM, Garfield++ was used to simulate the ionization process, the resulting electron drift, and the induced signal. This particular Garfield++ application was developed with hybrid parallelization based MPI and OpenMP. The performance of the MPFDs subjected to different temperatures and applied voltages was evaluated. The preliminary results indicate the fission fragment deposits a few MeV of energy in the gas, consistent with previous estimates. The pulses in the MPFDs can be formed in the nanosecond scale, thus accommodating high count rates and, hence, high neutron-flux levels. Ongoing work aims to extend this model and validate it against existing and planned experimental data
Development of semiconductor detectors for fast neutron radiography
A high-energy neutron detector has been developed using a semiconductor diode fabricated from bulk gallium arsenide wafers with a polyethylene neutron converter layer. Typical thickness of the diode layer is 250 to 300 μm with bias voltages of 30 to 150 volts. Converter thicknesses up to 2030 μm have been tested. GaAs neutron detectors offer many advantages over existing detectors including positional information, directional dependence, gamma discrimination, radiation hardness, and spectral tailoring. Polyethylene-coated detectors have been shown to detect 14 MeV neutrons directly from a D-T neutron generator without interference from gamma rays or scattered neutrons. An array of small diode detectors can be assembled to perform fast neutron radiography with direct digital readout and real-time display of the image produced. In addition, because the detectors are insensitive to gamma rays and low energy neutrons, highly radioactive samples (such as spent nuclear fuel or transuranic waste drums) could be radiographed. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87673/2/1118_1.pd
Erratum: ‘‘Evidence for field enhanced electron capture by EL2 centers in semi‐insulating GaAs and the effect on GaAs radiation detectors’’ [J. Appl. Phys. 75, 7910 (1994)]
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69985/2/JAPIAU-77-3-1331-1.pd
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Near-Core and In-Core Neutron Radiation Monitors for Real Time Neutron Flux Monitoring and Reactor Power Level Measurements
MPFDs are a new class of detectors that utilize properties from existing radiation detector designs. A majority of these characteristics come from fission chamber designs. These include radiation hardness, gamma-ray background insensitivity, and large signal output
Evidence for field enhanced electron capture by EL2 centers in semi‐insulating GaAs and the effect on GaAs radiation detectors
The performance of Schottky contact semiconductor radiation detectors fabricated from semi‐insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi‐insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi‐insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71231/2/JAPIAU-75-12-7910-1.pd
First Steps Towards an Understanding of a Mode ofCarcinogenic Action for Vanadium Pentoxide
Inhalation of vanadium pentoxide clearly increases the incidence of
alveolar/bronchiolar neoplasms in male and female B6C3F1 mice at all
concentrations tested (1, 2 or 4 mg/m3), whereas responses in F344/N
rats was, at most, ambiguous. While vanadium pentoxide is mutagenic in
vitro and possibly in vivo in mice, this does not
explain the species or site specificity of the neoplastic response. A nose-only
inhalation study was conducted in female B6C3F1 mice (0, 0.25, 1 and
4 mg/m3, 6 h/day for 16 days) to explore histopathological,
biochemical (α-tocopherol, glutathione and F2-isoprostane) and genetic (comet
assays and 9 specific DNA-oxo-adducts) changes in the lungs. No treatment
related histopathology was observed at 0.25 mg/m3. At 1 and
4 mg/m3, exposure-dependent increases were observed in lung
weight, alveolar histiocytosis, sub-acute alveolitis and/or granulocytic
infiltration and a generally time-dependent increased cell proliferation rate of
histiocytes. Glutathione was slightly increased, whereas there were no
consistent changes in α-tocopherol or 8-isoprostane F2α. There was no evidence
for DNA strand breakage in lung or BAL cells, but there was an increase in
8-oxodGuo DNA lesions that could have been due to vanadium pentoxide induction
of the lesions or inhibition of repair of spontaneous lesions. Thus, earlier
reports of histopathological changes in the lungs after inhalation of vanadium
pentoxide were confirmed, but no evidence has yet emerged for a genotoxic mode
of action. Evidence is weak for oxidative stress playing any role in lung
carcinogenesis at the lowest effective concentrations of vanadium pentoxide
Evidence for field enhanced electron capture by EL2 centers in semi-insulating GaAs and the effect on GaAs radiation detectors
The performance of Schottky contact semiconductor radiation detectors fabricated from semi-insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi-insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi-insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements
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