37 research outputs found
Radioactivities induced in some LDEF samples
Radioactivities induced in several Long Duration Exposure Facilities (LDEF) samples were measured by low-level counting at Los Alamos and elsewhere. These radionuclides have activities similar to those observed in meteorites and lunar samples. Some trends were observed in these measurements in terms of profiles in trunnion layers and as a function of radionuclide half-life. Several existing computer codes were used to model the production by the protons trapped in the Earth's radiation belts and by the galactic cosmic rays of some of these radionuclides, Mn-54 and Co-57 in steel, Sc-46 in titanium, and Na-22 in alloys of titanium and aluminum. Production rates were also calculated for radionuclides possibly implanted in LDEF, Be-7, Be-10, and C-14. Enhanced concentrations of induced isotopes in the surfaces of trunnion sections relative to their concentrations in the center are caused by the lower-energy protons in the trapped radiation. Secondary neutrons made by high-energy trapped protons and by galactic cosmic rays produce much of the observed radioactivities, especially deep in an object. Comparisons of the observed to calculated activities of several radionuclides with different half-lives indicate that the flux of trapped protons at LDEF decreased significantly at the end of the mission
Press Conference - Washington, D.C. - Senator Frank E. Moss and Governor Calvin L. Rampton Endorse Senator Edmund S. Muskie as Democratic Presidential Candidate
Senator Frank E. Moss and Governor Calvin L. Rampton endorse Senator Edmund S. Muskie as the Democratic Presidential candidate during a press conference in Washington, D.C
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High-precision gamma-ray total cross-section measurements between 3.45 and 12 MeV
A Compton-backscatter capability has recently become available at the Duke University Free Electron Laser Laboratory. This capability allows one to produce high fluxes of tunable, nearly monoenergetic gamma rays. Using these gamma-ray beams, we have made high-precision (~0.5%) measurements of the gamma-ray total cross section at 3.45, 4, 5, 6, 8, 10, and 12 MeV. The nuclei measured were Be, C, Cu, Ta, W, Pb, and
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Measurement of gamma-ray total absorption cross sections using a [sup 56]Co source
We have used a 150 MBq [sup 56]Co source to perform gamma-ray total absorption cross section measurements with very high precision. The use of [sup 56]Co allowed us to simultaneously measure the total cross section at 15 energies ranging from 0.847 MeV to 3.451 MeV. Seven sample materials were measured: Be, C, Cu, Ta, W, Pb, and U. In general, the measurement precision is better than 0.5% and in all cases better than 1.3%
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CdZnTe gamma ray spectrometer for orbital planetary missions
Knowledge of surface elemental composition is needed to understand the formation and evolution of planetary bodies. Gamma rays and neutrons produced by the interaction of galactic cosmic rays with surface materials can be detected from orbit and analyzed to determine composition. Using gamma ray spectroscopy, major rock forming elements such as Fe, Ti, Al, Si, Mg, and Ca can be detected. The accuracy of elemental abundance is limited by the resolution of the spectrometer. For space missions, scintillators such as BGO and NaI(Tl) have been used for gamma ray spectroscopy. New planetary science missions are being planned to explore Mars, Mercury, the asteroid belt, and the outer planets. Significant improvements in the pulse height resolution relative to scintillation detectors can be made using CdZnTe, a new room temperature detector technology. For an orbiting instrument, a CdZnTe detector at least 16 cm{sup 3} in size is needed. A 4 x 4 array of 1-cm{sup 3} coplanar grid detectors can be manufactured that meets requirements for resolution and counting efficiency. The array will shielded from gamma rays produced in the spacecraft by a BGO detector. By improving pulse height resolution by a factor of three at low energy, the CdZnTe detector will be able to make accurate measurements of elements that are currently difficult to measure using scintillation technology. The BGO shield will provide adequate suppression of gamma rays originating in the spacecraft, enabling the gamma ray spectrometer to be mounted on the deck of a spacecraft. To test this concept, we are constructing a flight qualified, prototype CdZnTe detector array. The prototype consists of a 2 x 2 array of coplanar grid detectors. We will present the results of mechanical and electronic testing and radiation damage tests, and the performance of the array for gamma ray spectroscopy
Selection of climate policies under the uncertainties in the Fifth Assessment Report of the IPCC
Analysis of uncertainty decision making criteria
Title: High-energy characterization of two large-volume multi-element CdZnTe detectors High-energy characterization of two large-volume multi-element CdZnTe detectors
ABSTRACT We present results of experiments to characterize two large-volume, multi-element CdZnTe detectors for gamma-ray spectroscopy at high energy. The first detector consisted of four 1.5 cm ´ 1.5 cm ´ 0.75 cm coplanar grid detectors. The measurements for the four-element design were performed with various configurations. The second detector consisted of eight 1 cm ´ 1 cm ´ 0.5 cm coplanar grid detectors arranged in a 2 ´ 2 ´ 2 array. The high-energy gamma-ray sources included 60 Co(1332), 228 T