Prettyman T.H.,Planetary Science Institute |
Feldman W.C.,Planetary Science Institute |
McSween Jr. H.Y.,University of Tennessee at Knoxville |
Dingler R.D.,Los Alamos National Laboratory |
And 7 more authors.
Space Science Reviews
The NASA Dawn Mission will determine the surface composition of 4 Vesta and 1 Ceres, providing constraints on their formation and thermal evolution. The payload includes a Gamma Ray and Neutron Detector (GRaND), which will map the surface elemental composition at regional spatial scales. Target elements include the constituents of silicate and oxide minerals, ices, and the products of volcanic exhalation and aqueous alteration. At Vesta, GRaND will map the mixing ratio of end-members of the howardite, diogenite, and eucrite (HED) meteorites, determine relative proportions of plagioclase and mafic minerals, and search for compositions not well sampled by the meteorite collection. The large south polar impact basin may provide an opportunity to determine the composition of Vesta's mantle and lower crust. At Ceres, GRaND will provide chemical information needed to test different models of Ceres' origin and thermal and aqueous evolution. GRaND is also sensitive to hydrogen layering and can determine the equivalent H 2O/OH content of near-surface hydrous minerals as well as the depth and water abundance of an ice table, which may provide information about the state of water in the interior of Ceres. Here, we document the design and performance of GRaND with sufficient detail to interpret flight data archived in the Planetary Data System, including two new sensor designs: an array of CdZnTe semiconductors for gamma ray spectroscopy, and a loaded-plastic phosphor sandwich for neutron spectroscopy. An overview of operations and a description of data acquired from launch up to Vesta approach is provided, including annealing of the CdZnTe sensors to remove radiation damage accrued during cruise. The instrument is calibrated using data acquired on the ground and in flight during a close flyby of Mars. Results of Mars flyby show that GRaND has ample sensitivity to meet science objectives at Vesta and Ceres. Strategies for data analysis are described and prospective results for Vesta are presented for different operational scenarios and compositional models. © Springer Science+Business Media B.V. 2011. Source
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.55K | Year: 2006
The non-scaling Fixed Focus Alternating Gradient (FFAG) Accelerator is of strong interest for DOE facilities and commercial applications as a less expensive, faster cycling, and more-readily-operable device. This project will investigate the feasibility of this concept and plan for the construction of a scaled electron prototype. Phase I will develop an optimum lattice design, which will be scaled to given high-energy applications and based on a beam dynamic assessment that uses analytical and particle tracking. A first-order magnet design, suitable to the electron prototype, will be developed. In Phase II, the magnet design will be refined, tested against performance in the lattice (beam dynamics, field errors, alignability, etc.), and a lattice cell will be constructed. The results should lead to eventual construction of the electron prototype in Phase III. Commercial Applications And Other Benefits as described by the Applicant: A simple economical accelerator should provide substantial benefits to the DOE in terms of the costs of constructing new accelerators and upgrading existing ones. Examples include an AGS beam-power upgrade, high-intensity proton drivers for nuclear physics, waste transmutation, radioisotope production, and high-intensity sychrotron radiation. In addition, the accelerator should have application to ion implantation, sterilization, and medical proton therapy
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 0.00 | Year: 2002
65480 The production of intense fission product radioactive beams used for nuclear physics research requires special target approaches. One such approach is that of a two-step target, in which an energetic, intense light-ion beam strikes a cooled heavy metal target to create neutrons, and the neutrons cause fissions in a surrounding blanket to make the fission products. However, such a target has not been demonstrated to work using an intense production of light ions. This project will construct a prototype two-step target and demonstrate the efficacy of the concept. Phase I produced a numerical analysis of a two-step target, defining the dimensions and constituents of a prototype target. The analysis included estimates of neutron production, fission rates, and energy deposition in the primary and secondary targets. This was followed by a thermal analysis using finite element approaches to devise cooling strategies for the primary target and thermal control approaches for the secondary target. Phase II will demonstrate the efficacy of a prototype two-step target using an intense production beam. The analyses of the thermal performances of the target components from the Phase I study will be extended, and a prototype test target will be designed in detail, fabricated, and integrated into a test configuration at the TRIUMF accelerator. Commercial Applications and Other Benefits as described by the awardee: This technology should lead to the commercial provision of targets for intense radioactive beam facilities, including the new nuclear physics initiative, the Rare Isotope Accelerator.
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.16K | Year: 2004
75153-Electron cloud effects are a critical technical risk for the next generation of high intensity proton and positron rings, to be used in facilities for High Energy Physics research. New diagnostics are required to observe electron cloud formation and trapping and to test theories and simulations of various beam dynamics issues. In particular, no such diagnostics have been developed for use in quadrupole magnets, where electron trapping is expected to play a large role. This project will undertake an analysis of the electron sweeping detector concept, in order to develop an optimized physics design for an electron cloud diagnostic for use in quadrupole magnets at high intensity proton or positron rings. In Phase I, a concept for an electron sweeping diagnostic for use in quadrupole magnets will be developed, various electron trajectories will be calculated, the physics design will be optimized, and engineering feasibility will be determined. In Phase II, a prototype will be engineered, fabricated and tested, and initial experimental data will be gathered at an existing facility, such as the Los Alamos Proton Storage Ring. Commercial Applications and Other Benefits as described by the awardee: The results of this project should directly benefit the high intensity proton and positron rings under construction or under active consideration. These include the Spallation Neutron Source, the Next Linear Collider, and Neutrino Factories.
Hardgrove C.,University of Tennessee at Knoxville |
Moersch J.,TechSource, Inc. |
Drake D.,TechSource, Inc.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
The Dynamic Albedo of Neutrons (DAN) experiment, part of the scientific payload of the Mars Science Laboratory (MSL) rover mission, will have the ability to assess both the abundance and the burial depth of subsurface hydrogen as the rover traverses the Martian surface. DAN will employ a method of measuring neutron fluxes called neutron die-away that has not been used in previous planetary exploration missions. This method requires the use of a pulsed neutron generator that supplements neutrons produced via spallation in the subsurface by the cosmic ray background. It is well established in neutron remote sensing that low-energy (thermal) neutrons are sensitive not only to hydrogen content, but also to the macroscopic absorption cross-section of near-surface materials. To better understand the results that will be forthcoming from DAN, we model the effects of varying abundances of high absorption cross-section elements that are likely to be found on the Martian surface (Cl, Fe) on neutron die-away measurements made from a rover platform. Previously, the Mars Exploration Rovers (MER) Spirit and Opportunity found that elevated abundances of these two elements are commonly associated with locales that have experienced some form of aqueous activity in the past, even though hydrogen-rich materials are not necessarily still present. By modeling a suite of H and Cl compositions, we demonstrate that (for abundance ranges reasonable for Mars) both the elements will significantly affect DAN thermal neutron count rates. Additionally, we show that the timing of thermal neutron arrivals at the detector can be used together with the thermal neutron count rates to independently determine the abundances of hydrogen and high neutron absorption cross-section elements (the most important being Cl). Epithermal neutron die-away curves may also be used to separate these two components. We model neutron scattering in actual Martian compositions that were determined by the MER Alpha Proton X-Ray Spectrometer (APXS), as examples of local geochemical anomalies that DAN would be sensitive to if they were present at the MSL landing site. These MER targets, named Eileen Dean, Jack Russell, and Kenosha Comets, all have unusually high or low Cl or Fe abundances as a result of geochemical interactions involving water. Using these examples we demonstrate that DAN can be used not only to assess the amount of present-day hydrogen in the near-surface but also to identify locations that may preserve a geochemical record of past aqueous processes. © 2011 Elsevier B.V. All rights reserved. Source