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Effects of an RTG power source on neutron spectroscopy measurements on the martian surface.

Description: A continuing goal of Mars science is to identify the exact locations of near-surface water and/or hydrated minerals using in situ measurements. Recent data from the Mars Odyssey mission has used both neutron and gamma-ray spectroscopy to measure large amounts of water ice near both polar regions . Furthermore, these data have also determined that in the mid-latitude regions, there likely exist relatively large amounts of hydrogen (-4-7 equivalent H2O wt.%), although it is not certain in which form this hydrogen exists . While these are exciting results, one drawback of these measurements is that they are averaged over a large (-400 km) footp ri nt and do not reflect any small (<1 km) inhomogenieties in hydrogen abundance that likely exist on the Martian surface. For any future in situ mission (e g, Mars Smart Lander (MSL)) that seeks to measure and characterize nearsurface H 2O, especially in the mid-latitude regions, is will be necessary to know th e locati ons of the H20.
Date: January 1, 2003
Creator: Lawrence, David J. (David Jeffery),; Elphic, R. C. (Richard C.) & Wiens, R. C. (Roger C.)
Partner: UNT Libraries Government Documents Department

Development of an ultracompact neutron spectrometer for identifying near-surface water on mars.

Description: One of the major goals of the Mars science program is to identify exact locations of near-surface water or hydrated minerals on Mars. Evidence is mounting that Mars may have contemporary near-surface groundwater activity. Though very water-poor by terrestrial igneous standards, the SNC meteorivtes were found to contain evaporite minerals suggestive of groundwater activity within the past 1.3 Ga. More recently, the Mars Surveyor camera recorded images of geologically young seepage and outflow channels attributed to liquid water. The sources of these channels were suggested to be only a few hundred meters or less below the surface. If these channels are truly geologically young, thinly buried ice may still exist at the termination of these channels.
Date: January 1, 2001
Creator: Lawrence, David J. (David Jeffery); Wiens, R. C. (Roger C.); Moore, K. R. (Kurt R.) & Prettyman, T. H. (Thomas H.)
Partner: UNT Libraries Government Documents Department

In situ neutron spectroscopy on the martian surface: modeling the hydra instrument for different mission scenarios

Description: Neutron spectroscopy has proven to be highly successful in remotely detecting and measuring the abundance of water on planetary surfaces such as Mars and the Moon. Because of the central role played by water on Mars and the need to make in situ measurements of water abundances for landed missions, neutron spectroscopy is being investigated as a technique for quickly determining the near-surface water abundance for fhture Mars missions, such as the Mars Smart Larider (MSL).
Date: January 1, 2003
Creator: Lawrence, David J. (David Jeffery),; Elphic, R. C. (Richard C.); Feldman, W. C. (William C.); Moore, K. R. (Kurt R.); Prettyman, T. H. (Thomas H.) & Weins, R. C. (Roger C.)
Partner: UNT Libraries Government Documents Department

Lunar surface outgassing and alpha particle measurements

Description: The Lunar Prospector Alpha Particle Spectrometer (LP APS) searched for lunar surface gas release events and mapped their distribution by detecting alpha particle?; produced by the decay of gaseous radon-222 (5.5 MeV, 3.8 day half-life), solid polonium-2 18 (6.0 MeV, 3 minute half-life), and solid polonium-210 (5.3 MeV, 138 day half-life, but held up in production by the 21 year half-life of lead-210). These three nuclides are radioactive daughters from the decay of uranium-238.
Date: January 1, 2002
Creator: Lawson, S. L. (Stefanie L.); Feldman, W. C. (William C.); Lawrence, David J. (David Jeffery),; Moore, K. R. (Kurt R.); Elphic, R. C. (Richard C.); Maurice, S. (Sylvestre) et al.
Partner: UNT Libraries Government Documents Department

Distribution of iron&titanium on the lunar surface from lunar prospector gamma ray spectra

Description: Gamma ray pulse height spectra acquired by the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) contain information on the abundance of major elements in the lunar surface, including O, Si, Ti, Al, Fe, Mg, Ca, K, and Th. With the exception of Th and K, prompt gamma rays produced by cosmic ray interactions with surface materials are used to determine elemental abundance. Most of these gamma rays are produced by inelastic scattering of fast neutrons and by neutron capture. The production of neutron-induced gamma rays reaches a maximum deep below the surface (e.g. {approx}140 g/cm{sup 2} for inelastic scattering and {approx}50 g/cm{sup 2} for capture). Consequently, gamma rays sense the bulk composition of lunar materials, in contrast to optical methods [e.g. Clementine Spectral Reflectance (CSR)], which only sample the top few microns. Because most of the gamma rays are produced deep beneath the surface, few escape unscattered and the continuum of scattered gamma rays dominates the spectrum. In addition, due to the resolution of the spectrometer, there are few well-isolated peaks and peak fitting algorithms must be used to deconvolve the spectrum in order to determine the contribution of individual elements.
Date: January 1, 2001
Creator: Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Lawrence, David J. (David Jeffery),; Elphic, R. C. (Richard C.); Gasnault, O. M. (Olivier M.); Maurice, S. (Sylvestre) et al.
Partner: UNT Libraries Government Documents Department

Regional elemental abundances within South Pole-Aitken basin as measured with lunar prospector gamma-ray spectrometer data.

Description: South Pole-Aitken (SPA) basin has been a target of intense study since it is one of the largest impact basins in the solar system. It is thought that SPA basin excavated deep into the lunar crust and possibly even the mantle. Such conclusions have been supported by the observed mafic and thorium composition anomalies seen across the entire basin. One of the major goals of lunar and planetary science has been to measure and understand the composition of the non-mare materials within SPA basin. It is expected that this information will help to increase our understanding of the formation and differentiation processes that occurred early on the Moon.
Date: January 1, 2003
Creator: Lawrence, David J. (David Jeffery),; Pieters, Carlé M.; Elphic, R. C. (Richard C.); Gasnault, O. M. (Olivier M.); Prettyman, T. H. (Thomas H.) & Feldman, W. C. (William C.)
Partner: UNT Libraries Government Documents Department

CdZnTe gamma ray spectrometer for orbital gamma ray spectroscopy.

Description: We present the design and analysis of a new gamma ray spectrometer for planetary science that uses an array of CdZnTe detectors to achieve the detection efficiency needed for orbital measurements. The use of CdZnTe will provide significantly improved pulse height resolution relative to scintillation-based detectors, with commensurate improvement in the accuracy of elemental abundances determined by gamma ray and neutron spectroscopy. The spectrometer can be flown either on the instrument deck of the spacecraft or on a boom. For deck-mounted systems, a BGO anticoincidence shield is included in the design to suppress the response of the CdZnTe detector to gamma rays that originate in the spacecraft. The BGO shield also serves as a backup spectrometer, providing heritage from earlier planetary science missions and reducing the risk associated with the implementation of new technology.
Date: January 1, 2001
Creator: Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Fuller, K. R. (Kenneth R.); Storms, S. A. (Steven A.); Soldner, S. A.; Lawrence, David J. (David Jeffery), et al.
Partner: UNT Libraries Government Documents Department

CdZnTe gamma ray spectrometer for orbital planetary missions

Description: 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.
Date: January 1, 2001
Creator: Feldman, W. C. (William C.); Storms, S. A. (Steven A.); Fuller, K. R. (Kenneth R.); Moss, C. E. (Calvin E.); Browne, M. C. (Michael C.); Lawrence, David J. (David Jeffery), et al.
Partner: UNT Libraries Government Documents Department

Evidence of water ice near the lunar poles

Description: Lunar Prospector epithermal neutron data were studied to evaluate the probable chemical state of enhanced hydrogen, [H], reported previously to be near both lunar poles [1,2]. Improved versions of thermal and epithermal neutron data were developed for this purpose. Most important is the improved spatial resolution obtained by using shortened integration times. A new data set was created, Epi* = [Epithermal - 0.057 x Thermal], to reduce effects of composition variations other than those due to hydrogen. The Epi* counting rates are generally low near both lunar poles and high over terrane near recent impact events such as Tycho and Jackson. However, other lunar features are also associated with high Epi* rates, which represent a wide range of terrane types that seem to have little in common. If we postulate that one property all bright Epi* features do have in common is low [H], then measured Epi* counting rates appear to be quantitatively self consistent. If we assume that [H]=O above the top 98th percentile of Epi* counting rates at 2{sup o} x 2{sup o} spatial resolution, then [H]{sub ave} = 55 ppm for latitudes equatorward of [75{sup o}]. This value is close to the average found in returned lunar soil samples, [H]{sub ave} {approx} 50 ppm [3]. Using the foregoing physical interpretation of Epi* counting rates, we find that the Epi* counts within most of the large craters poleward of {+-}70{sup o} are higher, and therefore [H] is lower, than that in neighboring inter-crater plains, as shown in Figure 1. Fourteen of these craters that have areas larger than the LP epithermal spatial resolution (55 km diameter at 30 km altitude), were singled out for study. [H] is generally found to increase with decreasing distance from the poles (hence decreasing temperature). However, quantitative estimates of the diffusivity of hydrogen ...
Date: January 1, 2001
Creator: Feldman, W. C. (William C.); Maurice, S. (Sylvestre); Lawrence, David J. (David Jeffery),; Little, R. C. (Robert C.); Lawrence, S. L. (Stefanie L.); Gasnault, O. M. (Olivier M.) et al.
Partner: UNT Libraries Government Documents Department

Mid-latitude composition of mars from thermal and epithermal neutrons

Description: Epithermal neutron data acquired by Mars Odyssey have been analyzed to determine global maps of water-equivalent hydrogen abundance. By assuming that hydrogen was distributed uniformly with depth within the surface, a map of minimum water abundance was obtained. The addition of thermal neutrons to this analysis could provide information needed to determine water stratigraphy. For example, thermal and epithermal neutrons have been used together to determine the depth and abundance of waterequivalent hydrogen of a buried layer in the south polar region. Because the emission of thermal neutrons from the Martian surface is sensitive to absorption by elements other than hydrogen, analysis of stratigraphy requires that the abundance of these elements be known. For example, recently published studies of the south polar region assumed that the Mars Pathfinder mean soil composition is representative of the regional soil composition, This assumption is partially motivated by the fact that Mars appears to have a well-mixed global dust cover and that the Pathfinder soil composition is representative of the mean composition of the Martian surface. In this study, we have analyzed thermal and epithermal neutron data measured by the neutron spectrometer subsystem of the gamma ray spectrometer to determine the spatial distribution of the composition of elements other than hydrogen. We have restricted our analysis to mid-latitude regions for which we have corrected the neutron counting data for variations in atmospheric thickness.
Date: January 1, 2003
Creator: Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Elphic, R. C. (Richard C.); Boynton, W. V. (William V.); Bish, D. L. (David L.); Vaniman, D. T. (David T.) et al.
Partner: UNT Libraries Government Documents Department