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David J. Lawrence - One of the best experts on this subject based on the ideXlab platform.
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Measurement of the Free Neutron Lifetime using the Neutron Spectrometer on NASA's Lunar Prospector Mission.
arXiv: Nuclear Experiment, 2020Co-Authors: John Wilson, David J. Lawrence, Patrick N. Peplowski, Vincent R. Eke, J. A. KegerreisAbstract:We use data from the Lunar Prospector Neutron Spectrometer to make the second space-based measurement of the free neutron lifetime. The mean lifetime to $\beta$-decay of free neutrons is an important parameter for several areas of physics. However, current laboratory measurements of this lifetime, applying two independent approaches, differ by over 4$\sigma$. Planetary bodies are a source of neutrons due to their creation in the spallation of nuclei by galactic cosmic rays. Using data from Lunar Prospector, which orbited the Moon in 1998-1999, our analysis yields a neutron lifetime of $\tau_n=900 {\:^{+40}_{-50\:\text{stat}}}\pm 17_\text{syst}$ s, which is within 1$\sigma$ of the accepted value. This measurement expands the range of planetary bodies where the neutron lifetime has been quantified from space, and by extending the modeling to account for non-uniform elemental composition mitigates a significant source of systematic uncertainty on the previous space-based lifetime measurement. This modeling provides a key step for space-based neutron lifetime measurements towards the ultimate goal of reducing the magnitude of the systematics on a future space-measurement to the level of those seen in laboratory-based experiments.
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Image Reconstruction Techniques in Neutron and Gamma Ray Spectroscopy: Improving Lunar Prospector Data
Journal of Geophysical Research: Planets, 2018Co-Authors: John Wilson, David J. Lawrence, Patrick N. Peplowski, Vincent R. Eke, Joshua T.s. Cahill, Richard Massey, L. F. A. TeodoroAbstract:We present improved resolution maps of the Lunar Prospector Neutron Spectrometer thermal, epithermal, and fast neutron data and gamma ray spectrometer Th‐line fluxes via global application of pixon image reconstruction techniques. With the use of mock data sets, we show that the pixon image reconstruction method compares favorably with other methods that have been used in planetary neutron and gamma ray spectroscopy. The improved thermal neutron maps are able to clearly distinguish variations in composition across the Lunar surface, including within the Lunar basins of Hertzsprung and Schrodinger. The improvement in resolution reveals a correlation between albedo and thermal neutron flux within the basins. The consequent increase in dynamic range confirms that Hertzsprung basin contains one of the most anorthositic parts of the Lunar crust, including nearly pure anorthite over a region tens of kilometers in diameter. At Orientale, the reconstructed epithermal neutron data show broad overlap with circular polarization ratio but there remains a mismatch between measures of regolith maturity that sample the surface and those that probe the near subsurface, which is consistent with a complex layering scenario.
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The Local-time variations of Lunar Prospector epithermal-neutron data
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: F. A. Luís, David J. Lawrence, William C. Feldman, R. C. Elphic, Sylvestre Maurice, Vincent R. Eke, Teodoro, Matthew A. Siegler, David A. PaigeAbstract:We assess local-time variations of epithermal-neutron count rates measured by the Lunar Prospector Neutron Spectrometer. We investigate the nature of these variations and find no evidence to support the idea that such variations are caused by diurnal variations of hydrogen concentration across the Lunar surface. Rather we find an anticorrelation between instrumental temperature and epithermal-neutron count rate. We have also found that the measured counts are dependent on the temperatures of the top decimeters of the Lunar subsurface as constrained by the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment temperature measurements. Finally, we have made the first measurement of the effective leakage depth for epithermal-neutrons of ~20 cm.
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New insights into the global composition of the Lunar surface from high‐energy gamma rays measured by Lunar Prospector
Journal of Geophysical Research: Planets, 2013Co-Authors: Patrick N. Peplowski, David J. LawrenceAbstract:[1] An analysis of the Lunar gamma-ray spectrum as measured by the Lunar Prospector Gamma-Ray Spectrometer has revealed that 8–8.9 MeV gamma rays contain information about the elemental composition of near-surface materials. These high-energy gamma rays are found to be primarily sensitive to the total Fe and Mg content of the surface, although other elements also contribute. This information has been used to identify several regions with unique compositions, including the Hertzsprung and Orientale basins. A method for deriving global Mg abundances from high-energy gamma-ray measurements is presented. The physical mechanism for high-energy gamma-ray production is proposed to be radiation produced during the decay of galactic cosmic ray produced pions within the Lunar surface. Laboratory measurements of pion production cross sections are found to be consistent with the empirically derived relationship between the Lunar Fe, Mg, and Ti abundances and the measured high-energy gamma-ray count rates.
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Operation of a 3He proportional counter in the Ganymede radiation environment
Planetary and Space Science, 2012Co-Authors: Patrick N. Peplowski, David J. Lawrence, William C. Feldman, Peter D. Hepplewhite, Charles A. HibbittsAbstract:Abstract Neutron spectroscopy has the potential to address many of the scientific objectives of the Jupiter Ganymede Orbiter mission. The most significant challenge is understanding the response of a neutron spectrometer to the intense radiation environment around Ganymede. This study uses data from the Lunar Prospector Neutron Spectrometer to benchmark simulations of the performance of a similar instrument in Ganymede orbit. A solar particle event observed by the Lunar Prospector Neutron Spectrometer serves as a surrogate for the charged particle environment around Ganymede, facilitating a study of the instrument response using data acquired in an environment very similar to the radiation environment found at Ganymede. Based on the conclusions of this study, modifications to a Lunar Prospector-style neutron spectrometer are suggested to allow for the operation of such an instrument in Ganymede orbit. Simulations of the expected signal, based on current models of the surface composition, show this instrument would be capable of compositionally characterizing the nature and extent of surface ice deposits.
R. C. Elphic - One of the best experts on this subject based on the ideXlab platform.
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The Local-time variations of Lunar Prospector epithermal-neutron data
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: F. A. Luís, David J. Lawrence, William C. Feldman, R. C. Elphic, Sylvestre Maurice, Vincent R. Eke, Teodoro, Matthew A. Siegler, David A. PaigeAbstract:We assess local-time variations of epithermal-neutron count rates measured by the Lunar Prospector Neutron Spectrometer. We investigate the nature of these variations and find no evidence to support the idea that such variations are caused by diurnal variations of hydrogen concentration across the Lunar surface. Rather we find an anticorrelation between instrumental temperature and epithermal-neutron count rate. We have also found that the measured counts are dependent on the temperatures of the top decimeters of the Lunar subsurface as constrained by the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment temperature measurements. Finally, we have made the first measurement of the effective leakage depth for epithermal-neutrons of ~20 cm.
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the average water concentration within cabeus crater inferences from lro diviner lcross and Lunar Prospector
LPI, 2011Co-Authors: R. C. Elphic, L. F. A. Teodoro, V R Eke, D A Paige, M A Siegler, A. ColapreteAbstract:LRO/DIVINER, LCROSS AND Lunar Prospector. R. C. Elphic, L. F. A. Teodoro, V. R. Eke, David A Paige, Matthew A Siegler, A. Colaprete, Planetary Systems Branch, NASA Ames Research Center, Moffett Field, CA, USA. BAER Institute, NASA Ames Research Center, Moffett Field, CA, USA, Institute for Computational Cosmology, Physics Department, Durham University, Durham, UK, Earth and Space Sciences, UCLA, Los Angeles, CA, USA.
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The Average Water Concentration Within Cabeus Crater: Inferences from LRO/Diviner, LCROSS and Lunar Prospector
2011Co-Authors: R. C. Elphic, Vincent R. Eke, Matthew A. Siegler, David A. Paige, L. F. A. Teodoro, A. ColapreteAbstract:LRO/DIVINER, LCROSS AND Lunar Prospector. R. C. Elphic, L. F. A. Teodoro, V. R. Eke, David A Paige, Matthew A Siegler, A. Colaprete, Planetary Systems Branch, NASA Ames Research Center, Moffett Field, CA, USA. BAER Institute, NASA Ames Research Center, Moffett Field, CA, USA, Institute for Computational Cosmology, Physics Department, Durham University, Durham, UK, Earth and Space Sciences, UCLA, Los Angeles, CA, USA.
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Global spatial deconvolution of Lunar Prospector Th abundances
Geophysical Research Letters, 2007Co-Authors: David J. Lawrence, R. C. Elphic, W. C. Feldman, R. C. Puetter, Justin J. Hagerty, Thomas H. Prettyman, Paul D. SpudisAbstract:[1] We have completed the first global spatial deconvolution analysis of planetary gamma-ray data for Lunar Th abundances as measured by the Lunar Prospector Gamma-ray Spectrometer. We tested two different spatial deconvolution techniques – Jansson's method and the Pixon method – and determined that the Pixon method provides superior performance. The final deconvolved map results in a spatial resolution improvement of a factor of 1.5–2. The newly deconvolved data allow us to clearly delineate nearside Th enhancements and depressions, validate enhanced Th abundances associated with specific Lunar red spots, and reveal new details of the Th distribution at the Aristarchus plateau.
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Elemental composition of the Lunar surface: Analysis of gamma ray spectroscopy data from Lunar Prospector
Journal of Geophysical Research: Planets, 2006Co-Authors: Thomas H. Prettyman, David J. Lawrence, R. C. Elphic, W. C. Feldman, Justin J. Hagerty, G. W. Mckinney, David T. VanimanAbstract:[1] Gamma ray spectroscopy data acquired by Lunar Prospector are used to determine global maps of the elemental composition of the Lunar surface. Maps of the abundance of major oxides, MgO, Al2O3, SiO2, CaO, TiO2, and FeO, and trace incompatible elements, K and Th, are presented along with their geochemical interpretation. Linear spectral mixing is used to model the observed gamma ray spectrum for each map pixel. The spectral shape for each elemental constituent is determined by a Monte Carlo radiation transport calculation. Linearization of the mixing model is accomplished by scaling the spectral shapes with Lunar surface parameters determined by neutron spectroscopy, including the number density of neutrons slowing down within the surface and the effective atomic mass of the surface materials. The association of the highlands with the feldspathic Lunar meteorites is used to calibrate the mixing model and to determine backgrounds. A linear least squares approach is used to unmix measured spectra to determine the composition of each map pixel. The present analysis uses new gamma ray production cross sections for neutron interactions, resulting in improved accuracy compared to results previously submitted to the Planetary Data System. Systematic variations in Lunar composition determined by the spectral unmixing analysis are compared with the Lunar soil sample and meteorite collections. Significant results include improved accuracy for the abundance of Th and K in the highlands; identification of large regions, including western Procellarum, that are not well represented by the sample collection; and the association of relatively high concentrations of Mg with KREEP-rich regions on the Lunar nearside, which may have implications for the concept of an early magma ocean.
W. C. Feldman - One of the best experts on this subject based on the ideXlab platform.
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Global spatial deconvolution of Lunar Prospector Th abundances
Geophysical Research Letters, 2007Co-Authors: David J. Lawrence, R. C. Elphic, W. C. Feldman, R. C. Puetter, Justin J. Hagerty, Thomas H. Prettyman, Paul D. SpudisAbstract:[1] We have completed the first global spatial deconvolution analysis of planetary gamma-ray data for Lunar Th abundances as measured by the Lunar Prospector Gamma-ray Spectrometer. We tested two different spatial deconvolution techniques – Jansson's method and the Pixon method – and determined that the Pixon method provides superior performance. The final deconvolved map results in a spatial resolution improvement of a factor of 1.5–2. The newly deconvolved data allow us to clearly delineate nearside Th enhancements and depressions, validate enhanced Th abundances associated with specific Lunar red spots, and reveal new details of the Th distribution at the Aristarchus plateau.
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Elemental composition of the Lunar surface: Analysis of gamma ray spectroscopy data from Lunar Prospector
Journal of Geophysical Research: Planets, 2006Co-Authors: Thomas H. Prettyman, David J. Lawrence, R. C. Elphic, W. C. Feldman, Justin J. Hagerty, G. W. Mckinney, David T. VanimanAbstract:[1] Gamma ray spectroscopy data acquired by Lunar Prospector are used to determine global maps of the elemental composition of the Lunar surface. Maps of the abundance of major oxides, MgO, Al2O3, SiO2, CaO, TiO2, and FeO, and trace incompatible elements, K and Th, are presented along with their geochemical interpretation. Linear spectral mixing is used to model the observed gamma ray spectrum for each map pixel. The spectral shape for each elemental constituent is determined by a Monte Carlo radiation transport calculation. Linearization of the mixing model is accomplished by scaling the spectral shapes with Lunar surface parameters determined by neutron spectroscopy, including the number density of neutrons slowing down within the surface and the effective atomic mass of the surface materials. The association of the highlands with the feldspathic Lunar meteorites is used to calibrate the mixing model and to determine backgrounds. A linear least squares approach is used to unmix measured spectra to determine the composition of each map pixel. The present analysis uses new gamma ray production cross sections for neutron interactions, resulting in improved accuracy compared to results previously submitted to the Planetary Data System. Systematic variations in Lunar composition determined by the spectral unmixing analysis are compared with the Lunar soil sample and meteorite collections. Significant results include improved accuracy for the abundance of Th and K in the highlands; identification of large regions, including western Procellarum, that are not well represented by the sample collection; and the association of relatively high concentrations of Mg with KREEP-rich regions on the Lunar nearside, which may have implications for the concept of an early magma ocean.
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improved modeling of Lunar Prospector neutron spectrometer data implications for hydrogen deposits at the Lunar poles
Journal of Geophysical Research, 2006Co-Authors: D J Lawrence, R. C. Elphic, W. C. Feldman, G. W. Mckinney, S. Maurice, J J Hagerty, T H PrettymanAbstract:[1] New models have been computed for the Lunar Prospector (LP) thermal and epithermal neutron counting rates using the particle transport code MCNPX. This work improves upon previous studies by using one code to model the neutron production, transport, and detection processes, and by examining the sensitivity of epithermal neutrons to elements other than hydrogen. Our modeling results for standard anhydrous Lunar soils show that when hydrogen is not included in a soil, epithermal neutrons are most sensitive to variations in the abundances of Fe, Gd, and Sm, which is consistent with measured epithermal neutron data. We use our current modeling results, in conjunction with known mineral compositions of Lunar soils and other Lunar global data sets to conclude that the best explanation for a decrease in the counting rate of epithermal neutrons near both Lunar poles is the presence of hydrogen. We have further concluded that the average hydrogen abundance near both Lunar poles is 100–150 ppm and is likely buried by 10 ± 5 cm of dry Lunar soil, a result that is consistent with previous studies. The localized hydrogen abundance for small (<20 km) areas of permanently shaded regions remains highly uncertain and could range from 200 ppm H up to 40 wt% H2O in some isolated regions.
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Improved modeling of Lunar Prospector neutron spectrometer data: Implications for hydrogen deposits at the Lunar poles
Journal of Geophysical Research, 2006Co-Authors: David J. Lawrence, R. C. Elphic, Sylvestre Maurice, W. C. Feldman, Justin J. Hagerty, G. W. Mckinney, Thomas H. PrettymanAbstract:[1] New models have been computed for the Lunar Prospector (LP) thermal and epithermal neutron counting rates using the particle transport code MCNPX. This work improves upon previous studies by using one code to model the neutron production, transport, and detection processes, and by examining the sensitivity of epithermal neutrons to elements other than hydrogen. Our modeling results for standard anhydrous Lunar soils show that when hydrogen is not included in a soil, epithermal neutrons are most sensitive to variations in the abundances of Fe, Gd, and Sm, which is consistent with measured epithermal neutron data. We use our current modeling results, in conjunction with known mineral compositions of Lunar soils and other Lunar global data sets to conclude that the best explanation for a decrease in the counting rate of epithermal neutrons near both Lunar poles is the presence of hydrogen. We have further concluded that the average hydrogen abundance near both Lunar poles is 100–150 ppm and is likely buried by 10 ± 5 cm of dry Lunar soil, a result that is consistent with previous studies. The localized hydrogen abundance for small (
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reduction of neutron data from Lunar Prospector
Journal of Geophysical Research, 2004Co-Authors: S. Maurice, R. C. Elphic, W. C. Feldman, D J Lawrence, Olivier GasnaultAbstract:[1] From January 1998 to July 1999, Lunar Prospector continuously measured the leakage flux of neutrons from the Moon in four distinct energy ranges from 0 eV to 8 MeV. These measurements were made using two 3He tubes within the Neutron Spectrometer (NS) and the anticoincidence shield of the Gamma-Ray Spectrometer (GRS). This publication details the reduction of raw neutron data (level 0) to develop four maps of neutron counting rates, which can be interpreted in terms of elemental composition of the Lunar regolith. Details are given to convert level 0 data into level 1 data, where corrupted and unusable records have been removed because of transmission errors, solar energetic-particle events, or cross-talk with other instruments. At level 2, time series data have been corrected for observational biases and variations of the response function of the instruments. At level 3 the highest-quality neutron data (low-altitude, high time resolution) are mapped onto the Moon. The main characteristics of each map are, for thermal neutrons, energy range 0–0.4 eV, dynamic range 95%, precision 2.7%, and half width at half maximum (HWHM) resolution 23 km, in units of counts/8-s; for epithermal neutrons, energy range 0.4 eV < E < 0.7 MeV, dynamic range 15%, precision 1%, and HWHM resolution 22 km, in units of counts/8-s; for moderated neutrons, energy range 0–0.8 MeV, dynamic range 15%, precision 1.8%, and HWHM resolution <45 km, in units of counts/32-s; and for fast neutrons, energy range 0.8–8 MeV, dynamic range 30%, precision 1.6%, and HWHM resolution 23 km, in units of counts/32-s. All maps are normalized to 30 km altitude, at the equator; and to the flux of cosmic rays in January 1998. They are presented as 720 × 360 arrays equally spaced in latitude and longitude. Results are reproducible from raw data that are available at the Planetary Data System (PDS), together with guidance and numerical values in this publication.
Sylvestre Maurice - One of the best experts on this subject based on the ideXlab platform.
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The Local-time variations of Lunar Prospector epithermal-neutron data
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: F. A. Luís, David J. Lawrence, William C. Feldman, R. C. Elphic, Sylvestre Maurice, Vincent R. Eke, Teodoro, Matthew A. Siegler, David A. PaigeAbstract:We assess local-time variations of epithermal-neutron count rates measured by the Lunar Prospector Neutron Spectrometer. We investigate the nature of these variations and find no evidence to support the idea that such variations are caused by diurnal variations of hydrogen concentration across the Lunar surface. Rather we find an anticorrelation between instrumental temperature and epithermal-neutron count rate. We have also found that the measured counts are dependent on the temperatures of the top decimeters of the Lunar subsurface as constrained by the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment temperature measurements. Finally, we have made the first measurement of the effective leakage depth for epithermal-neutrons of ~20 cm.
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Improved modeling of Lunar Prospector neutron spectrometer data: Implications for hydrogen deposits at the Lunar poles
Journal of Geophysical Research, 2006Co-Authors: David J. Lawrence, R. C. Elphic, Sylvestre Maurice, W. C. Feldman, Justin J. Hagerty, G. W. Mckinney, Thomas H. PrettymanAbstract:[1] New models have been computed for the Lunar Prospector (LP) thermal and epithermal neutron counting rates using the particle transport code MCNPX. This work improves upon previous studies by using one code to model the neutron production, transport, and detection processes, and by examining the sensitivity of epithermal neutrons to elements other than hydrogen. Our modeling results for standard anhydrous Lunar soils show that when hydrogen is not included in a soil, epithermal neutrons are most sensitive to variations in the abundances of Fe, Gd, and Sm, which is consistent with measured epithermal neutron data. We use our current modeling results, in conjunction with known mineral compositions of Lunar soils and other Lunar global data sets to conclude that the best explanation for a decrease in the counting rate of epithermal neutrons near both Lunar poles is the presence of hydrogen. We have further concluded that the average hydrogen abundance near both Lunar poles is 100–150 ppm and is likely buried by 10 ± 5 cm of dry Lunar soil, a result that is consistent with previous studies. The localized hydrogen abundance for small (
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Recent outgassing from the Lunar surface: The Lunar Prospector Alpha Particle Spectrometer
Journal of Geophysical Research, 2005Co-Authors: S. L. Lawson, David J. Lawrence, William C. Feldman, R. C. Elphic, K. R. Moore, Richard D. Belian, Sylvestre MauriceAbstract:[1] The Lunar Prospector Alpha Particle Spectrometer (APS) was designed to detect characteristic-energy alpha particles from the decay of Rn-222, Po-218, and Po-210 and to therefore map sites of radon release on the Lunar surface. These three nuclides are radioactive daughters from the decay of U-238; hence the background level of alpha particle activity is a function of the Lunar crustal uranium distribution. Radon reaches the Lunar surface either at areas of high soil porosity or where fissures release the trapped gases in which radon is entrained. Once released, the radon spreads out by “bouncing” across the surface on ballistic trajectories in a random-walk process. The half-life of Rn-222 allows the gas to spread out by several hundred kilometers before it decays (depositing approximately half of the Po-218 recoil nuclides on the Lunar surface) and allows the APS to detect gas release events up to several days after they occur. The long residence time of the Pb-210 precursor to Po-210 allows the mapping of gas vents which have been active over the last approximately 60 years. The APS found only a faint indication of Po-218 alpha particles. However, the Rn-222 alpha particle map shows that radon gas was emanating from the vicinity of craters Aristarchus and Kepler at the time of Lunar Prospector. The Po-210 alpha particle distribution reveals a variability in time and space of Lunar gas release events. Po-210 and Rn-222 detections are associated with both thorium enhancements and Lunar pyroclastic deposits.
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Reduction of neutron data from Lunar Prospector : Space simulations in laboratory: Experiments, instrumentation, and modeling
Journal of Geophysical Research, 2004Co-Authors: Sylvestre Maurice, David J. Lawrence, William C. Feldman, R. C. Elphic, Olivier GasnaultAbstract:[1] From January 1998 to July 1999, Lunar Prospector continuously measured the leakage flux of neutrons from the Moon in four distinct energy ranges from 0 eV to 8 MeV. These measurements were made using two 3 He tubes within the Neutron Spectrometer (NS) and the anticoincidence shield of the Gamma-Ray Spectrometer (GRS). This publication details the reduction of raw neutron data (level 0) to develop four maps of neutron counting rates, which can be interpreted in terms of elemental composition of the Lunar regolith. Details are given to convert level 0 data into level I data, where corrupted and unusable records have been removed because of transmission errors, solar energetic-particle events, or cross-talk with other instruments. At level 2, time series data have been corrected for observational biases and variations of the response function of the instruments. At level 3 the highest-quality neutron data (low-altitude, high time resolution) are mapped onto the Moon. The main characteristics of each map are, for thermal neutrons, energy range 0-0.4 eV, dynamic range 95%, precision 2.7%, and half width at half maximum (HWHM) resolution 23 km, in units of counts/8-s; for epithermal neutrons, energy range 0.4 eV < E < 0.7 MeV, dynamic range 15%, precision 1%, and HWHM resolution 22 km, in units of counts/8-s; for moderated neutrons, energy range 0-0.8 MeV, dynamic range 15%, precision 1.8%, and HWHM resolution
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Reduction of neutron data from Lunar Prospector
Journal of Geophysical Research, 2004Co-Authors: Sylvestre Maurice, David J. Lawrence, R. C. Elphic, W. C. Feldman, Olivier GasnaultAbstract:[1] From January 1998 to July 1999, Lunar Prospector continuously measured the leakage flux of neutrons from the Moon in four distinct energy ranges from 0 eV to 8 MeV. These measurements were made using two 3He tubes within the Neutron Spectrometer (NS) and the anticoincidence shield of the Gamma-Ray Spectrometer (GRS). This publication details the reduction of raw neutron data (level 0) to develop four maps of neutron counting rates, which can be interpreted in terms of elemental composition of the Lunar regolith. Details are given to convert level 0 data into level 1 data, where corrupted and unusable records have been removed because of transmission errors, solar energetic-particle events, or cross-talk with other instruments. At level 2, time series data have been corrected for observational biases and variations of the response function of the instruments. At level 3 the highest-quality neutron data (low-altitude, high time resolution) are mapped onto the Moon. The main characteristics of each map are, for thermal neutrons, energy range 0–0.4 eV, dynamic range 95%, precision 2.7%, and half width at half maximum (HWHM) resolution 23 km, in units of counts/8-s; for epithermal neutrons, energy range 0.4 eV < E < 0.7 MeV, dynamic range 15%, precision 1%, and HWHM resolution 22 km, in units of counts/8-s; for moderated neutrons, energy range 0–0.8 MeV, dynamic range 15%, precision 1.8%, and HWHM resolution
Alan B. Binder - One of the best experts on this subject based on the ideXlab platform.
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Global mapping of Lunar crustal magnetic fields by Lunar Prospector
Icarus, 2008Co-Authors: D L Mitchell, J S Halekas, S. Frey, Mario H. Acuña, Lon L. Hood, Robert P. Lin, Alan B. BinderAbstract:Abstract The Lunar Prospector Electron Reflectometer has obtained the first global map of Lunar crustal magnetic fields, revealing that the effects of basin-forming impacts dominate the large-scale distribution of remanent magnetic fields on the Moon. The weakest surface magnetic fields ( 40 nT) are diametrically opposite to these same basins. This pattern is present though less pronounced for several other post-Nectarian impact basins larger than 500 km in diameter. The reduced strength and clarity of the pattern for older basins may be attributed to: (1) demagnetization from many smaller impacts, which erases antipodal magnetic signatures over time, (2) superposition effects from other large impacts, and (3) variation in the strength of the ambient magnetizing field. The absence of fringing fields stronger than 1 nT around the perimeter of the Imbrium basin or associated with craters within the basin implies that any uniform magnetization of the impact melt must be weaker than ∼ 10 −6 G cm3 g−1. This limits the strength of any steady ambient magnetic field to no more than ∼0.1 Oe at the Lunar surface while the basin cooled for tens of millions of years following the Imbrium impact 3.8 billion years ago.
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LIBRARY LEAST SQUARES ANALYSIS OF Lunar Prospector GAMMA RAY SPECTRA.
2002Co-Authors: Thomas H. Prettyman, David J. Lawrence, William C. Feldman, R. C. Elphic, Alan B. Binder, Sylvestre Maurice, Olivier Gasnault, G. W. Mckinney, K. R. MooreAbstract:Gamma rays are produced in the lu-nar surface by cosmic ray interactions and by the decay of radioisotopes. The gamma ray spectrum measured from orbit contains information on the abundance of major elements, including O, Si, Ti, Al, Fe, Mg, and Ca, and radioactive elements, including Th, U, and K. The Lunar Prospector mission acquired gamma ray and neutron spectra at two altitudes (30- and 100-km) over the whole moon. We have binned these spectra on equal area squares to produce data sets from which maps of elemental abundance can be determined. The Lunar Prospector gamma ray spectometer (GRS) consisted of a BGO scintillation detector with a plastic-scintillator anticoincidence shield. The pulse height resolution of the spectrometer was ~13% full-width-at-half-maximum at 662 keV. At this resolution, most spectral features included contributions from mul-tiple elements. Maps of Th have been made using the well-resolved 2.61 MeV gamma ray.[1] Maps of Fe have been made by analyzing net count rates in the region above 7.5 MeV.[2] Contributions from Al to this region were ignored, which may influence the ac-curacy of Fe abundance in regions with low Fe. Maps of Fe and Ti have been made by deconvolution of the spectrum above 5.5 MeV.[3] We have extended the deconvolution method to 700 keV, using a library least squares technique, which enables us to determine the abundance of all major- and radioactive-elements.
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Lunar Prospector neutron spectrometer constraints on TiO2
Journal of Geophysical Research, 2002Co-Authors: R. C. Elphic, David J. Lawrence, B L Barraclough, Sylvestre Maurice, Paul G. Lucey, W. C. Feldman, Olivier Gasnault, D. T. Blewett, Alan B. BinderAbstract:[1] Lunar Prospector neutron spectrometer measurements of the epithermal and thermal neutron leakage fluxes are used to provide constraints on TiO2 abundances in Lunar surface materials. We use FeO abundance estimates based on both Clementine spectral reflectance techniques and preliminary Lunar Prospector gamma ray spectrometer determinations to first establish a model thermal neutron absorption due to all major elements except titanium. Then we remove the additional absorbing effects due to the rare earth elements gadolinium and samarium by using Lunar Prospector gamma ray spectrometer thorium abundances as a rare earth element proxy. The result can be compared to the ratio of epithermal to thermal neutron fluxes, which point to the presence of the additional thermal neutron absorber, titanium. We can derive abundance estimates of TiO2 and compare to other estimates derived spectroscopically. Our results show a significantly lower abundance of TiO2 than has been derived using Clementine data.
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Global distribution of Lunar composition: New results from Lunar Prospector
Journal of Geophysical Research, 2002Co-Authors: W. C. Feldman, David J. Lawrence, R. C. Elphic, Sylvestre Maurice, Paul G. Lucey, Olivier Gasnault, Alan B. BinderAbstract:[1] Maps of thorium [Th], [FeO], the ratio of epithermal to thermal neutrons (E/T), and fast neutrons (FN) from Lunar Prospector were studied to determine their global distribution on the Moon. These distributions are compared to that of the 750 nm Lunar albedo from Clementine to aid in their interpretation. All distributions were parameterized using a spherical harmonic expansion out to order l = 30. Resultant harmonic coefficients generally decrease with increasing l value as a power law in l for all five variables. The axes of all dipole components (l = 1) cluster closely about a centroid given by +14.1° latitude and 16.4° west longitude. This location is very close to the symmetry axes of their quadrupole components (l = 2), which cluster about a centroid given by +24.6° latitude and 25.1° west longitude. Both centroids are near the center of a suggested Procellarum basin, given by Whitaker [1981] at +23° latitude and 15° west longitude. This suggestion is strengthened by a sharp decrease of the intensities of all three variables at ∼50° from the centroids, which is close to the boundary of the putative Procellarum basin. The coincidence of the global concentration of heat-producing elements (through [Th]) and mare deposits on the Lunar surface (through [FeO], [T/E], and [FN]) with the circular outline of a putative Procellarum basin suggests that the events that were responsible for producing Oceanus Procellarum (perhaps a single giant impact) must figure importantly in shaping the global distribution of surface composition. A second, apparently older circular structure having its center near −5° latitude and 65° east longitude and a radius of 50° is also hinted at in the data.
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Mapping of crustal magnetic anomalies on the Lunar near side by the Lunar Prospector electron reflectometer
Journal of Geophysical Research: Planets, 2001Co-Authors: J S Halekas, S. Frey, Mario H. Acuña, Lon L. Hood, Robert P. Lin, David Mitchell, Alan B. BinderAbstract:Lunar Prospector (LP) electron reflectometer measurements show that surface fields are generally weak in the large mare basalt filled impact basins on the near side but are stronger over highland terranes, especially those lying antipodal to young large impact basins. Between the Imbrium and Nectaris basins, many anomalies correlate with the Cayley and Descartes Formations. Statistical analyses show that the most strongly magnetic nearside terranes are Cayley-type light plains, terra materials, and pre-Imbrian craters. Light plains and terrae include basin impact ejecta as a major component, suggesting that magnetization effects from basin-forming impacts were involved in their formation. The magnetization of pre-Imbrian craters, however, may be evidence of early thermal remanence. Relatively strong, small-scale magnetic anomalies are present over the Reiner Gamma feature on western Oceanus Procellarum and over the Rima Sirsalis rille on the southwestern border of Procellarum. Both Apollo subsatellite and LP data show that the latter anomaly is nearly aligned with the rille, though LP magnetometer and reflectometer data show that the anomaly peak is actually centered over a light plains unit. This anomaly and the Reiner Gamma anomaly are approximately radially aligned with the center of Imbrium, suggesting an association with ejecta from this basin.
