The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
L. D. Cussen - One of the best experts on this subject based on the ideXlab platform.
-
scan profiles for Neutron Spectrometers ii rectangular profile elements by acceptance diagram methods
Journal of Applied Crystallography, 2003Co-Authors: L. D. CussenAbstract:The recent development of Neutron collimators with rectangular transmission profiles (intensity versus angular divergence) extends hope of improved count rates on Neutron scattering instruments. It is usually assumed that a more effective use of beam angular spread in these devices should increase count rates by about a factor of two. However, real beams have both angular and wavevector spread and both these spreads are governed by the allowed collimation. In this extended view, the gains from ideal rectangular-profile elements (angle filters) are shown to be much larger (about a factor of four). The mirror reflections used to achieve the rectangular profiles in real devices complicate the resolution effects. Specifically, the reflections disturb the wavevector–angular divergence correlation in the beams, leading to unusual peak shapes characterized by triple peaks on powder diffractometers. Thus, these reflecting collimators are likely to be universally useful only before the monochromator and immediately preceding the detector, where wavevector–angle correlations have no effect. This reduces the potential gains to a factor of two or so. Note that the gains are as previously expected but for quite different reasons than imagined. This remains a very significant gain in a field where most work is intensity-limited.
-
scan profiles for Neutron Spectrometers iii rectangular profile elements by numerical methods
Journal of Applied Crystallography, 2003Co-Authors: L. D. Cussen, A R WildesAbstract:Newly developed reflecting Neutron collimators promise increased detector count rates in a field where most work is intensity-limited. The effects of such elements on instrument resolution are complicated and appear to be even more subtle than previously imagined. Numerical tests using the McSTAS ray-tracing program (http://Neutron.risoe.dk/mcstas) are reported which support and extend the recent analysis of these effects. If reflecting collimators are used in all instrument positions they give unusual scan profiles. Using reflecting collimators only before the monochromator and immediately before the detector has no deleterious resolution effects and increases count rates by a factor of more than two on powder diffractometers.
-
Scan profiles for Neutron Spectrometers. I. Gaussian-profile elements by acceptance-diagram methods
Journal of Applied Crystallography, 2003Co-Authors: L. D. CussenAbstract:`Acceptance diagrams' are a powerful graphical method of describing beam characteristics on Neutron scattering instruments. Recent examples of the technique have used hypothetical rectangular-profile beam elements, not the conventional Gaussian profiles, to clarify the description. This article develops the method for Gaussian-profile beam elements and shows that it gives identical results to accepted techniques. Direct expressions are presented for scan profiles, their widths and intensities for both powder diffractometers and three-axis Spectrometers. This work gives some necessary background and therefore forms the first part of a discussion of the resolution effects of the new reflecting Soller collimators for Neutrons.
Paul G. Lucey - One of the best experts on this subject based on the ideXlab platform.
-
Revised mineral and Mg# maps of the Moon from integrating results from the Lunar Prospector Neutron and gamma-ray Spectrometers with Clementine spectroscopy
American Mineralogist, 2015Co-Authors: S. T. Crites, Paul G. LuceyAbstract:Mineralogical measurements from spectral remote sensing and remote geochemical measurements from gamma-ray and Neutron Spectrometers are complementary data sets that have been used together successfully to study the distributions of iron, titanium, and rare earth elements on the Moon. We compare Neutron and gamma-ray data sets from Lunar Prospector and find them in good agreement with each other within the errors of previously developed equations that relate Neutron flux with geochemistry, but find small adjustments to the nominal values are warranted. We used the Neutron-validated LP GRS oxides to improve Clementine-based global mineral maps. The comparison was enabled by converting the minerals of Lucey (2004) to oxides using stoichiometry and assumptions about Mg#, calcium content of clinopyroxenes, and An#. We find that FeO and Al 2 O 3 derived from the maps of Lucey (2004) do not follow the expected negative correlation seen in lunar samples, but can be brought into agreement with samples and with LP GRS oxides by increasing plagioclase in proportion with orthopyroxene abundance, while simultaneously decreasing Mg#. We interpreted this to mean that plagioclase and orthopyroxene exist in rocks together (as in a noritic rock) with the spectrally difficult to detect plagioclase being masked by the strong spectral signature of the orthopyroxene. We generated a revised set of maps of the major lunar minerals and a map of Mg# for the mafic minerals that are consistent with Lunar Prospector Neutron and gamma-ray spectrometer results and show greatly improved agreement with lunar soil samples over previous global mineral maps from Clementine.
-
revised mineral and mg maps of the moon from integrating results from the lunar prospector Neutron and gamma ray Spectrometers with clementine spectroscopy
American Mineralogist, 2015Co-Authors: S. T. Crites, Paul G. LuceyAbstract:Mineralogical measurements from spectral remote sensing and remote geochemical measurements from gamma-ray and Neutron Spectrometers are complementary data sets that have been used together successfully to study the distributions of iron, titanium, and rare earth elements on the Moon. We compare Neutron and gamma-ray data sets from Lunar Prospector and find them in good agreement with each other within the errors of previously developed equations that relate Neutron flux with geochemistry, but find small adjustments to the nominal values are warranted. We used the Neutron-validated LP GRS oxides to improve Clementine-based global mineral maps. The comparison was enabled by converting the minerals of Lucey (2004) to oxides using stoichiometry and assumptions about Mg#, calcium content of clinopyroxenes, and An#. We find that FeO and Al 2 O 3 derived from the maps of Lucey (2004) do not follow the expected negative correlation seen in lunar samples, but can be brought into agreement with samples and with LP GRS oxides by increasing plagioclase in proportion with orthopyroxene abundance, while simultaneously decreasing Mg#. We interpreted this to mean that plagioclase and orthopyroxene exist in rocks together (as in a noritic rock) with the spectrally difficult to detect plagioclase being masked by the strong spectral signature of the orthopyroxene. We generated a revised set of maps of the major lunar minerals and a map of Mg# for the mafic minerals that are consistent with Lunar Prospector Neutron and gamma-ray spectrometer results and show greatly improved agreement with lunar soil samples over previous global mineral maps from Clementine.
-
Iron abundances on the lunar surface as measured by the Lunar Prospector gamma‐ray and Neutron Spectrometers
Journal of Geophysical Research, 2002Co-Authors: David J. Lawrence, Sylvestre Maurice, W. C. Feldman, Paul G. Lucey, Thomas H. Prettyman, R. C. Elphic, R. C. Little, Alan B. BinderAbstract:[i] Global measurements of iron abundances on the lunar surface are presented using data from the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) and Neutron Spectrometer (NS). In this study, we derive relative iron abundances from the low-altitude, high spatial resolution (∼(45 km) 2 ) LP data using the 7.6 MeV Neutron capture gamma-ray doublet. As part of the LP-GRS analysis, we demonstrate the importance of accounting for variations in Neutron number density across the lunar surface by measuring Neutron fluxes using LP-NS data. In a first step of comparing the LP-GRS data with previously published iron abundances inferred from Clementine Spectral Reflectance (CSR) data, we show that the existing CSR FeO data are nonlinear with respect to the LP relative iron abundances. We use the LP data to linearize the relationship between the CSR and the relative iron values then recalibrate the CSR data to iron abundance using returned soil abundances. We then correlate the CSR data, except for major anomalies, with the LP relative iron measurements to convert the LP data to absolute iron abundances. When we compare the LP-GRS and revised CSR data sets, we find a very good correspondence. There are two locations (Mare Tranquillitatis and South Pole-Aitken (SPA) basin) that show major discrepancies, suggesting that the CSR data are locally overestimating iron abundances. In both these regions, the discrepancies identified by the LP-GRS/CSR comparison are possibly explained by mineralogical differences that are not accounted for in the CSR to FeO calibration. In regards to our understanding of the Moon, the LP data have found the following: (I) There exist large expanses of mare basalt in the western mare regions that have very high iron abundances (22-23 wt.% FeO) that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils, which typically contain a significant amount of highlands contamination. (2) The low iron abundances in the lunar highlands (∼5 FeO wt.%) are consistent with a previous analysis using thermal and epithermal Neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process. (3) The comparison of LP and CSR derived iron abundances suggests that the material within SPA basin is similar to a norite-type rock without an enriched mantle FeO signature. (4) A comparison of LP and CSR data at Tycho Crater shows a large discrepancy such that the CSR data show moderate iron abundances of 8-9 wt.% FeO while the LP data show very low iron abundances of 3-4 wt.% FeO. This discrepancy cannot yet be easily explained by any known process.
-
iron abundances on the lunar surface as measured by the lunar prospector gamma ray and Neutron Spectrometers
Journal of Geophysical Research, 2002Co-Authors: David J. Lawrence, Sylvestre Maurice, W. C. Feldman, Paul G. Lucey, Thomas H. Prettyman, R. C. Elphic, R. C. Little, Alan B. BinderAbstract:[i] Global measurements of iron abundances on the lunar surface are presented using data from the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) and Neutron Spectrometer (NS). In this study, we derive relative iron abundances from the low-altitude, high spatial resolution (∼(45 km) 2 ) LP data using the 7.6 MeV Neutron capture gamma-ray doublet. As part of the LP-GRS analysis, we demonstrate the importance of accounting for variations in Neutron number density across the lunar surface by measuring Neutron fluxes using LP-NS data. In a first step of comparing the LP-GRS data with previously published iron abundances inferred from Clementine Spectral Reflectance (CSR) data, we show that the existing CSR FeO data are nonlinear with respect to the LP relative iron abundances. We use the LP data to linearize the relationship between the CSR and the relative iron values then recalibrate the CSR data to iron abundance using returned soil abundances. We then correlate the CSR data, except for major anomalies, with the LP relative iron measurements to convert the LP data to absolute iron abundances. When we compare the LP-GRS and revised CSR data sets, we find a very good correspondence. There are two locations (Mare Tranquillitatis and South Pole-Aitken (SPA) basin) that show major discrepancies, suggesting that the CSR data are locally overestimating iron abundances. In both these regions, the discrepancies identified by the LP-GRS/CSR comparison are possibly explained by mineralogical differences that are not accounted for in the CSR to FeO calibration. In regards to our understanding of the Moon, the LP data have found the following: (I) There exist large expanses of mare basalt in the western mare regions that have very high iron abundances (22-23 wt.% FeO) that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils, which typically contain a significant amount of highlands contamination. (2) The low iron abundances in the lunar highlands (∼5 FeO wt.%) are consistent with a previous analysis using thermal and epithermal Neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process. (3) The comparison of LP and CSR derived iron abundances suggests that the material within SPA basin is similar to a norite-type rock without an enriched mantle FeO signature. (4) A comparison of LP and CSR data at Tycho Crater shows a large discrepancy such that the CSR data show moderate iron abundances of 8-9 wt.% FeO while the LP data show very low iron abundances of 3-4 wt.% FeO. This discrepancy cannot yet be easily explained by any known process.
A R Wildes - One of the best experts on this subject based on the ideXlab platform.
-
scan profiles for Neutron Spectrometers iii rectangular profile elements by numerical methods
Journal of Applied Crystallography, 2003Co-Authors: L. D. Cussen, A R WildesAbstract:Newly developed reflecting Neutron collimators promise increased detector count rates in a field where most work is intensity-limited. The effects of such elements on instrument resolution are complicated and appear to be even more subtle than previously imagined. Numerical tests using the McSTAS ray-tracing program (http://Neutron.risoe.dk/mcstas) are reported which support and extend the recent analysis of these effects. If reflecting collimators are used in all instrument positions they give unusual scan profiles. Using reflecting collimators only before the monochromator and immediately before the detector has no deleterious resolution effects and increases count rates by a factor of more than two on powder diffractometers.
S. T. Crites - One of the best experts on this subject based on the ideXlab platform.
-
Revised mineral and Mg# maps of the Moon from integrating results from the Lunar Prospector Neutron and gamma-ray Spectrometers with Clementine spectroscopy
American Mineralogist, 2015Co-Authors: S. T. Crites, Paul G. LuceyAbstract:Mineralogical measurements from spectral remote sensing and remote geochemical measurements from gamma-ray and Neutron Spectrometers are complementary data sets that have been used together successfully to study the distributions of iron, titanium, and rare earth elements on the Moon. We compare Neutron and gamma-ray data sets from Lunar Prospector and find them in good agreement with each other within the errors of previously developed equations that relate Neutron flux with geochemistry, but find small adjustments to the nominal values are warranted. We used the Neutron-validated LP GRS oxides to improve Clementine-based global mineral maps. The comparison was enabled by converting the minerals of Lucey (2004) to oxides using stoichiometry and assumptions about Mg#, calcium content of clinopyroxenes, and An#. We find that FeO and Al 2 O 3 derived from the maps of Lucey (2004) do not follow the expected negative correlation seen in lunar samples, but can be brought into agreement with samples and with LP GRS oxides by increasing plagioclase in proportion with orthopyroxene abundance, while simultaneously decreasing Mg#. We interpreted this to mean that plagioclase and orthopyroxene exist in rocks together (as in a noritic rock) with the spectrally difficult to detect plagioclase being masked by the strong spectral signature of the orthopyroxene. We generated a revised set of maps of the major lunar minerals and a map of Mg# for the mafic minerals that are consistent with Lunar Prospector Neutron and gamma-ray spectrometer results and show greatly improved agreement with lunar soil samples over previous global mineral maps from Clementine.
-
revised mineral and mg maps of the moon from integrating results from the lunar prospector Neutron and gamma ray Spectrometers with clementine spectroscopy
American Mineralogist, 2015Co-Authors: S. T. Crites, Paul G. LuceyAbstract:Mineralogical measurements from spectral remote sensing and remote geochemical measurements from gamma-ray and Neutron Spectrometers are complementary data sets that have been used together successfully to study the distributions of iron, titanium, and rare earth elements on the Moon. We compare Neutron and gamma-ray data sets from Lunar Prospector and find them in good agreement with each other within the errors of previously developed equations that relate Neutron flux with geochemistry, but find small adjustments to the nominal values are warranted. We used the Neutron-validated LP GRS oxides to improve Clementine-based global mineral maps. The comparison was enabled by converting the minerals of Lucey (2004) to oxides using stoichiometry and assumptions about Mg#, calcium content of clinopyroxenes, and An#. We find that FeO and Al 2 O 3 derived from the maps of Lucey (2004) do not follow the expected negative correlation seen in lunar samples, but can be brought into agreement with samples and with LP GRS oxides by increasing plagioclase in proportion with orthopyroxene abundance, while simultaneously decreasing Mg#. We interpreted this to mean that plagioclase and orthopyroxene exist in rocks together (as in a noritic rock) with the spectrally difficult to detect plagioclase being masked by the strong spectral signature of the orthopyroxene. We generated a revised set of maps of the major lunar minerals and a map of Mg# for the mafic minerals that are consistent with Lunar Prospector Neutron and gamma-ray spectrometer results and show greatly improved agreement with lunar soil samples over previous global mineral maps from Clementine.
Alan B. Binder - One of the best experts on this subject based on the ideXlab platform.
-
iron abundances on the lunar surface as measured by the lunar prospector gamma ray and Neutron Spectrometers
Journal of Geophysical Research, 2002Co-Authors: David J. Lawrence, Sylvestre Maurice, W. C. Feldman, Paul G. Lucey, Thomas H. Prettyman, R. C. Elphic, R. C. Little, Alan B. BinderAbstract:[i] Global measurements of iron abundances on the lunar surface are presented using data from the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) and Neutron Spectrometer (NS). In this study, we derive relative iron abundances from the low-altitude, high spatial resolution (∼(45 km) 2 ) LP data using the 7.6 MeV Neutron capture gamma-ray doublet. As part of the LP-GRS analysis, we demonstrate the importance of accounting for variations in Neutron number density across the lunar surface by measuring Neutron fluxes using LP-NS data. In a first step of comparing the LP-GRS data with previously published iron abundances inferred from Clementine Spectral Reflectance (CSR) data, we show that the existing CSR FeO data are nonlinear with respect to the LP relative iron abundances. We use the LP data to linearize the relationship between the CSR and the relative iron values then recalibrate the CSR data to iron abundance using returned soil abundances. We then correlate the CSR data, except for major anomalies, with the LP relative iron measurements to convert the LP data to absolute iron abundances. When we compare the LP-GRS and revised CSR data sets, we find a very good correspondence. There are two locations (Mare Tranquillitatis and South Pole-Aitken (SPA) basin) that show major discrepancies, suggesting that the CSR data are locally overestimating iron abundances. In both these regions, the discrepancies identified by the LP-GRS/CSR comparison are possibly explained by mineralogical differences that are not accounted for in the CSR to FeO calibration. In regards to our understanding of the Moon, the LP data have found the following: (I) There exist large expanses of mare basalt in the western mare regions that have very high iron abundances (22-23 wt.% FeO) that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils, which typically contain a significant amount of highlands contamination. (2) The low iron abundances in the lunar highlands (∼5 FeO wt.%) are consistent with a previous analysis using thermal and epithermal Neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process. (3) The comparison of LP and CSR derived iron abundances suggests that the material within SPA basin is similar to a norite-type rock without an enriched mantle FeO signature. (4) A comparison of LP and CSR data at Tycho Crater shows a large discrepancy such that the CSR data show moderate iron abundances of 8-9 wt.% FeO while the LP data show very low iron abundances of 3-4 wt.% FeO. This discrepancy cannot yet be easily explained by any known process.
-
Iron abundances on the lunar surface as measured by the Lunar Prospector gamma‐ray and Neutron Spectrometers
Journal of Geophysical Research, 2002Co-Authors: David J. Lawrence, Sylvestre Maurice, W. C. Feldman, Paul G. Lucey, Thomas H. Prettyman, R. C. Elphic, R. C. Little, Alan B. BinderAbstract:[i] Global measurements of iron abundances on the lunar surface are presented using data from the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) and Neutron Spectrometer (NS). In this study, we derive relative iron abundances from the low-altitude, high spatial resolution (∼(45 km) 2 ) LP data using the 7.6 MeV Neutron capture gamma-ray doublet. As part of the LP-GRS analysis, we demonstrate the importance of accounting for variations in Neutron number density across the lunar surface by measuring Neutron fluxes using LP-NS data. In a first step of comparing the LP-GRS data with previously published iron abundances inferred from Clementine Spectral Reflectance (CSR) data, we show that the existing CSR FeO data are nonlinear with respect to the LP relative iron abundances. We use the LP data to linearize the relationship between the CSR and the relative iron values then recalibrate the CSR data to iron abundance using returned soil abundances. We then correlate the CSR data, except for major anomalies, with the LP relative iron measurements to convert the LP data to absolute iron abundances. When we compare the LP-GRS and revised CSR data sets, we find a very good correspondence. There are two locations (Mare Tranquillitatis and South Pole-Aitken (SPA) basin) that show major discrepancies, suggesting that the CSR data are locally overestimating iron abundances. In both these regions, the discrepancies identified by the LP-GRS/CSR comparison are possibly explained by mineralogical differences that are not accounted for in the CSR to FeO calibration. In regards to our understanding of the Moon, the LP data have found the following: (I) There exist large expanses of mare basalt in the western mare regions that have very high iron abundances (22-23 wt.% FeO) that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils, which typically contain a significant amount of highlands contamination. (2) The low iron abundances in the lunar highlands (∼5 FeO wt.%) are consistent with a previous analysis using thermal and epithermal Neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process. (3) The comparison of LP and CSR derived iron abundances suggests that the material within SPA basin is similar to a norite-type rock without an enriched mantle FeO signature. (4) A comparison of LP and CSR data at Tycho Crater shows a large discrepancy such that the CSR data show moderate iron abundances of 8-9 wt.% FeO while the LP data show very low iron abundances of 3-4 wt.% FeO. This discrepancy cannot yet be easily explained by any known process.
-
THE LUNAR PROSPECTOR GAMMA-RAY AND Neutron Spectrometers
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 1999Co-Authors: W. C. Feldman, David J. Lawrence, Sylvestre Maurice, B. L. Barraclough, Thomas H. Prettyman, K. R. Fuller, M.c. Miller, Alan B. BinderAbstract:Gamma-ray and Neutron Spectrometers (GRS and NS, respectively) are included in the payload complement of Lunar Prospector (LP) that is currently orbiting the Moon. Specific objectives of the GRS are to map abundances of O, Si, Fe, Ti, U, Th, K, and perhaps, Mg, Al, and Ca, to depths of about 20 cm. Those of the NS are to search for water ice to depths of about 50 cm near the lunar poles and to map regolith maturity. The designs of both Spectrometers are described and their performance in both the laboratory and in lunar orbit are presented. ( 1999 Elsevier Science B.V. All rights reserved.