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Journal ArticleDOI

Instrument Calibrations and Data Analysis Procedures for the NEAR X-Ray Spectrometer

01 Oct 2000-Icarus (Academic Press)-Vol. 147, Iss: 2, pp 498-519

AbstractThe X-Ray spectrometer onboard the Near Earth Asteroid Rendezvous spacecraft will measure X-rays from the surface of 433 Eros in the energy region 0.7–10 keV. Detection of characteristic Kα line emissions from Mg, Al, Si, Ca, Ti, and Fe will allow the determination of surface abundances of these geologically important elements. Spatial resolution as fine as 3 km will be possible for those elements where counting statistics are not a limiting factor. These measurements will make it possible to relate Eros to known classes of meteorites and reveal geological processes that occurred on Eros. The calibration measurements and analysis procedures presented here are necessary for the reduction and analysis of the X-ray data to be collected during one year of orbital operations at Eros.

Topics: Spectrometer (53%)

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Journal ArticleDOI
Abstract: [1] We present the analysis of 205 spatially resolved measurements of the surface composition of Mercury from MESSENGER’s X-Ray Spectrometer. The surface footprints of these measurements are categorized according to geological terrain. Northern smooth plains deposits and the plains interior to the Caloris basin differ compositionally from older terrain on Mercury. The older terrain generally has higher Mg/Si, S/Si, and Ca/Si ratios, and a lower Al/Si ratio than the smooth plains. Mercury’s surface mineralogy is likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, and lesser amounts of Ca, Mg, and/or Fe sulfides (e.g., oldhamite). The compositional difference between the volcanic smooth plains and the older terrain reflects different abundances of these minerals and points to the crystallization of the smooth plains from a more chemically evolved magma source. High-degree partial melts of enstatite chondrite material provide a generally good compositional and mineralogical match for much of the surface of Mercury. An exception is Fe, for which the low surface abundance on Mercury is still higher than that of melts from enstatite chondrites and may indicate an exogenous contribution from meteoroid impacts.

166 citations


01 Sep 2012
Abstract: [1] We present the analysis of 205 spatially resolved measurements of the surface composition of Mercury from MESSENGER’s X-Ray Spectrometer. The surface footprints of these measurements are categorized according to geological terrain. Northern smooth plains deposits and the plains interior to the Caloris basin differ compositionally from older terrain on Mercury. The older terrain generally has higher Mg/Si, S/Si, and Ca/Si ratios, and a lower Al/Si ratio than the smooth plains. Mercury’s surface mineralogy is likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, and lesser amounts of Ca, Mg, and/or Fe sulfides (e.g., oldhamite). The compositional difference between the volcanic smooth plains and the older terrain reflects different abundances of these minerals and points to the crystallization of the smooth plains from a more chemically evolved magma source. High-degree partial melts of enstatite chondrite material provide a generally good compositional and mineralogical match for much of the surface of Mercury. An exception is Fe, for which the low surface abundance on Mercury is still higher than that of melts from enstatite chondrites and may indicate an exogenous contribution from meteoroid impacts.

148 citations


Journal ArticleDOI
Abstract: During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at energies below 2 keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies. At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1–2 keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles. This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun. Processes of production of solar system X-rays are discussed and an overview is provided of the main source mechanisms of X-ray production at each object. A brief account on recent development in the area of laboratory studies of X-ray production is also provided.

138 citations


Journal ArticleDOI
Abstract: NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12° field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes XRS’s science objectives, technical design, calibration, and mission observation strategy.

124 citations


Cites background from "Instrument Calibrations and Data An..."

  • ...The XRS instrument owes much of its heritage to the X-ray/gamma-ray spectrometer (XGRS) instrument on the Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission (Starr et al. 2000)....

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Journal ArticleDOI
Abstract: We have mapped the major-element composition of Mercury's surface from orbital MESSENGER X-Ray Spectrometer measurements. These maps constitute the first global-scale survey of the surface composition of a Solar System body conducted with the technique of planetary X-ray fluorescence. Full maps of Mg and Al, together with partial maps of S, Ca, and Fe, each relative to Si, reveal highly variable compositions (e.g., Mg/Si and Al/Si range over 0.1–0.8 and 0.1–0.4, respectively). The geochemical variations that we observe are consistent with those inferred from other MESSENGER geochemical remote sensing datasets, but they do not correlate well with units mapped previously from spectral reflectance or morphology. Location-dependent, rather than temporally evolving, partial melt sources were likely the major influence on the compositions of the magmas that produced different geochemical terranes. A large ( > 5 × 10 6 km 2 ) region with the highest Mg/Si, Ca/Si, and S/Si ratios, as well as relatively thin crust, may be the site of an ancient and heavily degraded impact basin. The distinctive geochemical signature of this region could be the consequence of high-degree partial melting of a reservoir in a vertically heterogeneous mantle that was sampled primarily as a result of the impact event.

124 citations


Cites methods from "Instrument Calibrations and Data An..."

  • ...A “balanced filter” approach (Starr et al., 2000) was therefore employed, in which thin foils of Mg and Al placed in front of two GPCs provide selective absorption at different energies and allow the fluorescent signals from these elements to be deconvolved (Adler et al., 1972; Trombka et al.,…...

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References
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Book
01 Jan 1979
Abstract: Chapter 1 Radiation Sources. I. Units And Definitions. II. Fast Electron Sources. III. Heavy Charged Particle Sources. IV. Sources Of Electromagnetic Radiation. V. Neutron Sources. Chapter 2 Radiation Interactions. I. Interaction Of Heavy Charged Particles. II. Interaction Of Fast Electrons. III. Interaction Of Gamma Rays. IV. Interaction Of Neutrons. V. Radiation Exposure And Dose. Chapter 3 Counting Statistics And Error Prediction. I. Characterization Of Data. II. Statistical Models. III. Applications Of Statistical Models. IV. Error Propagation. V. Optimization Of Counting Experiments. VI. Limits Of Detectability. VII. Distribution Of Time Intervals. Chapter 4 General Properties Of Radiation Detectors. I. Simplified Detector Model. II. Modes Of Detector Operation. III. Pulse Height Spectra. IV. Counting Curves And Plateaus. V. Energy Resolution. VI. Detection Efficiency. VII. Dead Time. Chapter 5 Ionization Chambers. I. The Ionization Process In Gases. II. Charge Migration And Collection. III. Design And Operation Of Dc Ion Chambers. IV. Radiation Dose Measurement With Ion Chambers. V. Applications Of Dc Ion Chambers. VI. Pulse Mode Operation. Chapter 6 Proportional Counters. I. Gas Multiplication. II. Design Features Of Proportional Counters. III. Proportional Counter Performance. IV. Detection Efficiency And Counting Curves. V. Variants Of The Proportional Counter Design. VI. Micropattern Gas Detectors. Chapter 7 Geiger-Mueller Counters. I. The Geiger Discharge. II. Fill Gases. III. Quenching. IV. Time Behavior. V. The Geiger Counting Plateau. VI. Design Features. VII. Counting Efficiency. VIII. Time-To-First-Count Method. IX. G-M Survey Meters. Chapter 8 Scintillation Detector Principles. I. Organic Scintillators. II. Inorganic Scintillators. III. Light Collection And Scintillator Mounting. Chapter 9 Photomultiplier Tubes And Photodiodes. I. Introduction. II. The Photocathode. III. Electron Multiplication. IV. Photomultiplier Tube Characteristics. V. Ancillary Equipment Required With Photomultiplier Tubes. VI. Photodiodes As Substitutes For Photomultiplier Tubes. VII. Scintillation Pulse Shape Analysis. VIII. Hybrid Photomultiplier Tubes. IX. Position-Sensing Photomultiplier Tubes. X. Photoionization Detectors. Chapter 10 Radiation Spectroscopy With Scintillators. I. General Considerations In Gamma-Ray Spectroscopy. II. Gamma-Ray Interactions. III. Predicted Response Functions. IV. Properties Of Scintillation Gamma-Ray Spectrometers. V. Response Of Scintillation Detectors To Neutrons. VI. Electron Spectroscopy With Scintillators. VII. Specialized Detector Configurations Based On Scintillation. Chapter 11 Semiconductor Diode Detectors. I. Semiconductor Properties. II. The Action Of Ionizing Radiation In Semiconductors. III. Semiconductors As Radiation Detectors. IV. Semiconductor Detector Configurations. V. Operational Characteristics. VI. Applications Of Silicon Diode Detectors. Chapter 12 Germanium Gamma-Ray Detectors. I. General Considerations. II. Configurations Of Germanium Detectors. III. Germanium Detector Operational Characteristics. IV. Gamma-Ray Spectroscopy With Germanium Detectors. Chapter 13 Other Solid-State Detectors. I. Lithium-Drifted Silicon Detectors. II. Semiconductor Materials Other Than Silicon Or Germanium. III. Avalanche Detectors. IV. Photoconductive Detectors. V. Position-Sensitive Semiconductor Detectors. Chapter 14 Slow Neutron Detection Methods. I. Nuclear Reactions Of Interest In Neutron Detection. II. Detectors Based On The Boron Reaction. III. Detectors Based On Other Conversion Reactions. IV. Reactor Instrumentation. Chapter 15 Fast Neutron Detection And Spectroscopy. I. Counters Based On Neutron Moderation. II. Detectors Based On Fast Neutron-Induced Reactions. III. Detectors That Utilize Fast Neutron Scattering. Chapter 16 Pulse Processing. I. Overview Of Pulse Processing. II. Device Impedances. III. Coaxial Cables. IV. Linear And Logic Pulses. V. Instrument Standards. VI. Summary Of Pulse-Processing Units. VII. Application Specific Integrated Circuits (ASICS). VIII. Components Common To Many Applications. Chapter 17 Pulse Shaping, Counting, And Timing. I. Pulse Shaping. II. Pulse Counting Systems. III. Pulse Height Analysis Systems. IV. Digital Pulse Processing. V. Systems Involving Pulse Timing. VI. Pulse Shape Discrimination. Chapter 18 Multichannel Pulse Analysis. I. Single-Channel Methods. II. General Multichannel Characteristics. III. The Multichannel Analyzer. IV. Spectrum Stabilization And Relocation. V. Spectrum Analysis. Chapter 19 Miscellaneous Detector Types. I. Cherenkov Detectors. II. Gas-Filled Detectors In Self-Quenched Streamer Mode. III. High-Pressure Xenon Spectrometers. IV. Liquid Ionization And Proportional Counters. V. Cryogenic Detectors. VI. Photographic Emulsions. VII. Thermoluminescent Dosimeters And Image Plates. VIII. Track-Etch Detectors. IX. Superheated Drop Or "Bubble Detectors". X. Neutron Detection By Activation. XI. Detection Methods Based On Integrated Circuit Components. Chapter 20 Background And Detector Shielding. I. Sources Of Background. II. Background In Gamma-Ray Spectra. III. Background In Other Detectors. IV. Shielding Materials. V. Active Methods Of Background Reduction. Appendix A The NIM, CAMAC, And VME Instrumentation Standards. Appendix B Derivation Of The Expression For Sample Variance In Chapter 3. Appendix C Statistical Behavior Of Counting Data For Variable Mean Value. Appendix D The Shockley-Ramo Theorem For Induced Charge.

8,453 citations


"Instrument Calibrations and Data An..." refers background in this paper

  • ...A detailed description of the response of proportional counters can be found in Knoll (1989). The gas proportional counters on NEAR have a chamber diameter of 42 mm and are filled with P-10 gas, a mixture of 90% argon and 10% methane, to an absolute pressure of 1200 mbar....

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  • ...A detailed description of the response of proportional counters can be found in Knoll (1989)....

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  • ...(See, for example, Knoll, 1989)....

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Journal ArticleDOI
28 Jan 1972-Science
TL;DR: The results indicate the existence of a differential lunar highland crust, probably feldspathic, related to the plagioclase-rich materials previously found in the samples from Apollo 11, Apollo 12, Apollo 14, Apollo 15, and Luna 16.
Abstract: Although only part of the information from the x-ray fluorescence geochemical experiment has been analyzed, it is clear that the experiment was highly successful. Significant compositional differences among and possibly within the maria and highlands have been detected. When viewed in the light of analyzed lunar rocks and soil samples, and the data from other lunar orbital experiments (in particular, the Apollo 15 gamma-ray spectroscopy experiment), the results indicate the existence of a differential lunar highland crust, probably feldspathic. This crust appears to be related to the plagioclase-rich materials previously found in the samples from Apollo 11, Apollo 12, Apollo 14, Apollo 15, and Luna 16.

93 citations


Journal ArticleDOI
Abstract: Remote X-ray spectrometry will play a key role in the geochemical exploration of solar system bodies, provided the methodology for data analysis efficiently detects and removes solar source and flight trajectory-induced geometric variations. In this paper, we discuss the nature of such variations expected for missions to an asteroid, the Moon, and Mercury. An effective means of removing the effects of solar variability from surface measurements, as indicated by the agreement between theoretical models presented here and Apollo X-ray observations, is also discussed. We calculate X-ray spectra anticipated for these targets using probable surface compositions, solar outputs, and flight trajectories. Generally, the spectra show three distinctive regions where line intensities are clearly correlated with surface abundances: a high-energy Fe region, a moderate-energy Ca region, and a low-energy region which contains Mg, Al, and Si lines. In addition, we calculate anticipated integration times required for acceptable levels of certainty and estimate spatial resolutions achievable for those integration times for elements Mg, Al, Si, S, Ca, Ti, and Fe. Required integration times are lower (on the order of minutes or even seconds) and achievable spatial resolutions improved (on the order of kilometers) for the lower energy lines and for periods of higher solar activity. Using the Near Earth Asteroid Rendezvous (NEAR) mission to asteroid 433 Eros as an example, we describe a recommended approach for analysis of X-ray measurements based on our findings. Most importantly, we clearly demonstrate that major scientific goals for future exploration of asteroids, Mercury, and the Moon can be met by obtaining remote orbital X-ray measurements of these bodies.

56 citations


"Instrument Calibrations and Data An..." refers background or methods in this paper

  • ...LIBRATION 509 Detailed discussions of these processes can be found in Clark (1979), Trombka et al. (1979), Yin et al. (1993), and Clark and Trombka (1997)....

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  • ...Laboratory and field calibrations, in conjunction with theoretical calculations, are required in order to obtain photon-to-elemental composition conversion factors. eter data is described in Clark (1979) and Clark and Trombka (1997)....

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Journal ArticleDOI
21 Jul 1972-Science
TL;DR: The lunar surface was mapped with respect to magnesium, aluminum, and silicon as aluminum/ silicon and magnesium/ silicon intensity ratios along the projected ground tracks swept out by the orbiting Apollo 16 spacecraft to confirm the idea that the moon has a widespread differentiated crust (the highlands).
Abstract: The lunar surface was mapped with respect to magnesium, aluminum, and silicon as aluminum/ silicon and magnesium/ silicon intensity ratios along the projected ground tracks swept out by the orbiting Apollo 16 spacecraft. The results confirm the observations made during the Apollo 15 flight and provide new data for a number of features not covered before. The data are consistent with the idea that the moon has a widespread differentiated crust (the highlands). The aluminum/ silicon and magnesium/ silicon concentration ratios correspond to those for anorthositic gabbros through gabbroic anorthosites or feldspathic basalts. The x-ray results suggest the occurrence of this premare crust or material similar to it at the Descartes landing site.

56 citations


Journal ArticleDOI
Abstract: The X ray/gamma ray spectrometer (XGRS) instrument on board the Near Earth Asteroid Rendezvous (NEAR) spacecraft will map asteroid 433 Eros in the 07 keV to 10 MeV energy region Measurements of the discrete line X ray and gamma ray emissions in this energy domain can be used to obtain both qualitative and quantitative elemental compositions with sufficient accuracy to enable comparison to the major meteorite typies It is believed that Eros is an S-type asteroid, the most common of the near-Earth asteroids The determination of whether Eros consists of either differentiated or undifferentiated materials is an important objective of this mission Observations of Eros during the NEAR mission will contribute significantly to our understanding of the structure and composition of this asteroid The NEAR spacecraft was successfully launched on February 17, 1996 The NEAR XGRS was turned on during the week of April 7, 1996, and all detector systems operated nominally Background spectra have been obtained

54 citations


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