Instrument Calibrations and Data Analysis Procedures for the NEAR X-Ray Spectrometer
TL;DR: The 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 as discussed by the authors.
About: This article is published in Icarus.The article was published on 2000-10-01. It has received 28 citations till now. The article focuses on the topics: Spectrometer.
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TL;DR: In this paper, the major element ratios determined for the S-class asteroid 433 Eros using remote-sensing x-ray fluorescence spectroscopy with the near-Earth asteroid rendezvous Shoemaker X-ray spectrometer (XRS).
Abstract: We report major element ratios determined for the S-class asteroid 433 Eros using remote- sensing x-ray fluorescence spectroscopy with the near-Earth asteroid rendezvous Shoemaker x-ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended "quiet Sun" periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact-induced volatilization and/or photo- or ion-induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS-rich partial melt. Size-sorting processes could lead to segregation of Fe-Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x-ray spectrometer are not representative of the bulk Eros composition.
122 citations
TL;DR: The MErcury, Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission as discussed by the authors is the first spacecraft to orbit the planet Mercury.
119 citations
TL;DR: The 3.8-10 keV solar flare spectrum includes lines of highly stripped Ca, Fe, and Ni ions, as well as a continuum steeply falling with energy.
Abstract: The 3.8–10 keV solar flare spectrum includes lines of highly stripped Ca, Fe, and Ni ions, as well as a continuum steeply falling with energy. Groups of lines at � 7a nd� 8 keV, observed during flares by the broadband RHESSI spectrometer and called here the Fe line and Fe/Ni line features, are formed mostly of Fe lines but with Ni lines contributing to the � 8 keV feature. Possible temperature indicators of these line features are discussed: the peak or centroid energies of the Fe line feature, the line ratio of the Fe line to the Fe/Ni line features, and the equivalent width of the Fe line feature. The equivalent width is by far the most sensitive to temperature. However, results will be confused if, as is commonly believed, the abundance of Fe varies from flare to flare, even during the course of a single flare. With temperature determined from the thermal continuum, the Fe line feature becomes a diagnostic of the Fe abundance in flare plasmas. These results are of interest for other hot plasmas in coronal ionization equilibrium such as stellar flare plasmas, hot gas in galaxies, and older supernova remnants.
91 citations
Cites methods from "Instrument Calibrations and Data An..."
...…(FWHM ¼ 0:2 0:8 keV) were obtained by the Soft X-Ray Spectrometer part of the Wide Band Spectrometer on Yohkoh (Yoshimori et al. 1991) and the solid-state PIN detector, part of the X-Ray/Gamma-Ray Spectrometer (XGRS) aboard the Near Earth Asteroid Rendezvous (NEAR) mission (Starr et al. 2000)....
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TL;DR: In this paper, the authors present measurements of Mercury's surface composition from the analysis of MESSENGER X-Ray Spectrometer data acquired during 55 large solar flares, which each provide a statistically significant detection of Fe X-ray fluorescence.
72 citations
01 Mar 2002
TL;DR: Based on solar fluorescence X-ray spectra obtained from orbit, the abundance of major rock-forming elements at Eros may be consistent with that of ordinary chondrite meteorites except for a depletion in S as discussed by the authors.
Abstract: On February 14, 2000, the Near Earth Asteroid Rendezvous spacecraft (NEAR Shoemaker) began the first orbital study of an asteroid, the near-Earth object 433 Eros. Almost a year later, on February 12, 2001, NEAR Shoemaker completed its mission by landing on the asteroid and acquiring data from its surface. NEAR Shoemaker’s intensive study has found an average density of 2.67 ± 0.03, almost uniform within the asteroid. Based upon solar fluorescence X-ray spectra obtained from orbit, the abundance of major rock-forming elements at Eros may be consistent with that of ordinary chondrite meteorites except for a depletion in S. Such a composition would be consistent with spatially resolved, visible and near-infrared (NIR) spectra of the surface. Gamma-ray spectra from the surface show Fe to be depleted from chondritic values, but not K. Eros is not a highly differentiated body, but some degree of partial melting or differentiation cannot be ruled out. No evidence has been found for compositional heterogeneity or an intrinsic magnetic field. The surface is covered by a regolith estimated at tens of meters thick, formed by successive impacts. Some areas have lesser surface age and were apparently more recently disturbed or covered by regolith. A small center of mass offset from the center of figure suggests regionally nonuniform regolith thickness or internal density variation. Blocks have a nonuniform distribution consistent with emplacement of ejecta from the youngest large crater. Some topographic features indicate tectonic deformations. Several regional-scale linear features have related orientations, suggesting a globally consolidated internal structure. Structural control of crater shapes hints that such internal structure is pervasive. From the bulk density, inferred composition, and evidence for global structure, Eros is interpreted to be largely intact but extensively fractured.
68 citations
Cites background from "Instrument Calibrations and Data An..."
...X-Ray Spectrometer (XRS) The XRS (Goldsten et al., 1997; Starr et al., 2000) was an X-ray fluorescence spectrometer that measured characteristic X-ray line emissions excited by solar X-rays from major elements in the asteroid’s surface....
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...The XRS is sensitive to element ratios only within the uppermost few tens of microns depth, and it is not clear whether the S depletion is a surface effect due to impact devolatilization or a bulk Eros phenomenon that suggests removal of partial melt at the time Eros was part of its parent body....
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...The NEAR XRS/GRS experiment, even in its low-altitude orbits, observed both X-ray and γ-ray signal levels that were lower than predicted prelaunch....
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...In orbits at 50 km or lower, the highest-priority science was compositional measurement by XRS/GRS....
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...The XRS did not find any evidence for spatial heterogeneity in composition....
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References
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Book•
01 Jan 1979
TL;DR: In this paper, the authors present a detailed analysis of the effect of different types of detectors on the performance of the detection of neutrons and their effect on the detection efficiency and error prediction.
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.
8,458 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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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.
95 citations
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.
57 citations
TL;DR: In this article, the authors discuss the nature of such variations expected for missions to an asteroid, the Moon, and Mercury, and discuss 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.
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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TL;DR: The X ray/gamma ray spectrometer (XGRS) instrument on board the NEAR spacecraft will map asteroid 433 Eros in the 07 keV to 10 MeV energy region as discussed by the authors.
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