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boom, which was extended after
Odyssey entered the mapping orbit at Mars. This maneuver is done to minimize interference from any gamma rays coming from the spacecraft itself. The initial spectrometer activity, lasting between 15 and 40 days, performed an instrument calibration before the boom was deployed. After about 100 days of the mapping mission, the boom was deployed and remained in this position for the duration of the mission. The two neutron detectors-the neutron spectrometer and the high-energy neutron detector-are mounted on the main spacecraft structure and operated continuously throughout the mapping mission.
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soil. The GRS measured their energies. Certain energies are produced by hydrogen. Since hydrogen is most likely present in the form of water ice, the spectrometer will be able to measure directly the amount of permanent ground ice and how it changes with the seasons. Like a virtual shovel "digging into" the surface, the spectrometer will allow scientists to peer into this shallow subsurface of Mars and measure the existence of hydrogen.
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The Gamma-Ray
Spectrometer weighs 30.5 kilograms (67.2 lb) and uses 32 watts of power. Along with its cooler, it measures 468 by 534 by 604 mm (18.4 by 21.0 by 23.8 in). The detector is a photodiode made of a 1.2 kg germanium crystal, reverse biased to about 3 kilovolts, mounted at the
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The gamma-ray spectrometer used on the
Odyssey spacecraft consists of four main components: the gamma sensor head, the neutron spectrometer, the high energy neutron detector, and the central electronics assembly. The sensor head is separated from the rest of the spacecraft by a 6.2 meter (20 ft)
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to ~10 keV) so that the terminology used to distinguish X-rays from gamma rays can be arbitrary or ambiguous in the overlap region.) As with atoms, the particular energy levels of nuclei are characteristic of each species, so that the photon energies of the gamma rays emitted, which correspond to the
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Boynton, W.V.; Feldman, W.C.; Mitrofanov, I.G.; Evans, L.G.; Reedy, R.C.; Squyres, S.W.; Starr, R.; Trombka, J.I.; d'Uston, C.; Arnold, J.R.; Englert, P.A.J.; Metzger, A.E.; Wänke, H.; Brückner, J.; Drake, D.M.; Shinohara, C.; Fellows, C.; Hamara, D.K.; Harshman, K.; Kerry, K.; Turner, C.; Ward, M.;
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have an energy-level structure somewhat analogous to the energy levels of atoms, so that they may emit (or absorb) photons of particular energies, much as atoms do, but at energies that are thousands to millions of times higher than those typically studied in optical spectroscopy. (Note that photons
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By measuring neutrons, it is possible to calculate the abundance of hydrogen, thus inferring the presence of water. The neutron detectors are sensitive to concentrations of hydrogen in the upper meter of the surface. When cosmic rays hit the surface of Mars, neutrons and gamma-rays come out of the
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on the instrument's spectrum output. While the energy represented in these emissions determines which elements are present, the intensity of the spectrum reveals the elements concentrations. Spectrometers are expected to add significantly to the growing understanding of the origin and evolution of
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of atoms in the soil. When nuclei are hit with such energy, neutrons are released, which scatter and collide with other nuclei. The nuclei get "excited" in the process, and emit gamma rays to release the extra energy so they can return to their normal rest state. Some elements like potassium,
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energy differences of the nuclei, can be used to identify particular elements and isotopes. Distinguishing between gamma-rays of slightly different energy is an important consideration in the analysis of complex spectra, and the ability of a GRS to do so is characterized by the instrument's
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detecting elements, have been invaluable for such applications. Because the energy level spectrum of nuclei typically dies out above about 10 MeV, gamma-ray instruments looking to still higher energies generally observe only continuum spectra, so that the moderate spectral resolution of
69:, and gamma-ray spectrometers are the instruments which observe and collect such data. Because the energy of each photon of EM radiation is proportional to its frequency, gamma rays have sufficient energy that they are typically observed by counting individual photons.
225:, which excite nuclei in them to emit characteristic gamma-rays which can be detected from orbit. Thus an orbiting instrument can in principle map the surface distribution of the elements for an entire planet. Examples include the mapping of 20
366:), chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. The gamma-ray spectrometer looks at these signatures, or energies, coming from the elements present in the target soil.
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Laboratory equipment for determination of γ-radiation spectrum with a scintillation counter. The output from the scintillation counter goes to a
Multichannel Analyser which processes and formats the data.
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By measuring gamma rays coming from the target body, it is possible to calculate the abundance of various elements and how they are distributed around the planet's surface. Gamma rays, emitted from the
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The high-energy neutron detector measures 303 by 248 by 242 mm (11.9 by 9.8 by 9.5 in). The instrument's central electronics box is 281 by 243 by 234 mm (11.1 by 9.6 by 9.2 in).
566:
Barthe, H.; Fuller, K.R.; Storms, S.A.; Thornton, G.W.; Longmire, J.L.; Litvak, M.L.; Ton'Chev, A.K. (2004). "The Mars
Odyssey Gamma-Ray Spectrometer Instrument Suite".
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end of a six-meter boom to minimize interferences from the gamma radiation produced by the spacecraft itself. Its spatial resolution is about 300 km.
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GRS will supply data similar to that of the successful Lunar
Prospector mission, which told us how much hydrogen, and thus water, is likely on the Moon.
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that produces pulses proportional to the captured photon energy; while more sensitive, it has to be cooled to a low temperature, requiring a bulky
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Lawrence, D. J.; Feldman, W. C.; Barraclough, B. L.; Binder, A. B.; Elphic, R. C.; Maurice, S.; Thomsen, D. R. (1998).
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can be used as gamma-ray spectrometers. The gamma photon energy is discerned from the intensity of the flash of the
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apparatus. Handheld and many laboratory gamma spectrometers are therefore the scintillator kind, mostly with
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Gamma-ray spectrometers have been widely used for the elemental and isotopic analysis of bodies in the
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and the imaging Ge spectrometer on the RHESSI satellite have been devoted to solar observations.
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GRS instruments supply data on the distribution and abundance of chemical elements, much as the
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on GRS directly detect scattered neutrons, and the gamma sensor detects the gamma rays.
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A number of investigations have been performed to observe the gamma-ray spectra of the
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was mapped, with higher concentrations shown as yellow/orange/red in the left image.
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in the short-wavelength high-energy end of the atomic spectroscopy energy range (few
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509:"Global Elemental Maps of the Moon: The Lunar Prospector Gamma-Ray Spectrometer"
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The neutron spectrometer is 173 by 144 by 314 mm (6.8 by 5.7 by 12.4 in).
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planets like Mars and the processes shaping them today and in the past.
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Gamma rays and neutrons are produced by cosmic rays. Incoming
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mission did on the Moon. In this case, the chemical element
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NASA Jet
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are naturally radioactive and give off gamma rays as they
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that can look for water and ice in the soil by measuring
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30:For the more general field of spectroscopy, see
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617:NASA Space Science Data Coordinated Archive
455:Gamma Ray Spectrometer (2001 Mars Odyssey)
449:GRS specifications for the Odyssey mission
45:Spectrum of Co; peaks at 1.17 and 1.33 MeV
36:Gamma Ray Spectrometer (2001 Mars Odyssey)
155:, both galactic and extra-galactic. The
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72:Some notable gamma-ray spectrometers are
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34:. For the specific 2001 instrument, see
27:Instrument for measuring gamma radiation
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229:observed in the exploration of Mars,
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364:active galactic nuclei
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308:Some constructions of
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568:Space Science Reviews
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360:supernova
326:cryogenic
322:germanium
263:potassium
259:magnesium
169:germanium
167:, the C1
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683:Category
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640:Archived
554:NASA.gov
477:See also
330:thallium
267:aluminum
243:neutrons
233:and the
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180:INTEGRAL
55:spectrum
646:at the
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521:Bibcode
513:Science
408:thorium
404:uranium
399:nucleus
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271:calcium
247:silicon
203:thorium
201:map of
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100:Atomic
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173:HEAO 3
161:HEAO 1
115:X-rays
102:nuclei
80:, and
63:photon
59:figure
600:S2CID
412:decay
383:atoms
334:doped
78:AGATA
57:—see
592:ISSN
537:PMID
418:and
416:HEND
362:and
255:iron
235:Moon
231:Eros
219:Mars
217:and
215:Moon
165:CGRO
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