urn:nasa:pds:context:instrument:grs.mess 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.mess::1.0 instrument_to_instrument_host Goldsten, J.O., E.A. Rhodes,, W.V. Boynton, W.C. Feldman, D.J. Lawrence, J.I. Trombka, D.M. Smith, L.G. Evans, J. White, N.W. Madden, P.C. Berg, G.A. Murphy, R.S. Gurnee, K. Strohbehn, B.D. Williams, E.D. Schaefer, C.A. Monaco, C.P. Cork, J.D. Eckels, W.O. Miller, M.T. Burks, L.B. Hagler, S.J. Deteresa, and M.C. Witte, The MESSENGER Gamma-Ray and Neutron Spectrometer, Space Science Reviews, 131, 339-391, 2007. reference.GOLDSTENETAL2007 GAMMA RAY SPECTROMETER Spectrometer not applicable not applicable The Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission is designed to orbit Mercury following one Earth flyby, two flybys of Venus and three of Mercury. It launched in August 2004 and will use these flybys to achieve an orbit insertion around Mercury in March 2011. Initial data collection will begin during the three flybys of Mercury, and will primarily consist of global mapping and measurements of the surface, atmosphere and magnetosphere composition. MESSENGER will remain in orbit for the rest of the nominal mission, which is scheduled to end in March 2012. Once in orbit around Mercury it will begin a series of observations using multiple instruments. These observations will provide data to answer questions about the nature and composition of Mercury's crust, tectonic history, the structure of the atmosphere and magnetosphere, and the nature of the polar deposits. The Gamma-Ray and Neutron Spectrometer (GRNS) instrument forms part of the geochemistry investigation of the MESSENGER mission and will yield information about the elemental composition of the planet's surface. The GRNS package is composed of two independent sensors: the Gamma-Ray Spectrometer (GRS) and the Neutron Spectrometer (NS). GRS detects gamma-ray emissions in the 0.1 - 10 MeV range, allowing the identification of certain elements and their abundances to be determined. NS measures the flux of ejected neutrons in three energy ranges and is particularly sensitive to the H content of a body. Taken together, the gamma-ray and neutron measurements will be used to infer the composition of Mercury's surface over localized regions using established techniques, such as used recently on the Lunar Prospector and Mars Odyssey missions. The GRS detector is a coaxial germanium crystal 50 mm in diameter and 50 mm in length, chosen for its superior energy resolution and the ability to anneal the detector to remove accumulated radiation damage. The detector is rigidly clamped in a hermetically sealed Al capsule pressurized with clean, dry nitrogen. The capsule is cooled to an operating temperature in the 80-95 K range by a mechanical cryocooler. A plastic scintillator anti-coincidence shield surrounds the germanium detector in its sides and back, for rejection of cosmic-ray background. Galactic cosmic rays continuously bombard the surface of Mercury, and through interactions with the surface, gamma rays of discrete energies that are characteristic of specific elements are created. A fraction of these gamma rays, as well as those from the decay of radiogenic elements escape from the surface, where they can be detected by the orbiting GRS. Gamma-ray fluxes are measurable at altitudes up to 1000 km and for gamma rays up to about 10 MeV that emanate from depths of up to tens of centimeter beneath the surface. Detected fluxes are generally low and require numerous orbital passes over a specific region to obtain a statistically well-defined energy spectrum. The measurements of elements such as Fe, Si, Mg, Na, Al, Ca, Ti, K and Th by GRS will provide insight into distinguishing between different formation models for Mercury as well as other planetary evolution issues. The NS detector is described in the catalog file NS_INST.CAT in the NS archive. Both instruments are described in full detail in [GOLDSTENETAL2007].