PDS_VERSION_ID               = PDS3
LABEL_REVISION_NOTE          = "
         2007-08-01 MESS:mick   V01 First Draft / Example;
         2007-08-10 MESS:chabot V02 Added Content;
         2007-12-11 GEO:slavney Separated GRS and NS;
         2009-08-07 GEO:ward    Edits from CDR peer review."

RECORD_TYPE                       = STREAM

OBJECT                         = INSTRUMENT
  INSTRUMENT_HOST_ID             = "MESS"
  INSTRUMENT_ID                  = "NS"

  OBJECT                         = INSTRUMENT_INFORMATION
   INSTRUMENT_NAME                = "NEUTRON SPECTROMETER"
   INSTRUMENT_TYPE                = "NEUTRON SPECTROMETER"
   INSTRUMENT_DESC                = "

   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 NS sensor consists of three scintillators, each wrapped 
   separately and coupled to separate photo-multiplier tubes. The 
   three scintillators are sensitive to neutrons of different 
   energies: thermal neutrons (0.025 - 1 eV), epithermal neutrons 
   (1 eV - 500 keV), and fast neutrons (500 keV - 7 MeV). The first 
   and third scintillators are lithium (6Li)-glass scintillators (LG1 
   and LG2) which respond to a combination of thermal and epithermal 
   neutrons. The middle scintillator is a borated plastic (BP) 
   scintillator that responds only to epithermal and fast neutrons due 
   to its electronics setup. The interaction of galactic cosmic rays 
   (GCR) with the surface of Mercury produces neutrons, some of which 
   escape the surface and produce a neutron signal that can be 
   measured by the orbiting NS sensor. The measured neutron energy 
   spectrum reflects the transport properties of the surface 
   composition and is sensitive to depths down to about 1 m. Thermal 
   neutrons are sensitive to a variety of elements, including Fe, Ti, 
   Gd, Sm, Cl, and C. Epithermal neutrons are mostly sensitive to H 
   abundance. Fast neutrons can provide a good measure of average 
   atomic mass. For the MESSENGER mission, the NS sensor will 
   establish and map the abundance of H over most of the northern 
   hemisphere of Mercury, providing significant new information 
   regarding the potential presence of water ice within and near 
   permanently shaded craters near the north pole.

   The GRS detector is described in the catalog file GRS_INST.CAT in 
   the GRS archive. Both instruments are described in full detail in
   [GOLDSTENETAL2007]."

  END_OBJECT                     = INSTRUMENT_INFORMATION

  OBJECT                         = INSTRUMENT_REFERENCE_INFO
    REFERENCE_KEY_ID             = "GOLDSTENETAL2007"
  END_OBJECT                     = INSTRUMENT_REFERENCE_INFO

END_OBJECT                     = INSTRUMENT
END