PDS_VERSION_ID                = PDS3
RECORD_TYPE                   = STREAM

OBJECT                        = INSTRUMENT
INSTRUMENT_HOST_ID            = LP
INSTRUMENT_ID                 = GRS

OBJECT                        = INSTRUMENT_INFORMATION
INSTRUMENT_NAME               = "GAMMA RAY SPECTROMETER"
INSTRUMENT_TYPE               = SPECTROMETER
INSTRUMENT_DESC               = "

Instrument Overview
===================

The Lunar Prospector Gamma Ray Spectrometer (GRS) sensor consists of a
7.1 cm diameter by 7.6 cm long bismuth germanate (BGO) crystal, placed
within a 12 cm diameter by 20 cm long, borated-plastic anticoincidence
shield (ACS).  Both scintillators are viewed by separate
photomultiplier tubes, and enclosed in a cylindrical, graphite-epoxy
housing.  The GRS has a mass of 8.6 kg and uses about 3 w of power
[BINDERETAL1998].
 
Science Objectives
==================

The GRS will estimate the global surface abundances of key elements
(U, Th, K, O, Si, Mg, Fe, Ti, Ca, Al, and H).  The GRS will provide
new constraints on the bulk composition of the crust, on compositional
variations over the lunar surface, and on the existence of lunar
resources.  The GRS will investigate how large-scale impacts and
volcanism have modified the structure and surface composition of the
lunar crust.

Platform Mounting Descriptions
==============================

The Gamma Ray Spectrometer is mounted on one of the three Lunar
Prospector booms.

Operational Considerations
==========================

The sensor housing is wrapped with a thermostat controlled heater
within a thermal blanket that will provide a stable operational
environment of -28 deg C for at least 1.5 years.  The ACS functions to
tag penetrating charged-particle events from the gamma ray spectrum
and to tag gamma rays that escape from the BGO.  The ACS also detects
neutrons using the boron content of the shield.
 
Operation and Sampling Modes
============================

The Gamma Ray Spectrometer is designed to operate continuously during
the Lunar Prospector Primary Mission.  It acquires a spectrum every 32
seconds.  The gamma ray energy range of the instrument covers 0.3 to 9
MeV with a sampling resolution of 17.6 keV.  The Lunar Prospector GRS,
as a function of energy, is 2 to 8 times more sensitive than the
Apollo gamma ray spectrometer.
 
Principal Investigator
======================

The Co-I and spectrometer group leader for the Lunar Prospector Gamma
Ray Spectrometer experiment is Dr. William Feldman of Los Alamos
National Laboratory. "

 END_OBJECT                    = INSTRUMENT_INFORMATION
  
 OBJECT                        = INSTRUMENT_REFERENCE_INFO
   REFERENCE_KEY_ID            = "BINDERETAL1998"
 END_OBJECT                    = INSTRUMENT_REFERENCE_INFO
  
END_OBJECT                    = INSTRUMENT
END