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Instrument: GME : Goddard Medium Energy Experiment (IMP-8)
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Description
The Goddard Medium Energy (GME) Experiment on IMP-8 provided a comprehensive
basis for modulation and acceleration studies at 1 AU and a critical and unique
baseline at 1 AU for ongoing studies of cosmic ray modulation and propagation
in the outer heliosphere for Pioneer and Voyager investigations. These include
work at New Mexico State University, the University of New Hampshire, the
University of Maryland, the University of Iowa, Nagoya University, the
University of Tasmania and NASA/Goddard Space Flight Center.

The GME instrument has provided continuous observations extending over almost a
complete heliospheric cycle from launch in October 1973 to 2001. When combined
with the data from essentially identical Goddard experiments on IMP 6 and 7,
these cosmic ray and energetic interplanetary particle observations span a
period of 26 years. Data from the GME instrument span an energy range of
0.5-450 MeV Hydrogen, 2-450 MeV/nuc Helium, ions from Carbon through the Iron
group from several to >100 MeV/nuc and relativistic electrons. The quality of
the IMP 8 GME data in terms of particle and energy resolution, and sensitivity,
for galactic cosmic ray Hydrogen (2-230 MeV) and Helium (2-450 MeV/nuc) remains
comparable to that of any other cosmic ray experiment flown since 1971.

The GSFC cosmic-ray experiment was designed to measure energy spectra,
composition, and angular distributions of solar and galactic electrons,
protons, and heavier nuclei up to Z=30. Three distinct detector systems were
used. The first system consisted of a pair of solid-state telescopes that
measured integral fluxes of electrons above 150, 350, and 700 keV and of
protons above .05, .15, .50, .70, 1.0, 1.2, 2.0, 2.5, 5.0, 15, and 25 MeV.
Except for the .05-MeV proton mode, all counting modes had unique species
identification. The second detector system was a solid-state dE/dx vs E
telescope that looked perpendicular to the spin axis. This telescope measured
Z=1 to 16 nuclei with energies between 4 and 20 MeV/nucleon. Counts of
particles in the 0.5- to 4-MeV/nucleon range, with no charge resolution, were
obtained as counts in the dE/dx sensor but not in the E sensor. The third
detector system was a three-element telescope whose axis made an angle of 39
deg with respect to the spin axis. The middle element was a CsI scintillator,
while the other two elements were solid-state sensors. The instrument responded
to electrons between 2 and 12 MeV and to Z=1 to 30 nuclei in the energy range
20 to 500 MeV/nucleon. For particles below 80 MeV, this instrument acted as a
dE/dx vs E detector. Above 80 MeV, it acted as a bidirectional triple dE/dx vs
E detector. Flux directionality information was obtained by dividing certain
portions of the data from each detector into eight angular sectors. For further
details, see B. J. Teegarden et al., Astrophys. J., v. 202, p. 815, 1975.

For more information, see:
http://spdf.gsfc.nasa.gov/imp8_GME/GME_home.html