COSMOGENIC NUCLIDE DECAY PEAKS MADE IN GERMANIUM GAMMA-RAY DETECTORS.
Robert C. Reedy1. 1Institute of Meteoritics, MSC03-2050, Univ. New Mexico, Albuquerque, NM 87131 USA.
<rreedy@unm.edu>
Introduction: Cosmic-ray particles produce many
backgrounds in gamma-ray detectors in space, some of
which interfere with gamma rays of interest from the
studied object. Most background peaks in gamma-ray
spectra come from the matter around the detector, but
some peaks come from reactions in the detector itself
[e.g., 1-3]. Presented here are background peaks from
radionuclides made in the high-resolution germanium
detectors used for many space missions.
Most early gamma ray spectrometer (GRS) systems
used low-resolution scintillators (e.g., NaI), and few
peaks were observed in their spectra. Many more
peaks are resolved in Ge detectors. Weaker peaks can
be identified in Ge detectors, but backgrounds are of-
ten more important for many of such weaker peaks.
Most Ge detectors in space until recently were used for
astrophysics (e.g., HEAO-3 [3]), but now Ge detectors
are being used for planetary missions (Mars Odyssey,
MESSENGER, and Kaguya-SELENE).
Backgrounds are important for most elements
measured by Ge-GRS systems for planetary [1,4] or
astrophysical [2,3,5] space missions. Such back-
grounds are also seen in Ge-GRS systems flown to
near the top of the atmosphere by balloons, in labora-
tory experiments with energetic particles, and even in
low-level counting systems on the Earth’s surface.
No peaks are observed from prompt reactions in-
duced by protons because the proton deposits energy
in the detector. Fast-neutron inelastic reactions with
Ge nuclei make broad, asymmetric peaks when energy
from the nucleus’ recoil sums with that from a gamma
ray [e.g., 1,2]. If the spacecraft is large enough or
there are planetary leakage thermal neutrons, narrow
peaks are made by Ge(n,γ) reactions [e.g., 1,2].
Many radionuclides are made in Ge detectors.
However, no peaks are pro