Charged-particle induced radiation damage of a HPGe gamma-ray detector during spaceflight

Details Charged-particle induced radiation damage of a HPGe gamma-ray detector during spaceflight Charged-particle induced radiation damage of a HPGe gamma-ray detector during spaceflight

Feb 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999nimpa.422..586e&link_type=abstract

Nuclear Instruments and Methods in Physics Research Section A, Volume 422, Issue 1-3, p. 586-590.

Physics

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Scientific paper

The Mars Observer spacecraft was launched on September 26, 1992 with a planned arrival at Mars after an 11-month cruise. Among the scientific instruments carried on the spacecraft was a Gamma-Ray Spectrometer (GRS) experiment to measure the composition of Mars. The GRS used a passively cooled high-purity germanium detector for measurements in the 0.2-10MeV region. The sensor was a closed-end co-axial detector, 5.5cm diameter by 5.5cm long, and had an efficiency along its axis of 28% at 1332keV relative to a standard NaI(Tl) detector. The sensor was surrounded by a thin (0.5cm) plastic charged-particle shield. This was the first planetary mission to use a cooled Ge detector. It was expected that the long duration in space of three years would cause an increase in the energy resolution of the detector due to radiation damage and could affect the expected science return of the GRS. Shortly before arrival, on August 21, 1993, contact was lost with the spacecraft following the pressurization of the propellent tank for the orbital-insertion rocket motor. During much of the cruise to Mars, the GRS was actively collecting background data. The instrument provided over 1200h of data collection during periods of both quiescent sun and solar flares. From the charged particle interactions in the shield, the total number of cosmic ray hits on the detector could be determined. The average cosmic ray flux at the MO GRS was about 2.5cm-2s-1. The estimated fluence of charged particles during cruise was about 108 particles cm-2 with 31% of these occurring during a single solar proton event of approximately 10 days duration. During cruise, the detector energy resolution determined from a background gamma-ray at 1312keV degraded from 2.4keV full-width at half-maximum shortly after launch to 6.4keV 11 months later. This result agrees well with measurements from ground-based accelerator irradiations (at 1.5GeV) on a similar size detector.

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