The Shuttle activation monitor: a system for direct comparison of gamma-ray detector materials in a space environment

An experimental system which was used to compare gamma-ray detector materials in a space environment is described. Two 3-in×3-in scintillator detectors, NaI and BGO, were flown on the Space Shuttle Columbia as part of the Shuttle Activation Monitor (SAM) experiment. The goals of this experiment were to compare the performance of the two detector materials in the same environment and to measure the variations in dynamic radiation background as a function of geomagnetic coordinates, amount of shielding, and type of detector material. Twenty-four hours of data in 5-min time bins were recorded with each detector in both high-shielding and low-shielding locations in the Orbiter middeck. The high-inclination orbit (57°, 160 nmi) provided exposure to the trapped charged particles in the South Atlantic Anomaly as well as the electrons in the polar regions. The system used specially adapted off-the-shelf hardware for data acquisition and storage. The multichannel analyzer was a commercially available unit with added circuitry to support an active particle shield. Data during the flight were stored using a cassette tape recorder. A preliminary look at some of the data from the first flight is included