Alpha Particle Spectrometer

Description

This experiment was designed to determine the lunar surface radon evolution and, in so doing, to combine with the other geochemical experiments (gamma-ray spectrometer, 71-063A-08, and X-ray flourescence, 71-063A-09) in determining lunar surface composition and identifying localized sources of enhanced radon emission that may correspond to regions of enhanced lunar outgassing. The data obtained on the gross rate of surface radon evolution and on localized sources of enhanced radon emission were to be used in constructing radiation maps showing lunar surface inhomogenities. Measurements of alpha particle emission from deep space background were made during lunar orbit and transearth coast. The spectrometer used in this experiment was composed of a 2 by 5 array of 10 silicon surface barrier detectors housed in the same enclosure as the X-ray flourescence experiment. Each of the 10 sensors looked toward the moon with a 90-deg full-angle field of view. Each sensor had its own preamplifier, the outputs of which fed into a common analog-to-digital converter that in turn sorted the pulses into 256 energy channels in the range 4.5 to 9.0 MeV. The instrumentation was designed to turn off the other nine detectors once an event was registered in one of the detectors until the event had been analyzed. Pulse height channel information for up to a bit rate limited value of 10 events per second was telemetered. The average alpha particle rate encountered was about 1 count/sec. Controls were available in the command module to activate or deactivate the experiment. The experiment performed normally throughout the mission.