Diagram of the Apollo 15 & 16 Gamma-ray Detector

The Apollo 15 and 16 command modules carried a 512-channel cylindrical NaI(Tl) scintillation gamma-ray spectrometer, 76 x 76 mm in size, covered with a plastic scintillator for charged particle rejection. The instrument covered the energy range 0.55-8.6 MeV. The resolution of the spectrometer was about 8%. The sensor was mounted on a 7.6 m long boom.

Primarily intended to study the Moon's radioactivity, it made measurements of the cosmic gamma-ray background during its trip. A flux density of ~1 x 104 quanta/sq-m/s was observed.

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