Gamma-ray spectrometer

Complementing the x-ray spectrometer in an effort to characterise the surface composition was the gamma-ray spectrometer. This instrument was designed to detect two expected sources of gamma rays. One was from the nuclei of some
elements in the lunar surface, particularly iron, which will react to cosmic rays by cmiliing gamma rays of a precise energy. Another source came from the radioactive decay of other elements, especially the radioactive constituents of KREEPy material; potassium, thorium and uranium, whose gamma-ray emissions are of a w7ell-know7n energy. Mounted on the end of a 7.6-meirc boom that removed it from contaminating sources around the spacecraft, the gamma-ray spectrometer helped to paint a picture of the composition of the Moon along the spacecraft’s ground track.