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 emitting 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 also of a well-known energy. Mounted on the end of a 7.6-metre boom that removed it from contaminating sources around the spacecraft, the gamma-ray spectrometer helped to build up a picture of the composition of the Moon along the spacecraft's ground track.
Was this article helpful?