Radiometric Methods

The presence of radioactive elements can be determined by the familiar geiger counter. This instrument measures the energy which is released during the process of radioactive decay. For example, three types of rays are given off as a uranium molecule decays, these rays are: gamma, alpha and beta. Of these rays, the gamma ray is the most penetrating and due to this it is the most likely to be detected by the geiger counter. Because the geiger has a low sensitivity and a low operating efficiency, it has been supplanted in many applications by an instrument known as the scintillometer or scintillation counter.

Gamma-ray spectrometers are an even more advanced version of the scintillation counters. The gamma-ray spectrometers can distinguish between radiation from the three principal radioactive elements that occur in nature – thorium, potassium anduranium – by measuring the energy of the radiation. Radiometric surveying can be done from aircrafts too.

To detect showings of radioactive minerals directly, ground radiometric surveys are the most useful. Airborne radiometric surveys are most of the time used for geological mapping, due to the fact that the radioactive elements happen in greater abundance in granitic rocks. Down-hole probes are very often used to measure the radioactivity of rock units which are encountered in drill holes.