Introduction

Since the discovery of radioactivity (H. Becquerel, 1896), studies of the radioactivity of rocks and minerals have found applications in many fields of geology and geophysics. First, the rate of radioactive decay of certain naturally occurring elements in rocks provides a powerful means of dating geological events, in particular the times of formation of rocks. Second, the heat produced by radioactive disintegrations in various types of crustal rocks is of importance in studies of thermal conditions in the subsurface. Third, radioactivity surveys are of use in geological mapping as different rock types can be recognized from their distinctive radioactive signatures. Probably, the most common application of radiometric techniques is in geophysical borehole logging for estimation of rock porosity and detection of fractures and underground movement of fluids (Section 11.3.3).

Radioactivity is part of our physical environment. The largest contribution to the radiation field is of natural origin; it is due to cosmic rays, the natural radioactivity of the grounds, and the radioactive decay products of radon in the air. Artificial radioactivity is emitted by nuclear power plants, industrial plants, and some research laboratories. These emissions are very small in normal operation, although large amounts of radioactivity can be released to the environment through accidents. One of the most publicized was the nuclear accident at Chernobyl, Ukraine (April 26, 1986), which caused a serious concern because of the risk to public health in the areas affected by high levels of radiation exposure.