Radioactivity surveying measures the natural radioactivity due to potassium, thorium, and uranium in near-surface rocks, which has applications in geological and geochemical mapping, and is used to find ores of uranium and thorium or other types of ore that have associated radioactivity. It also has environmental applications, mapping radon, a hazard to health, in surface rocks and waters.
The most common surveying method detects γ rays, which can be used to identify the source element as well as detect the presence of radioactivity, and can be employed in ground or airborne surveys, but radon measurement often requires sampling below the surface.
Radioactive radiations
The previous chapter explained how radioactivity could be used to date rocks because isotopes decay from one element to another. This chapter is mainly concerned with the ‘radiations’ that accompany the decays, as a way of detecting and identifying the source elements. There are three principal types of radiation, all of which originate from the nuclei of radioactive atoms (Section 15.12.1). α-particles consist of two protons and two neutrons, and so have a positive electrical charge (ultimately, they each combine with two electrons to form helium atoms, and this is the origin of the helium used to inflate balloons). β-particles are electrons – produced when a proton converts to a neutron plus a electron – and so have a negative charge. Because of their electric charges, α-and β-particles cannot travel far through matter, no more than a few centimetres in air, or a few millimetres of rock, and so are little used in surveying.
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