Radiometrics

Radiometric surveys measure the distribution of three radioactive elements (uranium, thorium and potassium) in the Earth's crust, by recording the gamma-ray radiation emitted during the decay of these elements. Approximately 90% of measured gamma rays are received from the top 30cm of the ground. These measurements enable the interpretation of rock and soil types.

Radioactivity refers to the process by which an unstable atom becomes stable through the breakdown, or decay, of its nucleus. In the process of decay, radioactive elements can emit any of three distinct types of rays, named by the first three letters of the Greek alphabet; alpha, beta and gamma. A gamma ray is pure energy and unlike alpha and beta rays it is electrically neutral. Gamma rays are similar to visible light, being parcels of electromagnetic radiation. Unlike visible light they have much higher energy and frequency. Of the three types of radioactive rays, gamma rays with such high energy and no charge, are the most difficult to stop.

Radioactive elements occur naturally in the crystals of some minerals. The abundance of these minerals containing the radioactive elements changes from rock type to rock type. Therefore, major changes in rock types are normally associated with changes in the gamma radiation released. Weathering (chemical and physical breakdown) and metamorphism (physical and chemical changes to rocks caused by changes to heat and pressure) also play a part in the distribution of these elements.

Any geological process that concentrates minerals may concentrate radioactive elements. These areas will emit an anomalous gamma-ray reading to the background rocks.

Radiometrics can be done through airborne or ground surveys.

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