Airborne radiometric surveying is the process of detecting and mapping naturally radioactive minerals from rocks and soil. These minerals emit gamma rays which are naturally occurring from the gradual decay of three different elements:
The purpose of radiometric surveys is to determine the amount of these three different elements that exist in the surface of rocks and soil.
This naturally occurring radiation is detected with spectrometers. These spectrometers consist of two parts:
A detector which locates and records gamma rays, typically using a thallium activated sodium iodide crystal. As a gamma ray enters the sensor it creates an energy burst of light. This light is then converted into an electrical signal.
The analyzer, the second component, then takes this electrical signal and analyzes it and provides a visual readout.
There are many variables that must be considered and accounted for when acquiring radiometric data. Influences such as meteorological conditions, topography of the area, effects from the planets cosmic environment, height of the sensors and speed of the aircraft are just a few of the variables that need to be carefully accounted for.
Once these corrections are made, a ternary map can be produced which assigns colours to a topographical map based on results of the radiometric survey. It's important to note that terrestrial gamma rays originate from the surface and not from depth. Even a few inches of covering, such as soil, can absorb up to 100% of all rays. With this in mind, it is still possible that even smaller radiation results remaining in the exposed land can suggest a larger quantity located below the covering.
Airborne radiometric surveying's ability to locate Uranium, Thorium and Potassium anomalies make it a very useful and valuable prospecting tool for uranium. In comparison to airborne magnetometer surveying, which is capable of detecting and mapping magnetic material, the cost-to-benefit ratio of radiometric surveying is nearly the same.