Subsurface Detection - Nuclear Survey Methods

Nuclear survey methods are of two basic types. The more common of the two involves measurement of natural radioactivity in rocks or soils. This method might be used, for example, to identify potential uranium ores for mining. In this case a hand-held geiger counter could be employed. Another use is to measure the natural gamma ray emissions from rock formations in a drill hole when searching for oil. A gamma ray counter is lowered down the hole on a wire, and the natural gamma ray emissions of the rocks in the borehole wall are measured. Different rocks exhibit various levels of radioactivity, making remote identification of rock type possible. Geophysical surveys of boreholes that are done in this manner are called wireline surveys or wireline bogs.

The second type of nuclear survey method is stimulated radioactivity. In this method, a radioactive source is used to bombard a rock and induce radioactive decay in the rock. The level of induced radioactive decay is measured and the rock type is interpreted from the measurements. Wireline surveys employing this method are often used when exploring for oil.