Radioactive background is a natural part of the surrounding area of the earth´s surface, its source is the cosmic rays and radioactivity of the rocks. Radionuclide methods include two basic kinds of research allowing to structurally differentiate the field of survey and characterise the features or components present in the evaluated area.

The basic method of quantitative assessment is the registration of the natural radioactivity of rocks upon which it is possible to determine the type of rock, the source area of the original material, conditions during the formation of rocks or shear zones whose presence indicate a contrast increase in the amount of registered radiation. Spectral radiometry provides a conclusive identification by determining of the energy levels of the received gamma quanta which provides the data necessary to estimate the proportional representation of building elements.

The previous section mentioned methods are used for standard surface survey as well as in the emanometry survey; Emanometry - analysis of soil air taken from a depth of min. 0.8 m.

The active radionuclide survey methods used artificial sources being either a chemical source of neutron particles and gamma-rays, or electronic source of neutron particles. Active methods are invaluable when determining petrophysical properties of rocks and identification of additional environmental components and their proportional representation.