8. Radioactivity (for the record)

The radioactive properties of materials are used in civil engineering reconnaissance almost exclusively in the form of logs (natural radioactivity logs and induced radioactivity logs: γ – γ to measure the in-situ density of materials, neutron-neutron to measure their in-situ water content) (see [C 225] ).

In surface geophysics, only the radon content of gases trapped in topsoil is sometimes measured in order to detect underground cavities (whose presence causes radon to be released from the surrounding material). This method is not highly developed.