Radiometric
Radiometric investigations in geophysics are applied to measure radiation emitted by natural or artificial isotopes, neutrons resulted in some nuclear reactions or to evaluate natural radioactive fond.
Alpha radiation consist of helium He42 nuclei. The initial energy of the particle is a characteristic of every emitting element and a key parameter useful to identify it (alpha spectroscopy) . The distance line of a particle depends on energy but is no more than centimeters, in air and millimeters, in rocks .
Beta radiations are made of electrons only, having speeds between zero and light speed, penetrating no more than 10 m in air and 1 cm, in rocks. There are some categories : b- , emitted by natural or artificial radioactive elements, b+ , emitted by artificial radioactive elements and mono-energetic electrons resulted from internal conversion.
Gamma radiation has an electromagnetic origin (see EM spectra where some domains must be added : IR (infrared) and UV (ultraviolet), 10E12-10E16 Hz, X radiations, 10E16-10E20 Hz, gamma radiations, 10E18-10E21 Hz and cosmic radiations, >10E21Hz) and it is emitted by nucleus, during energetic equalization after a particle emission or catching. Gamma radiation interact with electronic cover (Thompson dispersion, Compton effect), with nuclei's electric field ( pair producing) or with nucleus (photo-nuclear reactions). Attenuation law of gamma radiation is similar with the beta radiation’s one, except the unlimited route. In this case the ‘half distance’ parameters is used.
Neutrons result from natural or artificial nuclear reactions and they are not emitted by natural radioactive elements. Their interaction with materials consist of slowing reactions, diffusion or catching. There are many methods used in geophysics or industry to investigate geological features or materials quality, using artificial neutron sources.
The primary cosmic radiation is a nuclei flux accelerated to 10E9-10E18 eV. As a result of collisions with different atoms met in atmosphere is the secondary cosmic radiation.
The isotopes of heavy elements are a and b radioactive and atomic number (A) can be modified with no more than 4 units; in nature, only 3 from 4 possible radioactive families are present, each of them containing one radioactive gas, radon’s isotope, a active, and having distinctive half time periods. They permit the identification of those isotopes by measurements.
Instruments used in radiometry can measure the total effect or the individual one, for elements such as Uranium, Thorium, Potassium, in spectral domain, to identify specific radioactive sources.
In geology domain, measurements on radioactivity are used to explore radioactive minerals, to detect, in some cases, faults, voids, groundwater, zones of alterations, hydrocarbons, contaminants. Also site assessments, before implementing residential projects, can reveal an anomalous and increased background of radioactivity.
