Among basic radioactive phenomena are: a-decay, ß-transformations (decays) и y-radiation. Processes related to beta-transformations are: ß- -transformation, ß+ -transformation, electronic capture. Except these processes the following phenomena are referred to the radioactivity phenomena: spontaneous fission, cluster activity, neutron activity, proton activity, beta-delayed transformations.
The concept of activity is used as the measure of radioactivity. The activity is the average number of radioactive transformations of definite nuclei per unit time. The measurement unit of the activity is becquerel (Bq); the activity of 1 Bq is correspondent to one transformation of a radionuclide in one second.
If the sources are situated out of an organism they expose it outside and, in this case one uses the term ‘external radiation’. If some radioactive sources appear in the human body (via air, water, drinks, food), then they say about ‘internal radiation’. In relation to exposure from man-made sources the two distinct groups of people are considered: members of the public, occupationally exposed individuals (personnel).