Radionuclide pollutants
Radionuclides, also called radioisotopes, are chemical species whose nuclei are unstable and dissipate excess energy by spontaneously emitting ionizing radiation. For pollution monitoring, alpha particles (helium nuclei), beta particles (electrons) and gamma photons are detected in the energy range tens of keV (kiloelectron volt) to MeV (megaelectron volt). Their activity is measured mainly using semiconductor and scintillation detectors, as well as ionization chambers.
Activity is the number of decaying nuclei per second in some amount of radionuclide material, measured with the unit Becquerel (Bq), representing one decay per second. For radionuclide monitoring, derived quantities and units are used: Bq/m3 for concentration in air, Bq/L for concentration in water and Bq/kg for concentration in soil. Currently, about a thousand of radionuclides are known, both natural and artificial, but only tens of them are typically measured.