Radionuclides
This information is provided by Baltimore County:
Radionuclides occur naturally as trace elements in rocks, soils, and ground water as a consequence of the radioactive decay of uranium, and thorium. This decay occurs because these elements are unstable; they continually release energy into the environment until a stable, non-radioactive substance is formed. This energy is part of the natural radiation to which all living creatures are exposed. Radon, radium, and uranium are the most common radioactive elements found in ground water. Other naturally occurring radionuclides tend to be environmentally immobile, or have short half-lives, meaning they are far less likely to be found in significant amounts in ground water.
Radioactivity is a measure of the energy that is released during the decay process. The energy or radiation can be in the form of a wave (for example, gamma rays) or a particle (for example, alpha and beta particles) or both. Scientists can identify the different types of radioactive elements by measuring the characteristics of this energy. In the U.S., radioactivity is measured in units called “curies.” The level of radioactivity in water is very low and is measured in picocuries per liter, written pCi/l (one picocurie equals one-trillionth of a –12 curie or 10 ).
To assess the level of radionuclides in drinking water, the water supply is typically first tested prior to any treatment for short-term gross alpha (also referred to as gross alpha particle activity (GAPA)) and gross beta (gross beta particle activity (GBPA)). These tests are used as cost-effective screening tools used to determine whether further isotope-specific testing for radium and uranium is warranted.