Specific activity several other biomedical applications. Specific activity Specific activity is the activity per quantity of a radionuclide and is a physical property of that radionuclide. Activity is a quantity related to radioactivity. The SI unit of activity is the becquerel (Bq), equal to one reciprocal second. The becquerel is defined as the number of radioactive transformations per second that occur in a particular radioactive isotope. Its related non-SI unit equivalent is the Curie (Ci) which is transformations per second. Since the probability of radioactive decay for a given radionuclide is a fixed physical quantity (with some slight exceptions, see changing decay
Environmental radioactivity Environmental radioactivity Environmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 (Sr) and technetium-99 (Tc), are only found on Earth as a result of human activity, and some, like potassium-40 (K), are only present due to natural processes, a few isotopes, "e.g." tritium (H), result from both natural processes and human activities. The concentration and location of some natural isotopes, particularly uranium-238 (U), can be affected by human activity. Radioactivity is present everywhere, and has been since the formation of the earth. According to the IAEA, soil typically contains the following four