<P> Radioactive contamination may also be an inevitable result of certain processes, such as the release of radioactive xenon in nuclear fuel reprocessing . In cases that radioactive material cannot be contained, it may be diluted to safe concentrations . For a discussion of environmental contamination by alpha emitters please see actinides in the environment . </P> <P> Nuclear fallout is the distribution of radioactive contamination by the 520 atmospheric nuclear explosions that took place from the 1950s to the 1980s . </P> <P> In nuclear accidents, a measure of the type and amount of radioactivity released, such as from a reactor containment failure, is known as the source term . The United States Nuclear Regulatory Commission defines this as "Types and amounts of radioactive or hazardous material released to the environment following an accident ." </P> <P> Contamination does not include residual radioactive material remaining at a site after the completion of decommissioning . Therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same . </P>

What are the main causes of radioactive pollution