They undergo radioactive decay. Radioactivity is found in naturally occurring sources and in artificially produced ones. People are constantly being exposed to radiation from a variety of natural and human-created sources. Exposure should be minimized, but it can never be reduced to zero. Special detectors are needed.
Radiation has an effect on tissue and on genetic material.
Several devices have been developed to detect radioactivity, with the earliest being an unexposed photographic plate placed in the vicinity of a source being detected. Dosimetry is the measurement of radiation and the study of its effects on living organisms. There are several different units used to measure radiation. The quality factor is a number assigned to each type of radiation to describe its biological effects. The effect that absorbed radiation has on different types of tissues varies.