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Radioactive Decay

Radioactive materials have an associated half-life, or decay time characteristic of that isotope. As radiation is emitted, the material becomes less radioactive over time, decaying exponentially. Since it is impossible or impractical to measure how long one atom takes to decay, the amount of time it takes for half of the total amount of radioactive material to decay is used to calculate half-life. Some radioisotopes have long half-lives; for example, ¹⁴C takes 5,730 years for any given quantity to decay to half of the original amount of radioactivity. Other radioactive materials have short half-lives; ³²P has a two week half-life, and ⁹⁹Tc^m (used in human and animal nuclear medicine diagnostic procedures) has a half-life of 6 hours.

This is important for many reasons. When deposited in the human body, the half life of the radioactive material present in the body affects the amount of the exposure. If the radioactive material contaminates a workbench or equipment, and is not removable, the amount of time before the contaminated items may be used again is determined by the radioactive half-life. Radioisotope decay using half-life minimizes costs and concerns in radioactive waste management.

The equation which is used to calculate radioactive decay is shown below.