Radioactive half-life (period)

The "half life" or “period” is one of the main characteristics of a radioactive nucleus. It is defined as the time required for the activity of a sample of this radionuclide to be divided by two. The period gives an idea of the life of the nucleus. The period does not depend on the age of the sample. The activity decreases rapidly with the number of half-lives: it is divided by 1000 after ten periods. For the management of radioactive waste, radioactive nuclei with half-lives below 30 years are said "short lived", while those whose half-lives exceeds 100 years are dubbed "long lived”. The radioisotopes used for medical diagnosis are in comparison very short-lived.

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