Radioactive decay
Radioactive emission of alpha and beta particles and gamma rays take place due to radioactive decay. Radioactive decay is the process of unstable nuclei disintegrating to attain more stability. This process is not affected by:
chemical combinations or reactions;
any changes in physical conditions such as temperature, pressure, electric or magnetic fields etc.
Therefore, radioactive emission is a random process, the rate of decay is proportional to the number of unstable nuclei present. When a radioactive element decays, a constant fraction of the larger number of unstable nuclei will decay in a certain time. A measure of the rate of decay is the half-life of the radioactive element:
The half-life of a sample of radioactive element is defined as the time taken for half of the unstable nuclei to decay.
Each radioactive element has its’ own half- life. E.g. the half-life of radioactive sodium is 15 years, whereas that of radium is 1600 years. To measure the half-life of a radioactive substance, the rate of decay (activity) has to be measured at different times, which can easily be found finding the count rate using a G-M tube and a rate meter.