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The half-life period refers to the time it takes a radioactive material to disintegrate to half its original amount of radioactivity.

The Half-life Period is given by the formula
t_{1/2} = \frac{0.693}{\lambda}

where \lambda = disintegration constant

The half-life is not dependent on the amount of radioactive element, that is, the size of the material does not matter. Only the amount of radioactivity at any given time that matters.

Note: Longer the half-life period of a radioactive element, the more stable it is.

One of the most common uses of the half-life measurement is in the method of dating fossils. Depending on the amount of radioactivity available now, it is possible to estimate how old a fossil is.