# Formula Radioactive Decay Half-life Decay constant

## Half-life

`$$ t_{\text h} $$`Unit

`$$ \mathrm{s} $$`

Half-life is the period of time after which the initial amount of atomic nuclei has decayed to half.

## Decay constant

`$$ \lambda $$`Unit

`$$ \frac{1}{\mathrm s} $$`

Decay constant specifies the probability of decay per unit of time. In other words: The decay constant determines how fast a nuclide (radioactive substance) decays. Different nuclide decay at different rates.

The reciprocal of the decay constant is the *lifetime*: \( \tau = \frac{1}{\lambda} \).