Law of Radioactive Decay
The principle that the rate of decay is proportional to the number of undecayed nuclei present.
Formula / equation
N = N₀ e^(−λt)
Unit
Dimensionless
In depth
Radioactive decay is a first-order process, giving an exponential fall in both the number of nuclei and the activity. The law is statistical: it predicts the behaviour of large populations precisely while saying nothing about when any individual nucleus will decay.
Examples in the real world
A sample retaining one eighth of its original activity after three half-lives.