Activity is defined as the rate of decay (or number of disintegrations per second) of a substance.

Half life is the time taken for half of the radioactive nuclei present to decay or the time taken for the activity of a sample to halve.

Carbon-14 Dating is a useful example of the concept of half-life in practice. Carbon-14 is a radioactive isotope of carbon with a half-life of 5730 years.

Decay constant is the fraction of the total number of nuclei present that will decay in a unit time.

Radioactivity

A = λN

λ = 0.693/ t _½

N = N_oexp(-λt)

A = A_oexp(-λt)

Radioactivity

A = activity of a sample. (Units: Becquerel, Bq.) Activity depends on number of particles present initially.

A_o = activity at the start

N = number of atoms

N_o = the number of atoms at the start

λ = the decay constant

t _½ = half life

t = time