The decay rates of isotopes are constant and are expressed as half-lives. Half-life is the known time for a radioactive material to decrease its radioactivity by one half of its initial value. Different materials have corresponding half-life constants which are then used as the basis for computing their age. Half-life can be calculated using the formula:
t(1/2) = ln(2)/k
where:
t(1/2) = half life
k = rate constant
