Formula for radioactive decay

A = A

_{0}* (1/2)^{(t/h)}where

- A = final amount
- A
_{0}= initial amount - t = time
- h = half life of element

With a little algebra, this formula can be transformed to give an equation to find the time (t), given the starting and ending amount.

ln( A/A_{0}) t = h ------------ ln( 1/2 )

To determine time required for a radioactive element with a half-life of 12.3 years (Tritium) to lose 25% of its mass (i.e., 75% remains)

ln(1/0.75)/ln(1/0.5)*12.3 = 5.1