Activity as a function of time

Finding the amount remaining, (proportional the activity of the sample in Bq), after a whole number of half lives is a simple matter. Count half-lives on your fingers.

To find the activity after any given time, use the activity equation.and your calculator....

If you are given the half life, not the decay constant, use the equation....

.... to convert one to the other.

Two micrograms of ¹⁴C have a half-life of 5730 years. The amount remaining after 20,000 years (N) is given at once, by ...