This is called the half-life. Key fact Half-life is the time it takes for the activity of the source to fall to half its original value. The illustration below shows how a radioactive sample is ...

0.0625 of the original sample This could then be incorporated into other data. So, if the half-life is two days, four half-lives is 8 days. If a sample has a count rate of 3,200 Bq at the start ...