The count rate drops from 80 to 40 counts a minute in two days, so the half-life is two days. The decay curve for a radioactive substance The graph shows the decay curve for a radioactive substance. It is possible to find out the half-life of a radioactive substance from a graph of the count rate against time. For example, the half-life of carbon-14 is 5,715 years, but the half-life of francium-223 is just 20 minutes.

the time it takes for the count rate from a sample containing the isotope to fall to half its starting levelĭifferent radioactive isotopes have different half-lives.

the time it takes for the number of nuclei of the isotope in a sample to halve.

There are two definitions of half-life - but they mean essentially the same thing: This is called the half-life of the radioactive isotope. But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay. It is not possible to predict when an individual atom might decay. As this breakdown occurs, the activity of any radioactive source becomes less. įor example, carbon-14 decays to nitrogen-14 when it emits beta radiation. They breakdown and change into a completely different type of atom. The nuclei of radioactive atoms are unstable.

Half life 3 beta