The decay rate is 3.9% per year.
There are three main types of radiation, called alpha, beta and gamma radiation, which all have different properties. The half-life of a radioactive isotope is the time taken for half its radioactive atoms to decay. Nuclear equations describe what happens during alpha and beta decay.
The nuclei of radioactive atoms are unstable. They break down and change into a completely different type of atom. This is called radioactive decay.
The radioactivity of an object is measured by the number of nuclear decays it emits each second – the more it emits, the more radioactive it is.
It is not possible to predict when an individual atom might decay. But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay. This is called the half-life of the radioactive isotope.
There are two definitions of half-life, but they mean essentially the same thing. Half-life is the time taken for:
The number of nuclei of the radioactive isotope in a sample to halve
The count rate from a sample containing the radioactive isotope to fall to half its starting level
Different radioactive isotopes have different half-lives. For example, the half-life of carbon-14 is 5,715 years, but the half-life of francium-223 is just 20 minutes.
You can use this online Half Life Calculator shared by Calculator.net.