Radioactive elements obtained artificially end up transforming themselves into other isotopes until they become a stable isotope like bismuth. All the transmutations occur by means of alpha and beta emission.
All the nuclei which procede from the initial one are called a radioactive series or  radioactive family.
The following visual shows the Plutonium series. The mass number of the isotopes of the series can be calculated from the formula A=4n+1. In which n is a natural number from 60 to 52. The stable isotope which ends the series is bismuth.
You can see the natural radioactive series by clicking here.