What happens to the decayed portion of a radioactive element after the element reached it's half life?

Answer 1

When a radioactive material undergoes radioactive decay, except spontaneous fission, a daughter product is formed. The daughter may or may not be radioactive. If it is, this daughter product begins its own evolution according to its decay scheme and its own half-life. Any daughter products from that decay event will either be stable or will decay according to how (un)stable the daughter is and what its half-life happens to be. The original radionuclide continues to decay in its own way. You can see a "dynamic" developing here. The fact that a radioactive material has a half-life doesn't speak to what happens to the material or to its daughter products. It is only a measure of the rate of decay of a material. Radioactive materials decay according to what they are, and their daughter products will, if they are not stable, undergo decay as well, each according to its own decay scheme. The half-life only puts a timeline on things. And it (the half-life idea) must be applied to each unstable daughter. A consequence of radioactive decay and inspection of the daughter products allows us to use radioactive decay schemes to date materials. There are a number of radionuclides that are useful in doing this, and the decay schemes are well known. We understand the decay rates of the original material and also its daughters, and by counting all of them, we can "rewind time" to the period when they were isolated and state with good accuracy when the material was sequestered. Different methods of dating materials might be applied, depending on the material and its age.

Answer 2

After a radioactive element reaches its half-life, half of the original amount will have decayed into a stable daughter product. The decayed portion continues to undergo further radioactive decay until it reaches a stable state, usually through a series of decay processes involving different daughter products.