Radioactive isotope dating definition
This is an example where the half-life reduces as time goes on.(In other non-exponential decays, it can increase instead.) The decay of a mixture of two or more materials which each decay exponentially, but with different half-lives, is not exponential.The number at the top is how many half-lives have elapsed.Note the consequence of the law of large numbers: with more atoms, the overall decay is more regular and more predictable.) is the time required for a quantity to reduce to half its initial value.The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay.As an example, the radioactive decay of carbon-14 is exponential with a half-life of 5,730 years.A quantity of carbon-14 will decay to half of its original amount (on average) after 5,730 years, regardless of how big or small the original quantity was.
Simulation of many identical atoms undergoing radioactive decay, starting with either 4 atoms per box (left) or 400 (right).
Because atmospheric carbon 14 arises at about the same rate that the atom decays, Earth's levels of carbon 14 have remained fairly constant.
Once an organism is dead, however, no new carbon is actively absorbed by its tissues, and its carbon 14 gradually decays.
For example, if there is just one radioactive atom, and its half-life is one second, there will not be "half of an atom" left after one second.
Instead, the half-life is defined in terms of probability: "Half-life is the time required for exactly half of the entities to decay on average".