Another way of expressing this is the half-life period (given the symbol T).
The half-life is the time it takes for half of the parent atoms to decay.
The unstable or more commonly known radioactive isotopes break down by radioactive decay into other isotopes.All living organisms take up carbon from their environment including a small proportion of the radioactive isotope 14C (formed from nitrogen-14 as a result of cosmic ray bombardment).The amount of carbon isotopes within living organisms reaches an equilibrium value, on death no more is taken up, and the 14C present starts to decay at a known rate.Radiocarbon or Carbon-14 dating is a technique used by scientist to date bones, wood, paper and cloth. It is produced in the Earth’s upper atmosphere when Nitrogen-14 is broken down to form the unstable Carbon-14 by the action of cosmic rays.The unstable Carbon-14 is transported down to the lower atmosphere by atmospheric activity such as storms.This decay process leads to a more balanced nucleus and when the number of protons and neutrons balance, the atom becomes stable.This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.The unstable Carbon-14 within the organism begins to decay to form Nitrogen-14 by emitting a beta particle.Over time there is a gradual decrease in the amount of Carbon-14 and the ratio of Carbon-14 atoms to other Carbon atoms declines. Therefore half of the Carbon-14 has decayed after 5730 years.Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.These are released as radioactive particles (there are many types).