# Half life dating equation

Nevertheless, when there are many identical atoms decaying (right boxes), the law of large numbers suggests that it is a very good approximation to say that half of the atoms remain after one half-life.There are various simple exercises that demonstrate probabilistic decay, for example involving flipping coins or running a statistical computer program.The biological half-life of caesium in human beings is between one and four months.Half-life, in radioactivity, the interval of time required for one-half of the atomic nuclei of a radioactive sample to decay (change spontaneously into other nuclear species by emitting particles and energy), or, equivalently, the time interval required for the number of disintegrations per second of a radioactive material to decrease by one-half.For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the human body. The original term, half-life period, dating to Ernest Rutherford's discovery of the principle in 1907, was shortened to half-life in the early 1950s.

A half-life usually describes the decay of discrete entities, such as radioactive atoms.

For example, the image on the right is a simulation of many identical atoms undergoing radioactive decay.

Note that after one half-life there are not exactly one-half of the atoms remaining, only approximately, because of the random variation in the process.

Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation.

The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed.

The radioactive isotope cobalt-60, which is used for radiotherapy, has, for example, a half-life of 5.26 years.