Half-life
Half-life
|
Number of half-lives elapsed |
Fraction remaining |
Percentage remaining |
|
|---|---|---|---|
| 0 | 1/1 | 100 | |
| 1 | 1/2 | 50 | |
| 2 | 1/4 | 25 | |
| 3 | 1/8 | 12 | .5 |
| 4 | 1/16 | 6 | .25 |
| 5 | 1/32 | 3 | .125 |
| 6 | 1/64 | 1 | .563 |
| 7 | 1/128 | 0 | .781 |
| ... | ... | ... | |
| n | 2-n | 100/(2n) | |
Half-life is closely related to the property of Radioactive Decay and represents the time taken for half the Atoms in a Radioactive substances to undergo decay and change into another nuclear form (either a radioactive daughter product or a stable
alf-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms (radioactive decay), but it may apply to any quantity which follows a set-rate decay.
The original term, dating to 1907, was "half-life period", which was later shortened to "half-life" in the early 1950s.]
Half-lives are used to describe quantities undergoing exponential decay—for example, radioactive decay—where the half-life is constant over the whole life of the decay, and is a characteristic unit (a natural unit of scale) for the exponential decay equation. However, a half-life can also be defined for non-exponential decay processes, although in these cases the half-life varies throughout the decay process. For a general introduction and description of exponential decay, see the article exponential decay. For a general introduction and description of non-exponential decay, see the article rate law. Corresponding to sediments in environmental processes, if the half-life is greater than the residence time, then the radioactive nuclide will have enough time to significantly alter the concentration. The converse of half-life is doubling time.
The table on the right shows the reduction of a quantity in terms of the number of half-lives elapsed.
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