The amount of time needed for a quantity (of substance) to decrease to half of its initial value is known as the half-life (symbol t12). In nuclear physics, the phrase is frequently used to indicate how rapidly unstable atoms decay radioactively or how long stable atoms last. The phrase is also used more broadly to describe any kind of exponential decay (or, very infrequently, nonexponential decay). The biological half-life of medications and other compounds in the human body, for instance, is a term used in the medical sciences. Half-opposite of life’s exponential growth is time’s doubling.
After Ernest Rutherford discovered the principle in 1907, the original word, half-life period, was abbreviated to half-life in the early 1950s. Rutherford measured the time it took for radium to decay into lead-206 in order to apply the idea of a radioactive element’s half-life to studies on dating rocks.
Half-life is a characteristic unit for the exponential decay equation and is constant across the lifespan of an exponentially decaying quantity. The reduction of a quantity is displayed in the accompanying table as a function of the number of half-lives that have passed.
Cobalt-60, a radioactive isotope used in radiotherapy, has a half-life of 5.26 years, for instance. As a result, after that time, a sample that contained 8 g of cobalt-60 at first would only have 4 g of cobalt-60 and would produce half as much radiation. Only 2 g of cobalt-60 would remain in the sample after an additional delay of 5.26 years. However, due to the unstable cobalt-60 nuclei decaying into stable nickel-60 nuclei, which remain with the still-undecaying cobalt, neither the volume nor the mass of the original sample visibly diminishes.
The distinctive characteristics of the many unstable atomic nuclei and the manner in which they decay are known as half-lives. Gamma decay is typically a faster process than alpha and beta decay. Beta decay half-lives can be as high as one-hundredth of a second, while alpha decay half-lives can be as high as one-millionth of a second. Although gamma emission half-lives have been observed to range widely, gamma decay half-lives (about 10–14 seconds) may be too short to quantify.
