) 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.
There are a number of ways that this can happen and when it does, the atom is forever changed.
a technique for determining the age of minerals based on the occurrence in natural potassium of a small fixed amount of radioisotope 40K that decays to the stable argon isotope 40Ar with a half-life of 1.28x109 years.
Measurement of the ratio of these isotopes thus gives the age of the minerala technique for determining the age of organic materials, such as wood, based on their content of the radioisotope 14C acquired from the atmosphere when they formed part of a living plant.
Radioactivity and radioactive decay are spontaneous processes.
Students often struggle with this concept; therefore, it should be stressed that it is impossible to know exactly when each of the radioactive elements in a rock will decay.