## Quick Reference

Suppose that *y*=*Ae*^{kt}, where *A* (>0) and *k* are constants, and *t* represents some measurement of time (see exponential growth). When *k* <0, *y* can be said to be exhibiting exponential decay. In such circumstances, the length of time it takes for *y* to be reduced to half its value is the same, whatever the value. This length of time, called the half-life, is a useful measure of the rate of decay. It is applicable, for example, to the decay of radioactive isotopes.

http://www.edumedia-sciences.com/a100_l2-radioactive-decay.html An animation showing the physical decay and corresponding graph of three radioactive isotopes. (Subscription)

*Subjects:*
Mathematics.