Half life

It is convenient to introduce the **half-life**, *T*_{1/2}, of a
substance, defined as the time after which exactly one half of a the
originally active nuclei
remain. In terms of this, the number of nuclei *N* remaining at
time *t*, given *N*_{0} at time *t* = 0, is given by

Thus, after a period of one half-life,
of a substance
remains, after another half life
`x`
=
of a substance remains, and
so on. Half-lives of substances range
from tiny fractions of a second to millions of years.

1999-09-29