Figure 10.4
Decay scheme for^60 Co.step decay where the daughter nuclide is stable, the rate of decay (disintegrations s–^1 ) is simply
expressed, i.e. for
The number of undecayed nuclei present at time t, is given by the exponential form of the same
equation, i.e.
A plot of log 10 Nx against t is a straight line. A quantity of practical importance is the time taken for the
number of parent nuclei to reduce to half the original number. This time is known as the half-life, t1/2,
and is inversely related to the decay constant.
Its value is thus characteristic of a particular radionuclide and is a further aid to identification.
When the daughter Y undergoes further decay the mathematical treatment of the system rapidly
becomes complex. For example, in a two-step decay
the number of nuclei of Y at time t is given by
Analytical calculations based upon equations of this complexity are not very fruitful, particularly as
they depend upon detecting both radioactive