Many nuclides can decay in more than one way (e.g. by both alpha and
beta decays). In this case each decay process is characterised by its
own decay constant. We consider decay by two processes with decay
constants 
and 
. This is easily generalised.
Then
where 
is that number decaying by path 1, etc.
Let 
. Then the overall decay
is determined by this sum of decay constants,
It follows that
The ratio 
gives the fraction of nuclei
decaying by path 1 and is known as the branching ratio.