# Co-60 is a beta emitter with a half-life of 5.3 years. Approximately what fraction of Co–60 atoms will remain in a particular sample after 26.5 years?

##### 1 Answer

Jan 20, 2017

The equation for radioactive decay is given by

where

In this case, it is actually the ratio

So, the portion remaining is 0.03125 or 3.125 % which is

Note that I used the exponential form of the equation. You could also use the (simpler) form

if you rather.