what is the time necessary for 99.9%of the atoms of a radioactive compound to be disintegrated? t½=5times.
.001=e^-.692t
where t is in halfflives...
ln(.001)=.692t
-6.91=-.692t
t=10 halflives...
Lets look at five halfflives...
xxx=e^-.692*5
xxx= 0.031429762 or .97 is gone in five halflives...