Question

Thorium 32 has a half life of 1.4*10^110 years
At a particular instant the activity of a sample of thorium is 120 Bq
Calculate the time taken for the activity of this sample to fall to 15Bq

Answer 1

n(t) = n(0) (0.5)^t'

t' = time/half-life

15/120 = (0.5)^t'

log(15/120) = (t') log (0.5)

solve for t' and thus for time