Question

A freshly prepared radioactive source of half life 2 hours 30 minutes emits radiation which is 64 times the permissible safe level. The minimum time, after which it would be possible to work safely with source, will be _______ hours.

Answer 1

Given here, T=150 minutes, A0=64x, where, x is the safe limit.
Using the radioactive decay law relation,
A=A0×2$^{\frac{-t}{T}}$, where, t is the minimum time in hours after which it would be possible to work safely with source.
Putting the values, we have x=64x×2$^{\frac{-t}{T}}$
∴ t=6T=6×2.5=15 hours