Answer to Question #347572 in Physics for Loie

Question

How long will it take a 4.5Ci sample of material to reach an activity level of 0.14Ci if the half-life is 435 years?

Answer 1

$$A=A_02^{-t/t_{1/2}}$$

$$0.14=4.5*2^{-t/435\:\rm yrs}$$

$$t=-435*\log_2(0.14/4.5)=2178\:\rm yrs$$