Question

How long will it take for a 40.0 gram sample of I-131 (half life = 8.040 days) to decay to 1/100 its original mass?
Expert's answer

Answer 1

The general formula is

$t=\frac{t_{1/2}ln(\frac{N_t}{N_0})}{-ln2}$ , where $N_t$ is the amount of the substance at given time, $N_0$ is the initial amount, $t$ is the time and $t_{1/2}$ is the half life.

Therefore,

$t=\frac{8.040days\times{ln\frac{1}{100}} }{-0.693}=53.4days$

Answer: 53.4 days