Question

If the half-life of iodine-131 is 8 days, how much of a 5-g sample is left after 32 days?

Answer 1

`0.3125\`g

Explanation:

The half life `T_{\text{1/2}}` is the period of time after which the amount of radioactive element becomes half of its original amount

The amount left `N` after `n` half lives of a radioactive element with original amount `N_0` is

`N=N_0(1/2)^n`

Given that half life of Iodine-131 is `8` days hence the amount left `N` after 32 days i.e. `n=32/8=4` half lives taking initial amount `N_0=5`g

`N=5(1/2)^4=5/16=0.3125\`g