Question

A 3/4 of the original amount of radioisotope decays in 60 minutes. What is its half life?

Answer 1

1) Radioactivity follows first order kinetics.

2) K = 2.303/t .(Log ( intial conc./final conc.))

3) put values and find k.

4) half life = 0.693/k

Answer 2

Sample left = 1 - $\frac{3}{4}$

= $\frac{1}{4}$ = $\frac{1}{2^{2} }$

i.e two half lives have passed

(Example: If we assume 100g of subtance then after one half life it will become 50 and after another half life time it will become 25 i.e. after two half lives 75g of substance will be decayed i.e. 75/100 = 3/4th of original substance)

Let $t_{half}$ denote the half life of substance

Then 2.$t_{half}$ = 60 minutes

$t_{half}$ = 30 minutes