Question

The percent of remaining parent isotope in a radioactive decay process is 40 percent. How many half-lives have elapsed since the material was 100 percent parent atoms?

Answer 1

Answer: Between 1 and 2.

Explanation:

Half life is the amount of time taken by a radioactive material to decay to half of its original value.

$a=\frac{a_o}{2^n}$        ............(1)

where,

a = amount of reactant left after n-half lives  = 40

$a_o$ = Initial amount of the reactant  = 100

n = number of half lives

Putting in the values we get:

$40=\frac{100}{2^n}$  

$2^n=2.5$

taking log on both sides

$nlog(2)=log(2.5)$

$n=1.32$

Thus half-lives that have elapsed is between 1 and 2