Question 161: Atoms & Nuclei

Question

The half life period of a radioactive substance is 60 days. The time taken for $\frac{7}{8}$th of its original mass to disintegrate will be :

Accepted Answer

$\because$ $N = {{{N_0}} \over {{2^{{t \over {{T_{1/2}}}}}}}}$
$ \Rightarrow {2^{{t \over {{T_{1/2}}}}}} = {{{N_0}} \over N} = {{{N_0}} \over {\left( {{{{N_0}} \over 8}} ight)}}$
$ \Rightarrow {2^{{t \over {{T_{1/2}}}}}} = 8 = {2^3}$
$ \Rightarrow t = 3 	imes {T_{1/2}} = 3 	imes 60$
$ = 180$ days

Answer

120 days

Answer

130 days

Answer

180 days

Answer

20 days

Atoms & Nuclei

The half life period of a radioactive substance is 60 days. The time taken for \frac{7}{8}th of its original mass to disintegrate will be :

Choose the correct answer: