Question

A radioactive material decays by simulataneous emission of two particle from the with respective half - lives `1620` and `810` year . The time , in year , after which one - fourth of the material remains is
A. 1080
B. 2430
C. 3240
D. 4860

Answer 1

Correct Answer - A
(a) `lamda = lamda_1 + lamda_2 rArr (1)/(T) = (1)/(T_1) + (1)/(T_2)`
`:. T = (T_1 T_2)/(T_1 + T_2) = (810 xx 1620)/(810 + 1620)`
=`540 days`
Hence `(1)/(4) th` of material remain after `1080 years`.