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

Options

A. 4860
B. 2430
C. 3240
D. 1080

Answer

D

Explanation

(d) `lamda = lamda_1 + lamda_2`
`rArr (1)/(T) = (1)/(T_1) +(1)/(T_2)`
`:. T = (T_1 xx T_2)/(T_1 + T_2) = (810 xx 1620)/(810 + 1620) = 540 years`
Hence, `(1)/(4) th` of material remain after `1080 years`.