Question

The mean life of a radio active material for "a" and $"\beta "$ decay are 1620 years and 520 years. The half life of the sample is nearly

• A. 490 years
• B. 126 years
• C. 273 years
• D. 888 years

Answer 1

The correct option is C 273 years

Given : ${\tau }_a=1620years$ ${\tau }_b=520years$

Mean life of the sample $\tau =\frac{{\tau }_a\times {\tau }_b}{{\tau }_a+{\tau }_b}$

So, $\tau =\frac{1620\times 520}{1620+520}=393.6years$

Half life $T=\frac{\tau }{11.44}=\frac{393.6}{1.44}=273years$