Question

One milligram of thorium emits 22 α particle per unit solid angle per minute. The half life of thorium is of the order of 

(1) ~ 100 years 

(2) ~ 1000 years 

(3) ~ 10000 years

(4) ~ 10¹⁰ years

Answer 1

Correct option : (4) ~ 10¹⁰ years

Explanation:

Number of α particle per sec in all direction is given by

No. of atoms in 1 milligram of thorium