If the fraction of the atoms of a radioactive material left after 120years is 1/64, what is the half-life of the material?
A
24 years
B
20 years
C
10 years
D
2 years
Verified Correct Answer: B.
Physical Principles & Numerical Solution
1/64 is the usual fraction left of any radio active material after 4 half-lives, since 1/64 = (1/2)6
This implies that 6 half lives have elapsed.
Thus 6 half lives = 120 years
∴ 1 half life = 120/6 = 20 years
Source: Myschool Past Questions Archive (Record #1447)