Question

A freshly Prepared radioactive source of half life 2 h emits radiation of intensity which is 64 times the Permissible safe level. The minimum time after which is would be possible to work safely with this source is. 

(A) 6 h 

(B) 24 h

(C) 12 h 

(D) 36 h

Answer 1

The correct option is (C) 12 h.

Explanation:

T_(1/2) = 2 hr.

The radioactive sample decreases to (1 / 2ⁿ) in n half lives.

∵ initial activity is 64 times permissible level, it must become (1 / 64)^th of its initial value.

∴ (1 / 64) = (1 / 2ⁿ)

∴ n = 6

∴ In 6 half lives activity will reduced itself to permissible level.

Given : half life = 2hrs hence total time taken is 6 × 2 = 12 hrs.