Question

A freshly prepared radioactive sample of half-life 1 hour emits radiations that are 128 times as intense as the permissible safe limit. The minimum time after which this sample can be safely used is –

• A. 14 hours
• B. 7 hours
• C. 128 hours
• D. 256 hours

Answer 1

Answer: (B)

7 hours

Answer 2

A.P =$\frac { 1 } { 128 }$= (n = 7)

t = n T_1/2 = 7 × 1 = 7 hr