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  • 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 it would be possible to work sa

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 it would be possible to work safely with this source is:

Option: 1

128 h


Option: 2

24 h 


Option: 3

6 h 


Option: 4

12 h 


Answers (1)

best_answer

After n number of half-life, \mathrm{N}=\mathrm{N}_0\left(\frac{1}{2}\right)^{\mathrm{n}}

1=64\left(\frac{1}{2}\right)^n \Rightarrow\left(\frac{1}{2}\right)^6=\left(\frac{1}{2}\right)^n

\mathrm{n}=6 \text { i.e., } 6 \text { half-lives }

\therefore \quad \text { Minimum time, } \mathrm{t}=6 \times 2=12 \mathrm{~h}

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