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  4. A freshly prepared radioactive source of half life 2 hours 30 minutes emits radiation which is 64 times the permissible safe level. The minimum time, after which it would be possible to work safely with source, will be hours.

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Q. A freshly prepared radioactive source of half life 2 hours 30 minutes emits radiation which is 64 times the permissible safe level. The minimum time, after which it would be possible to work safely with source, will be ___hours.

JEE MainJEE Main 2022Nuclei

Solution:

$A = A _0 \times 2^{- t / T } $
$\frac{ A _0}{64}= A _0 \times 2^{- t / T } $
$ \therefore t =6 T =6 \times 2 \cdot 5=15$ hours