A freshly prepared radioactive source of half life 2 hours emits radiation of intensity which is 32 times the permissible safe level. The minimum time after which it would be possible to work safely with the source is
A
6 hours
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B
10 hours
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C
24 hours
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D
128 hours
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Solution
The correct option is B 10 hours Numberofnucleiintermsofhalflife−N=N02t/t1/2whereinVeryusefultodeterminenumberofnucleiintermsofhalflifet12=2hrInitialintensity=32AA=A02t/t1/2=>A=32A2t/2or2t/2=25t=10hrs