A freshly prepared radioactive source of half life 2 hours emits radiation of intensity which is 64times the permissible level? The minimum time after which it would be possible to work safely with this source is?

Answers (1)

we know that 

Number of nuclei in terms of half life

N=\frac{N_{0}}{2^{t/t_{1/2}}}

and it is also given that N_0=64N_s

 

where N_s is corresponding to safe limit

and t_{\frac{1}{2}}=2h

so we get 

N_s=64N_se^{-\frac{ln2*t}{2}}

after solving we get t=12 hours

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