1.

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 isA. 6 hoursB. 12 hoursC. 24 hoursD. 128 hours

Answer» Correct Answer - B
(b) `(N)/(N_0) = ((1)/(2))^n rArr (1)/(64) = ((1)/(2))^6`
=`((1)/(2))^n rArr n = 6`
after `6` half lives intensity emitted will be safe.
`:.` Total time taken `= 6 xx 2 = 12 hrs`.


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