## Question

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 safety with this source is

### Solution

12 h

The radioactivity of a sample decreases to in *n* half lives. Since the initial activity is 64 times the permissible level, it must become of its initial value.

In other words in six half-lives the activity will reduce itself to the permissible level. Since half life is 2 hours, the total time taken

= 12 hours.

#### SIMILAR QUESTIONS

How much energy is released when one amu is wholly converted into energy?

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,

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