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

Correct option is

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

Q1

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

Q2

In the equation     

           ,  

The correct symbol for X is

Q3

The kinetic energy of a 300 K thermal neutron is

Q4

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Q5

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the energy Q released is 

Q6

What is the rest mass energy of an electron?

Q7

After two hours  of the initial amount of a certain radioactive isotope remains undecayed. The half life of the isotope is  

Q8

The half life of a certain radio isotope is 10 minutes. The number of radioactive nuclei at a given instant of time is 108. Then the number of radioactive nuclei left 5 minutes later would be

Q9

The half life of Pa – 218 is 3 minutes. What mass of a 16 g sample of Pa – 218 will remain after 15 minutes?

Q10

The decay constant of a radioactive sample is . The half-life and mean-life of the sample are (respectively) given by :