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#15 | Solved Problems Set 8
(Physics) > Nuclei

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In a radioactive substance at t = 0, the number of atoms is 8×104, its half-life period is 3 yr. The number of atoms equal to 1×104 will remain after an interval of:

1. 9 yr

2. 8 yr 

3. 6 yr 

4. 24 yr

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PMT - 2010
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The half-life of radium is 1622 years. How long will it take for seven-eighth of a given amount of radium to decay

1. 3244 years

2. 6488 years

3. 4866 years

4. 811 years

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PMT - 1999
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In a radioactive sample the fraction of initial number of radioactive nuclei, which remains undecayed after n mean lives is:

1. 1en 

2.  en   

3. 1-1en 

4. 1e-1n

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The activity of a radioactive sample is measured as 9750 counts/min at t = 0 and as 975 counts/min at t = 5 min. The decay constant is approximately:

1. 0.922/min           

2. 0.691/min         

3. 0.461/min           

4. 0.230/min

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The half-life period of a radioactive substance is 6 h.  If after 24 h, activity is 0.01 μCi, what was the initial activity? 

1. 0.04 μCi 

2. 0.08 μCi

3. 0.24 μCi 

4. 0.16 μCi

 67%
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