The half-life of radium is 1600 yr.  The fraction of a sample of radium that would remain

after 6400 yr [1991]

1. 14   

2. 12 

3. 18 

4. 116

Subtopic:  Radioactivity (OLD NCERT) |
 80%
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The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life 30 min decreases to 5 s-1 after 2 h. The initial count rate was [1995]

1. 20 s-1 

2. 25 s-1 

3. 80 s-1 

4. 625 s-1

Subtopic:  Radioactivity (OLD NCERT) |
 69%
From NCERT
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An element \(A\) decays into element \(C\) by a two-step process
\(A\rightarrow B+_{2}^{4}\mathrm{He}\)
\(B\rightarrow C+2e^{-}\)
Then: 
1. \(A\) and \(C\) are isotopes
2. \(A\) and \(C\) are isobars
3. \(A\) and \(B\) are isotopes
4. \(A\) and \(B\) are isobars
Subtopic:  Types of Decay |
 66%
From NCERT
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The radius R of a nuclear matter varies with A as

1. R α A2/3

2. R α A1/3

3. R α A0 

4. R α A

Subtopic:  Mass-Energy Equivalent |
 95%
From NCERT
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Number of nuclei of a radioactive substance at time t = 0 are 2000 and 1800 at time t = 2s. Number of nuclei left after t = 6s is [MGIMS 2010]

1. 1442 

2. 1554 

3. 1652 

4. 1458

Subtopic:  Radioactivity (OLD NCERT) |
 61%
From NCERT
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In a radioactive material, the activity at time t1 is R1 and at a later time, t2 is R2. If the decay constant of the material is λ, then:

1. R1=R2e-λt1-t2   

2. R1=R2eλt1-t2

3. R1=R2t2t1 

4. R1=R2

Subtopic:  Radioactivity (OLD NCERT) |
 73%
From NCERT
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Which of the following are suitable for the fusion process ? [2002]

1. Light nuclei

2. Heavy nuclei

3. Elements lying in the middle of periodic table

4. Elements lying in the middle of binding energy curve

Subtopic:  Nuclear Binding Energy | Radioactivity (OLD NCERT) |
 78%
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An archeologist analyses the wood in a prehistoric structure and finds that C14 (Half - life=5700 years) to C12 is only one - fourth of that found in the cells buried plants. The age of the wood is about

1. 5700 yr

2. 2850 yr

3. 11,400 yr

4. 22,800 yr

 

Subtopic:  Radioactivity (OLD NCERT) |
 81%
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In the nuclear reaction: \(\mathrm{X}\left(n,\alpha\right){}_{3}^{7}\mathrm{Li}\) the term \(\mathrm{X}\) will be:

1. \({}_{5}^{10}\mathrm{B}\) 2. \({}_{5}^{9}\mathrm{B}\)
3. \({}_{5}^{11}\mathrm{B}\) 4. \({}_{2}^{4}\mathrm{He}\)
Subtopic:  Types of Decay |
From NCERT
PMT - 2001
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10 g of radioactive material of half-life 15 year is kept in store for 20 years. The disintegrated material mass is [Pb. PMT 2002]

1. 12.5 g

2. 10.5 g

3. 6.03 g

4. 4.03 g

Subtopic:  Radioactivity (OLD NCERT) |
 57%
From NCERT
PMT - 2002
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