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%
From NCERT
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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%
From NCERT
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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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If a radioactive nucleus decays according to the following reaction

X18072αX1βX2αX3γX4

then the mass number and the atomic number of X4 then the mass number and the atomic number of X4 will be, respectively 

1. 172, 70 

2. 172, 69

3. 172, 68

4. 171, 69

Subtopic:  Types of Decay |
 86%
From NCERT
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