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

Subtopic:  Radioactivity (OLD NCERT) |
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The energy equivalent of one atomic mass unit is:
1. \(1.6\times 10^{-19}~\text{J}\)
2. \(6.02\times 10^{23}~\text{J}\)
3. \(931~\text{MeV}\)
4. \(9.31~\text{MeV}\)

Subtopic:  Mass-Energy Equivalent |
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Solar energy is due to:

1. fusion reaction. 2. fission reaction.
3. combustion reaction. 4. chemical reaction.
Subtopic:  Nuclear Energy |
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At time t = 0, N1 nuclei of decay constant λ1 and N2 nuclei of decay constant λ2 are mixed. The decay rate of the mixture is:

1. -N1N2e-λ1+λ2t 

2. -N1N2 e-λ1+λ2t 

3. -N1λ1e-λ1t + N2λ2e-λ2t 

4. -N1λ1N2λ2e-λ1+λ2t

Subtopic:  Radioactivity (OLD NCERT) |
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A nucleus Xnm emits one α and two β-particles. The resulting nucleus is

1. Xnm-4 

2. Xn-2m-4   

3. Xn-4m-4 

4. None of these

Subtopic:  Types of Decay |
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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

Subtopic:  Radioactivity (OLD NCERT) |
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The radius of a nucleus of a mass number A is directly proportional to [MH CET 1999; AMU (En.) 2001; UPSEAT 2004; DUMET 2010]

1. A3 

2. A 

3. A2/3

4. A1/3

Subtopic:  Nuclear Binding Energy |
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mP and mn are masses of proton and neutron respectively. An element of mass m has Z protons and N neutrons, then 

1. m>Zmp+Nmn

2. m=Zmp+Nmn

3. m<Zmp+Nmn

4. m may be greater than, less than or equal to Zmp+Nmn, depending on the nature of the element.

Subtopic:  Mass-Energy Equivalent |
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The nuclei C136 and N147 can be described as [1990]

1. isotones

2. isobars 

3. isotopes of carbon

4. isotopes of nitrogen

Subtopic:  Mass-Energy Equivalent |
 88%
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The radioactivity of a sample is A1 at a time t1 and A2 at time t2.  If the mean life of the specimen is T, the number of atoms that have disintegrated in the time interval of t2-t1 is:

1. A1-A2 

2. A1-A2T

3. A1-A2T

4. A1t1-A2t2

Subtopic:  Radioactivity (OLD NCERT) |
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