A free neutron decays into a proton, an electron and:

1. A beta particle.

2. An alpha particle.

3. An antineutrino.

4. A neutrino.

Subtopic:  Types of Decay |
 64%
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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

Subtopic:  Radioactivity (OLD NCERT) |
 54%
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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

Subtopic:  Radioactivity (OLD NCERT) |
 54%
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The energy equivalent of one atomic mass unit is:

1. 1.6×10-19 J 

2. 6.02×1023 J

3. 931 MeV 

4. 9.31 MeV

Subtopic:  Mass-Energy Equivalent |
 83%
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Solar energy is due to:

1. fusion reaction.

2. fission reaction.

3. combustion reaction.

4. chemical reaction.

Subtopic:  Nuclear Energy |
 67%
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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) |
 52%
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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 |
 68%
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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) |
 67%
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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 |
 89%
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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 |
 66%
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