A free neutron decays into a proton, an electron and 

(1) a beta particle                 (2) an alpha particle

(3) an antineutrino                (4) a neutrino

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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 energy equivalent of one atomic mass unit is [1992]

(1) 1.6×10-19 J                   (2) 6.02×1023 J

(3) 931 MeV                             (4) 9.31 MeV

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Solar energy is due to

1. fusion reaction

2. fission reaction

3. combustion reaction

4. chemical reaction

Concept Questions :-

Mass-energy equivalent
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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 mixture is

1.  -N1N2e-λ1+λ2t 

2.  -N1N2 e-λ1+λ2t 

3.  -N1λ1e-λ1t + N2λ2e-λ2t 

4.  -N1λ1N2λ2e-λ1+λ2t

Concept Questions :-

Radioactivity
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A nucleus Xmn emits one α and two β-particles. The resulting nucleus is

(1) Xm-4n         (2) Ym-4n-2           (3) Zm-4n-4            (4) None of these

Concept Questions :-

Types of decay
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The half-life period of a radioactive substance is 6 h.  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

Concept Questions :-

Radioactivity
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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

Concept Questions :-

Mass-energy equivalent
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The half life of Po218 is 3 minutes. What fraction of a 10 gram sample of Po218, will remain after 15 minutes?

(1) 132         (2) 164            (3) 125            (4) 115

Concept Questions :-

Radioactivity
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