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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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.

Concept Questions :-

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

Concept Questions :-

Mass-energy equivalent
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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

Concept Questions :-

Radioactivity
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Three fourth of the active nuclei decay in a radioactive sample in 3/4 s. The half-life of the sample is

(1) 12 s          (2) 1 s             (3) 38 s             (4) 34 s

Concept Questions :-

Radioactivity
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What is the radius of iodine atom? (atomic no. 53, mass no. 126) [1988]

(1) 2.5×10-11 m

(2) 2.5×10-9 m

(3) 7×10-9 m

(4) 7×10-6 m

Concept Questions :-

Mass-energy equivalent
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