A mixture consists of two radioactive materials A1 and A2 with half lives of 20 s and 10 s respectively.Initially the mixture has 40g of A1 and 160g of A2. The amount of the two in the mixture will become equal after

(a)60 s                                      (b)80 s

(c)20 s                                      (d) 40 s

Subtopic:  Radioactivity (OLD NCERT) |
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The half-life of a radioactive nucleus is 50 days. The time interval (t2-t1) between the time t2 when 23 of it has decayed and the time t1 when 13 of it had decayed is:

1. 30 days

2. 50 days

3. 60 days

4. 15 days

Subtopic:  Radioactivity (OLD NCERT) |
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Fusion reaction takes place at high temperature because

(1) atoms get ionised at high temperature 

(2) kinetic energy is high enough to overcome the Coulomb repulsion between nuclei

(3) molecules break up at high temperature

(4) nuclei break up at high temperature

Subtopic:  Mass-Energy Equivalent | Nuclear Energy |
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Two radioactive nuclei P and Q, in a given sample decay into a stable nucleus R. At time t=0, the number of P species are 4N0 and that of Q is N0Half-life of P(for conversion to R) is 1 min whereas that of Q is 2 min. Initially there are no nuclei of R present in the sample. When number of nuclei of P and Q are equal, the number of nuclei of R present in the sample would be: 

1. 3N0                                         

2. 9N02

3. 5N02                                       

4. 2N0

Subtopic:  Radioactivity (OLD NCERT) |
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The mass of a L37i nucleus is 0.042u less than the sum of the masses of its nucleons.The binding energy per nucleon of L37i nucleus is nearly

(a) 46 MeV                              (b) 5.6 MeV

(c) 3.9 MeV                             (d) 23 MeV

Subtopic:  Nuclear Binding Energy |
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The activity of a radioactive sample is measured as N0 counts per minute at t=0 and N0/e counts per minute at t=5 min.The time (in minute) at which the activity reduces to half its value is 

(1) loge2/5                                                         

(2) 5loge 2

(3) 5 log10 2                                                         

(4) 5 loge 2

Subtopic:  Radioactivity (OLD NCERT) |
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The decay constant of a radio isotope is λ. If A1 and A2 are its activities at times t1 and t2 respectively, the number of nuclei which have decayed during the time (t1-t2) is:

1. A1t1-A2t2                                       

2. A1-A2

3. (A1-A2)λ                                         

4. λ(A1-A2) 

Subtopic:  Radioactivity (OLD NCERT) |
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The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an

(1) isobar of parent                                   

(2) isomer of parent

(3) isotone of parent                                 

(4) isotope of parent 

Subtopic:  Types of Decay |
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Two nuclei have their mass numbers in the ratio of 1:3. The ratio of their nuclear densities would be 

(1) 1:3

(2) 3:1

(3) 31/3:1

(4) 1:1

Subtopic:  Mass-Energy Equivalent |
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The size of an atom is of the order of

(a) 10-8 m         (b) 10-10 m 
(c) 10-12 m        (d) 10-14 m

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