The half-life of radium is 1600 yr.  The fraction of a sample of radium that would remain

after 6400 yr [1991]

(1) 14                (2) 12                 (3) 18                   (4) 116

Concept Questions :-

Radioactivity
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The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life 30 min decreases to 5 s-1 after 2 h. The initial count rate was [1995]

(1) 20 s-1             (2) 25 s-1             (3) 80 s-1              (4) 625 s-1

Concept Questions :-

Radioactivity
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An element A decays into element C by a two step process

AB+H2e4BC+2e-

then  [1989]

(1) A and C are isotopes

(2) A and C are isobars

(3) A and B are isotopes

(4) A and B are isobars

Concept Questions :-

Types of decay
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The radius R of a nuclear matter varies with A as

(1) R α A2/3                         (2) R α A1/3

(3) R α A0                             (4) R α A

Concept Questions :-

Mass-energy equivalent
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Number of nuclei of a radioactive substance at time t = 0 are 2000 and 1800 at time t = 2s. Number of nuclei left after t = 6s is [MGIMS 2010]

(1) 1442               (2) 1554                 (3) 1652                 (4) 1458

Concept Questions :-

Radioactivity
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In a radioactive material the activity at time t1 is R1 and at a later time t2, it is R2. If the decay constant of the material is λ, then

(a) R1=R2e-λt1-t2                                    (b) R1=R2eλt1-t2

(c) R1=R2t2t1                                          (d) R1=R2

Concept Questions :-

Radioactivity
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Which of the following are suitable for the fusion process ? [2002]

(1) Light nuclei

(2) Heavy nuclei

(3) Elements lying in the middle of periodic table

(4) Elements lying in the middle of binding energy curve

Concept Questions :-

Nuclear binding energy
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An archeologist analyses the wood in a prehistoric structure and finds that C14 (Half - life=5700 years) to C12 is only one - fourth of that found in the cells buried plants. The age of the wood is about

1. 5700 yr

2. 2850 yr

3. 11,400 yr

4. 22,800 yr

 

Concept Questions :-

Radioactivity
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In the nuclear reaction: X(n, α)3Li7 the term X will be :

(1) B105                  (2) B95

(3) B115                  (4) H2e4

Concept Questions :-

Mass-energy equivalent
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10 g of radioactive material of half-life 15 year is kept in store for 20 years. The disintegrated material mass is [Pb. PMT 2002]

(1) 12.5 g               (2) 10.5 g               (3) 6.03 g              (4) 4.03 g

Concept Questions :-

Radioactivity
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