The half-life of a radioactive substance is  30 minutes. The time (in minute) taken between 40% decay and 85% decay of the same radioactive substance is

(a) 15           (b) 30

(c) 45           (d) 60

Concept Questions :-

Radioactivity
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If radius of the 13Al27 nucleus is taken to be RAl then the radiusof 53Te125 nucleus is nearly-

(a)(53/13)1/3 RAl

(b)5/3 RAl

(c)3/5 RAl

(d)(13/53)1/3RAl

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A nucleus of uranium decays at rest into nuclei of thorium and helium. Then,

(a) the helium nucleus has more kinetic energy than the thorium nucleus

(b) the helium nucleus has less momentum than the thorium nucleus

(c) the helium nucleus has more momentum than the thorium nucleus

(d) the heium nucleus has less kinetic energy than the thonum nucleus

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The binding energy per nucleon of  Li37 and He24 nuclei are 5.60meV and 7.06meV, respectively. 
In the nuclear reaction Li37  + H11  He24 + He24 + Q  , the value of energy Q released is -

(a)19.6MeV

(b)-2.4MeV

(c)8.4MeV

(d)17.3MeV

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A radioisotope X with a half-life 1.4x109 yr decays of Y which is stable. A sample of the rock from a cave was found to contain X and Y in the ratio 1:7. The age of the rock is

(a)1.96x109 yr

(b)3.92x109 yr

(c)4.20x109 yr

(d)8.40x10yr

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The half-life of a radioactive isotope X is 20 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio 1:7 in a sample of a given rock. The age of the rock is estimated to be

(a) 40 yr

(b) 60 yr

(c) 80 yr

(d) 100 yr

Concept Questions :-

Radioactivity
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A certain mass of hydrogen is changed to helium by the process of fusion. The mass defect in fusion reaction is 0.02866 u. The energy liberated per nucelon is (given 1 u = 931 MeV)

(a) 2.67 MeV

(b) 26.7 MeV

(c) 6.675 MeV

(d) 13.35 MeV

Concept Questions :-

Mass-energy equivalent
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If the nuclear radius of A27l is 3.6 Fermi, the approximate nuclear radius of C64u in Fermi is

(a)2.4                                         (b)1.2

(c)4.8                                         (d)3.6

Concept Questions :-

Mass-energy equivalent
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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

Concept Questions :-

Radioactivity
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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

(a) 30 days

(b) 50 days

(c) 60 days

(d) 15 days

Concept Questions :-

Radioactivity
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