Half-life of a radioactive substance is 20 min. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately-

(1) 10 min            (2) 20 min            (3) 30 min            (4) 40  min

The binding energy per nucleon is maximum in case of 

1. ${}_{2}H{e}^4$                                         

2. ${}_{26}F{e}^{56}$

3. ${}_{56}B{a}^{141}$                                     

4. ${}_{92}U_{235}$

In nuclear fission process, energy is released because [2001]

(1) mass of products is more than mass of nucleus.

(2) total binding energy of products formed due to nuclear fission is more than that the parent fissionable material.

(3) total binding energy of products formed due to nuclear fission is less than parent fissionable material.

(4) mass of some particles is converted into energy.

The mass number of helium is 4 and that for suphur is 32. The radius of sulphur nuclei is larger than that of helium by

1.  $\sqrt{8}$

2.  4

3.  2

4.  8

A freshly prepared radioactive source of half-life 2 hrs. emits radiations of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with the source is

1.  6 hrs.

2.  12 hrs.

3.  24 hrs.

4.  128 hrs.  

$\mathrm{If} \mathrm{the} \mathrm{binding} \mathrm{energy} \mathrm{per} \mathrm{nucleon} \mathrm{in} {}_3\mathrm{Li}_7 \mathrm{and} {}_2\mathrm{He}_4 \mathrm{nuclei} \mathrm{are} \mathrm{respectively} 5.60 \mathrm{MeV} \mathrm{and}$
$7.06 \mathrm{MeV}, \mathrm{then} \mathrm{the} \mathrm{energy} \mathrm{of} \mathrm{proton} \mathrm{in} \mathrm{the} \mathrm{reaction} {}_2\mathrm{Li}_7 + \mathrm{p} \to 2_2{\mathrm{He}}^4 \mathrm{is} :$

1.  19.6 MeV

2.  2.4 MeV

3.  8.4 MeV

4.  17.3 MeV

$\mathrm{In} \mathrm{the} \mathrm{equation} {}_{13}{}^{27}\mathrm{AI} + {}_2{}^4\mathrm{He} \to {}_{15}{}^{30}\mathrm{P} + \mathrm{X} \mathrm{where} \mathrm{X} \mathrm{is}-$

1.  ${}_1{}^1\mathrm{P}$

2.  ${}_1{}^2\mathrm{H}$

3.  ${}_2{}^4\mathrm{He}$

4.  ${}_0{}^1\mathrm{n}$

If the nuclear radius of ${}_{27}Al$ is 3.6 Fermi, the approximate nuclear radius of ${}_{64}Cu$ in Fermi is

1. 2.4                                       

2. 1.2

3. 4.8                                       

4. 3.6

The half-life of a radioactive isotope X is 50 yr.

It decays to another element Y which is stable.

The two elements X and Y were found to be in 

the ratio of 1:15 in a sample of a given rock.

The age of rock was estimated to be

1. 200 yr

2. 250 yr

3. 100 yr

4. 150 yr

Fusion reaction takes place at a higher temperature because: