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Nuclei

Multiple Choice Questions

31.

The binding energy per nucleon of ¹⁶O is 7.97 MeV and that of ¹⁷O is 7.75 MeV. The energy in MeV required to remove a neutron from ¹⁷O is

3.52
3.64
4.23
7.86

32.
If the ratio of the radius of a nucleus with 61 neutrons to that of helium nucleus is 3, then the atomic number of this nucleus is

27

47

51

61

The radius is directly proportional to $\frac{1}{3}$ power of mass number, i.e R ∝ A^1/3

$or \frac{A_{1}}{A_{2}} = {(\frac{R_{1}}{R_{2}})}^{3} = {(\frac{1}{3})}^{3} = \frac{1}{27} \Rightarrow \frac{A_{2}}{A_{1}} = 27 \Rightarrow A_{2} = A_{1} \times 27 = 4 \times 27 = 108 \Rightarrow Z_{2} = A_{2} - 61 = 108 - 61 = 47$

33.

A radioactive sample contains 10^-3 kg each of two nuclear species A and B with half-life 4 days and 8 days, respectively. The ratio of the amounts of A and B after period of 16 days is

1 : 2
4 : 1
1 : 4
2 : 1

34.

The binding energy per nucleon for deuteron (₁H²) and helium (₂He⁴) are 1.1 MeV and 7 .0 MeV, respectively. The energy released when two deuterons fuse to form a helium nucleus is

36.2 MeV
23.6 MeV
47.2 MeV
11.8 MeV

35.

In a series of radioactive decays, if a nucleus of mass number 180 and atomic number 72 decays into another nucleus of mass number 172 and atomic number 69, then the number of α and β particles released respectively are

36.

The half-life of a radioactive substance is 20 min. The time taken between 50 % decay and 87.5 % decay of the substance will be

20 min
30 min
40 min
25 min

37.

The ratio of the surface area of the nuclei ₅₂Te¹²⁵ to that of ₁₃Al¹²⁷ is

$\frac{5}{3}$
$\frac{125}{17}$
$\frac{1}{4}$
$\frac{25}{9}$

38.

On an average, the number of neutrons and the energy of a neutron released per fission of a uranium atom are respectively

2.5 and 2 keV
3 and 1 keV
2.5 and 2 MeV
2 and 2 keV

39.

A radioactive material of half-life time of 69.3 days kept in a container. $\frac{2}{3} rd$ of the substance remains undecayed after (given, $\ln \frac{3}{2} = 0.4$ )