## Nuclear Physics, MCQ's

Choose the best possible answer from the options given with the question.

1. The binding energy of nucleus A is 7.7 MeV and that for nucleus B is 7.8 Me V. Which nucleus has the lager mass?

 (a) Nucleus A (b) Nucleus B (c) Less than nucleus A (d) None of these

Explanation: Binding energy is defined as the minimum energy required to separate the nucleons of a nucleus from each other. Remember the protons and neutrons present in the nucleus are collectively called nucleons. The nucleons are attracted to each other by strong nuclear force. The mass of the atomic nucleus is less than the sum of the masses of the individual nucleons of which the nucleus in formed. The missing mass is called the mass defect and is equal to the energy released during the formation of the nucleus. Mathematically,

Δ m = (Zmp + Nmn) – M

It is found that binding energy is more for heavier nuclei. In the given problem binding energy is more for nucleus B, therefore, nucleus B has larger mass.

See comprehensive question 4.

2. 2. How many neutrons are there in the nuclide Zn66.

 (a) 22 (b) 30 (c) 36 (d) 66
Explanation: Zn has 30 protons (and 30 electrons). Therefore, the number of neutrons = 66 – 30 = 36.

3. Mass equivalent of 931 MeV energy is

 (a) 6.02× 10-23 kg (b) 1.766× 10-27 kg (c)2.67× 10-28 kg (c) 6.02× 10-27 kg

Solution: Use Einstein equation to convert energy to mass. E = mc2. Put values,

931× 106 × 1.602 2× 10-19 = m × (3×108)2

⇒ m = (931 × 1.6022 × 106 ×  10-19)/(3× 108)2

⇒ m = (931 × 1.6022/9) × 106-19-16 = 1491.6482/9  × 10-29

⇒ m = 165.73 × 10-29 kg = 1.6573 × 10-27 kg

(Do you know where from the 1.6022 × 10-19 come?)

4. The energy equivalent to 1 kg matter is

 (a) 10-15 J (b)1 J (c) 10-12 J (d) 1017 J

Solution: Apply Einstein mass-energy equation

E = 1 × 3 × 3 × 1016 = 9 × 1016 = 0.9 × 1017 ≅ 1017 J

5. The radioactive nuclide 86Ra228 decays by a series of emission of three alpha particles and one beta particle. The nuclide X finally formed is

 (a) 84X220 (b)86X222 (c) 83X216 (d) 88X215

6. A radioactive substance has a half-life of four months. Three-fourth of the substance will

 a) 6 months b) 8 months c) 12 months d) 16 months

Explanation: Since Half of the original amount will decay in 4 months. In the next 4 months, half of the remaining half will decay. Therefore, in amount decayed in 8 months Take the example; let the initial amount is 12 kg. 6 kg will decay in the first 4 months and half of the remaining, i-e, ½ of 6 = 3 kg will decay in the next 4 months. So 9 = ¾ × 12 kg will decay in 8 months.

7. Gamma radiation are emitted due to

 a. De-excitation of atom b. De-excitation of nucleus c. Excitation of atom d. Excitation of nucleus

8. Unit of decay constant is

 a) m s b) m-1 c) m d) s-1

9. Which of the following basic forces is able to provide an attraction force between two neutrons,

 a) Electrostatic and nuclear b) Electrostatic and gravitational c) Gravitational and strong nuclear d) Only nuclear force

Hint: Neutron is neutral particle and has some mass.

10. Bottom quark carries charge

 a) 2/3 e b) -2/3 e c) +1/3 e d) -1/3 e

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2. Seerat anjum

1ev=1.6022×10^-19j

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