Tag: nuclear structure

Questions Related to nuclear structure

The phenomenon of pair production is :

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. The production of an electron and a positron from $\gamma$ radiation

  2. Ejection of an electron from a metal surface when exposed to ultraviolet light

  3. Ejection of an electron from a nucleus

  4. Ionization of a neutral atom

Show answer
Correct Option: A
Explanation:

Pair production :
Gamma rays of sufficient energy when passing near a nucleus disappear and materialize into pair of an electron and a positron.
To have pair production, minimum energy of $\gamma$ - ray radiation is 1.02MeV.

In pair annihilation the least number of  $\gamma $- ray photons produced is :

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  1. 2

  2. 3

  3. 4

  4. 1

Show answer
Correct Option: A
Explanation:

In a pair annihilation, atleast two gamma rays must be produced. For example, when an electron encounters a positron, they annihilate to produce two gamma rays each having $0.511$ MeV energy.

The rest energy of electron or positron is

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. 0.51 MeV

  2. 1 MeV

  3. 1.02 MeV

  4. 1.5 MeV

Show answer
Correct Option: A
Explanation:

Mass of electron $ = 9.1 \times 10^{-31}  kg$

Rest mass energy $ = mc^{2}$


                               $ =\left (\dfrac{9.1\times 10^{-31}}{1.6\times10^{-27}} \times931.978\right )c^{2}$

                               $ = 0.52\  MeV$

Positronium is converted into

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. 2 Photons each of energy 0.51MeV

  2. 1 Photon of energy 1.02 MeV

  3. 2 Photons each of energy 1.02MeV

  4. 1 Photon of energy 0.51MeV

Show answer
Correct Option: A
Explanation:

Rest mass energy of a positron (as well as electron) is $0.51$ MeV.

Total rest mass energy of positron and electron is $2(0.51) = 1.02$ MeV
Thus a positron and an electron annihilate to produce two photons each of energy $0.51$ MeV. This phenomenon is known as positron-electron annihilation process.

In pair annihilation, two  $\gamma $ -ray photons are produced due to

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  1. Law of conservation of energy

  2. Law of conservation of mass

  3. Law of conservation of momentum

  4. Law of conservation of angular momentum

Show answer
Correct Option: B
Explanation:

When a particle encounters its antiparticle, they annihilate with the transformation of their mass energies into two gamma rays obeying law of conservation of mass.

To produce pair production, the minimum energy of $\gamma $-ray should be 

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. 0.15 MeV

  2. 1 MeV

  3. 1.02 MeV

  4. 1.5 MeV

Show answer
Correct Option: C
Explanation:

Minimum energy to produce pair production should be 1.02 MeV.

The energy equivalent of 1mg of mass in joule is

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. 3 x 10$^{2}$

  2. 3 x 10$^{10}$

  3. 9 x 10$^{10}$

  4. 9 x 10$^{2}$

Show answer
Correct Option: C
Explanation:

As, $m=10^{-6}\ kg$

using, $E=mc^2$
$E= 10^{-6} \ \times (3\times 10^8)^2 $
$E=9\times10^{10}J$

Which one of the following cannot be used as a moderator in a nuclear reactor?

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. Water

  2. Heavy water

  3. Molten sodium

  4. Graphite

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Correct Option: A

Which row describes the nature of $\alpha$- particles and of $\gamma$- rays

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. $\alpha$- particles : helium nuclei ; $\gamma$ rays - electromagnetic radiation

  2. $\alpha$- particles : helium nuclei ; $\gamma$ rays - electrons

  3. $\alpha$- particles : protons; $\gamma$ rays - electromagnetic radiation

  4. $\alpha$- particles : protons; $\gamma$ rays - electrons

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Correct Option: A
Explanation:
Characteristics of $\alpha$ particle
  mass= $4$ unit
  charge = $+2$ unit
The mass of Helium nuclei is $4$ unit and charge is $+2$ unit. So, it is equivalent to $\alpha $ particle .

$\gamma $- rays  is a penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei.

A scientist carries out an experiment using a sealed source which emits $\beta$ -particles. The range of the $\beta$- particles in the air is about $30cm$.
Which precaution is the most effective to protect the scientist from the radiation?

nuclear reactions nuclear structure nuclei atomic nuclei physics

  1. handling the source with long tongs

  2. keeping the temperature of the source low

  3. opening all windows in the laboratory

  4. washing his hands before leaving the laboratory

Show answer
Correct Option: A
Explanation:

Handling the source with long tongs will prevent him from the exposure of $\beta$- particles. Since the range of $\beta$-particle is only $30cm$ so, long tongs can easily be a safer and effective precaution.