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Question 6: Define and explain nuclear reaction?


Definition of nuclear reaction

Nuclear reaction is defined as the change in the identity or characteristics of an atomic nucleus induced by the bombardment with energetic particles. The bombarding particle may be an α particle, a γ ray, a neutron, a proton or a heavy ion. However, in all cases the bombarding particle must have enough energy to approach to the positively charged nucleus within the range of strong nuclear force.


A typical nuclear reaction involves two reacting particles; a heavy target nucleus and a light particle. It produces, in the same way, a heavier nucleus and a light particle.

Thus when a nucleus X is bombarded with some light particle ‘a’, the product nucleus Y and a light particle ‘b’ will be produced.

X + a     —–→     Y + b

Rutherford for the first time, in 1919, observed nuclear reaction by bombarding α particles on Nitrogen. He obtained Oxygen and a proton as the products.

7N14 + 2He4     —–→     8O17 + 1H1 + Q

Energy Q

  • It is equivalent to the difference of the rest masses on the left and right of the reaction.
  • Q is negative when energy is absorbed in the reaction. Such a reaction is endothermic. In such cases energy is provided by the K.E of the bombarding particle.
  • Q is positive when energy is evolved in the reaction. Such a reaction is exothermic.

Laws of conservation in nuclear reactions

The number of protons and the number of neutrons must remain conserved.

However, because of the binding energy of the nuclei, conservation of the number of nucleons does not mean the conservation of mass. Therefore, we apply the more general mass-energy principle of Einstein to the mass difference as the energy included in the reaction.

All other laws of conservation, such as conservation of momentum and conservation of charge must also hold.


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