What is Radioactive Disintegration? and Explain the theory of radioactive disintegration.

Radioactive Disintegration: 

When an unstable radioactive element constantly breaks up into new radioactive atoms with the emission of either 𝛼-particles or 𝛽- particles and some times with the 𝛾-rays. The new atoms in general radioactive and have entire new chemical and radioactive properties. The spontaneous breaking up of a nucleus is known as radioactive disintegration. The atoms of radioactive substance undergo continuous decay. Hence a series of a new radioactive elements is produced by disintegration until a stable element is obtained. When a radioactive element disintegrates by emission of 𝛼 rays it is turned into new element of atomic number two less and atomic weight four less than of the parent element. Similarly, when an element disintegrates by the emission of 𝛽-rays, it is tuned into another new element of atomic number one greater than that of the parent element but of the same atomic weight. The disintegration of Uranium into Thorium by emission of alpha particle and then to protactinium by the emission of beta particle is expressed as follows:

₉₂U²³⁸  → ₉₀Th²³⁴ + ₂He

( Uranium) (Thorium) ( 𝛼-particle)

₉₀Th²³⁴ → ₉₁Pa²³⁴ + _-1 𝛽⁰

(Thorium) (Protactinium) (beta Particle)

This process of disintegration continues till the stable lead nucleus forms at the end.

Rutherford-Soddy Theory of Radioactive Disintegration :

Rutherford and Soddy, in 1903, postulated that radioactivity is a nuclear phenomenon and all the radioactive changes are taking place in the nucleus of the atom. They presented an interpretation of the radioactive processes and the origin of radiations in the form of a theory known as theory of radioactive disintegration. The main points of this theory are,

1. The atomic nuclei of the radioactive elements are unstable and liable to disintegrate any moment.
2. The disintegration is spontaneous, i.e., constantly breaking. The rate of breaking is not affected by external factors like temperature, pressure, chemical combination etc.
3. During disintegration, atoms of new elements called daughter elements having different physical and chemical properties than the parent elements come into existence.
4. During disintegration, either alpha or beta particles are emitted from the nucleus.

The disintegration process may proceed in one of the following three ways,

(i) a-particle emission:When an a-particle  is emitted from the nucleus of an atom of the parent element, the nucleus of the new element, called daughter element possesses atomic mass or atomic mass number less by four units and nuclear charge or atomic number less by 2 units because a-particle has mass of 4 units and nuclear charge of two units.

Parent element   → Daughter elememt
Atomic mass : W                                               W – 4
Atomic number : Z                                             Z - 3

(ii) b-particle emission:b-particle is merely an electron which has negligible mass. Whenever a beta particle is emitted from the nucleus of a radioactive atom, the nucleus of the new element formed possesses the same atomic mass but nuclear charge or atomic number is increased by 1 unit than the parent element. Beta particle emission is due to the result of decay of neutron into proton and electron. ₀n¹ →  ₁p¹  +  _-1e⁰

           The electron produced escapes as a beta-particle-leaving proton in the nucleus.

Parent element   → Daughter elememt
Atomic mass : W                                               W
Atomic number : Z                                             Z + 1

(iii) g-ray emission: g-rays are emitted due to secondary effects. The excess of energy is released in the form of g-rays. Thus g-rays arise from energy re-arrangements in the nucleus. As g-rays are short wavelength electromagnetic radiations with no charge and no mass, their emission from a radioactive element does not produce new element.