Emission of a, b and g Rays

Emission of a and b-rays bring some changes in the nucleus of the atom and the new element formed as a result of these charges is called daughter element.

There is conservation of both atomic number and mass number in the equation of a nuclear reaction. Thus,

i) Sum of the mass numbers of various reactant species must be equal to the sum of the mass numbers of the product species.

ii) Sum of the charge numbers (atomic numbers) of reactant species and that of the product species must be equal.

Emission of a - rays

When a nucleus emits an a - particle its atomic number is reduced by two units and its mass number is reduced by four units. The daughter element, thus formed occupies a position in the periodic table two places left of the parent element. For e.g., the emission of a - particle from produces a thorium nucleus . This nuclear change is represented as

Emission of b - rays

The b - particles are electrons _-1e⁰ with mass number zero and charge equal to -1. Since nucleus does not contain electrons, the emission of b - particle from a radioactive nucleus is believed to arise from the conversion of a neutron into proton and electron.

When a b - particle is emitted, the proton formed is retained by the nucleus. Thus the daughter element so formed has atomic number one more than the parent element. There is, however, no change in its mass number. Thus the daughter element occupies a position in the periodic table one place right to the parent element.

The emission of a b - particle by thorium is represented thus

Emission of g - rays

The emission of g - rays does not produce any change either in mass number or in the atomic number of the nucleus. Emission of g - rays is observed in virtually all nuclear reactions from the nuclei, which are left in excited state by an earlier emission of a or b - particle causing a decrease in the energy of the nuclide.