Question

Explain 

(i) alpha decay, 

(ii) Beta decay, 

(iii) gamma decay

Answer 1

(i) Alpha decay : A nuclear reaction in which an unstable parent nucleus emits an alpha particle and forms a stable daughter nucleus, is called, ‘alpha decay’. 

Eg: Decay of uranium (U²³⁸) to thorium (Th²³⁴) with the emission of an alpha particle.

₉₂U²³⁸ → ₉₀Th²³⁴ + ₂He⁴ (α – decay)

In α – decay, the parent nucleus emits an a particle and so it is clear that for the daughter nucleus, the mass number decreases by four and the atomic number decreases by two.

(ii) Beta decay : A nuclear reaction, in which an unstable parent nucleus emits a beta particle and forms a stable daughter nucleus, is called ‘beta decay’. 

Eg: Beta decay of phosphorous.

₁₅P³² → ₁₆S³² + _-1e⁰ (β - decay)

In β – decay there is no change in the mass number of the daughter nucleus but the atomic number increases by one. In a nuclear reaction, the element formed as the product nucleus is identified by the atomic number of the resulting nucleus and not by its mass number.

(iii) Gamma decay: In a γ – decay, only the energy level of the nucleus changes. The atomic number and mass number of the radioactive nucleus remain the same.