Discuss the alpha decay process with example.

Explanation

(i) When unstable nuclei decay by emitting an `alpha` - particle (`""_(2)^(4)He` nucleus), it loses two protons and two neutrons. As a result, its atomic number Z decreases by 2, the mass number decreases by 4. We write the alpha decay process symbolically in the following way
`""_(Z)^(A)Xto""_(Z-2)^(A-4)Y+""_(2)^(4)He`
(ii) Here X is called the parent nucleus and Y is called the daughter nucleus.
Ex : Decay of Uranium `""_(92)^(238)U` to thorium `""_(90)^(234)Th` with the emission of `""_(2)^(4)He` nucleus (`alpha`-particle)
`""_(92)^(238)Uto""_(90)^(234)Th+""_(2)^(4)He`
(iii) The total mass of the daughter nucleus and `""_(2)^(4)He` nucleus is always less than that of the parent nucleus. The difference in mass `(Deltam=m_(X)-m_(Y)-m_(a))` is released as energy called disintegration energy Q and is given by `Q=(m_(X)-m_(Y)-m_(a))C^(2)`
(iv) In alpha decay process, the disintegration energy is certainly positive `(Qgt0)`. In fact, the disintegration energy Q is also the net kinetic energy gained in the decay process or if the parent nucleus is at rest, Q is the total kinetic energy of daughter nucleus and the `""_(2)^(4)He` nucleus.
(v) Suppose `Qlt0`, then the decay process cannot occur spontaneously and energy must be supplied to induce the decay.