Discuss the alpha decay process with example.

Explanation

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)"X" to ""_(Z-2)^(A-4)"Y" + ""_(2)^(4)"He"`.
Here X is called the parent nucleus and Y is called the daughter nucleus.
Example : Decay of Uranium `""_(92)^(238)"U"` to thorium `""_(90)^(234)"Th"` with the emission of (`alpha ` - particle)
`""_(92)^(238)"U" to ""_(90)^(234)"Th" + ""_(2)^(4)"He"`.
As already mentioned, 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 `(Delta m = m_(x) - m_(y) - m_(alpha))` is released as energy called disintegration energy Q and is given by
`Q = (m_(x) - m_(y) - m_(alpha))c^(2)`
Note tha for spontaneous decay(natural radioactivity) `Q gt 0`. In alpha decay process, the disintegration energy is certainly positive`(Q gt 0)`. 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. Suppose `Q lt 0`,then the decay process cannot occur spontaneously and energy must be supplied to induce the decay.