Answer to Question #32056 in Atomic and Nuclear Physics for Ramachandra Naik
Why is it that only á- particles are emitted by radioactive nuclei, while protons and neutrons are not?
The reason for departure of alpha particles from the nucleus is tunneling.
The particle passes through a tunnel barrier, and is emitted from the nucleus.
The energy of alpha particles is 4-7 MeV.
Protons and neutrons are not emitted from the nucleus,because that there is Binding energy.
Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than the sum of its constituent parts — this is what keeps the system together. Often this means that energy is released upon the creation of a bound state. This definition corresponds to a positive binding energy.