In the decay process, $n \rightarrow p + e$ energy of electron is equal to $(\Delta m)c^{2}$ where Δm = mass defect = mass of neutron – mass of proton and electron; which is fixed. Therefore, two body decay of this type cannot explain the observed continuousenergy distribution in the b-decay of a neutron or a nucleus. Note : The simple result of this exercise was one among the several arguments advanced by W. Pauli to predict the existence of a third particle in the decay products of β-decay. The particle is known as neutrino. We now know that it is a particle of intrinsic spin $\frac{1}{2}$ (like $e^{-}, p$ or $n$), but is neutral, and either massless or having an extremely small mass (compared to electron’s mass) and which interacts very weakly with matter.The correct decay process of neutron is $n \rightarrow p + e^{-} + v$].