Briefly explain the discovery of neutrons and how it can be demonstrated.

(N/A) In $1932$,James Chadwick verified the hypothesis that the atomic nucleus contains neutral particles in addition to protons.
Chadwick observed the emission of neutral radiation when beryllium nuclei were bombarded with $\alpha$-particles.
He further observed that this neutral radiation could knock out protons from light nuclei,such as those of helium,carbon,and nitrogen.
The only neutral radiation known at that time was photons (electromagnetic radiation).
Application of the principles of conservation of energy and momentum showed that if the neutral radiation consisted of photons,their energy would have to be much higher than what is available from the bombardment of beryllium nuclei with $\alpha$-particles.
Chadwick satisfactorily resolved this by assuming that the neutral radiation consists of a new type of neutral particle called neutrons.
Using the conservation of energy and momentum,he determined the mass of the new particle (neutron) to be very nearly the same as the mass of a proton.
Currently,the mass of a neutron is precisely $m_{n} = 1.00866 \ u = 1.6749 \times 10^{-27} \ kg$.
Chadwick was awarded the $1935$ Nobel Prize in Physics for his discovery of the neutron.