Goldstein observed positive rays in the anode ray experiment in 1886.
In gold foil experiment, Rutherford bombarded alpha particles on an ultrathin gold foil and then detected the scattered alpha particles on zinc sulphide (ZnS) screen. According to Rutherford’s observation,
By 1920, scientists knew that most of the mass of the atom is in the core of nucleus and this central core contains proton. However, in 1932, James Chadwick discovered that the core also contains a new uncharged particle; he called it neutron. Neutron can be defined as “A sub-atomic particle of an atom denoted by n or n0. It has no net electric charge and a mass slightly greater than that of a proton.”
In his experiment, Chadwick bombarded beryllium atom with high-energy alpha particles. He observed that some new particles are emitted which carry no charge, and the mass of this particle is same as that of proton. A neutron is usually represented as “n” and its charge is zero.
|Discoverer||Year of discovery||Charge||Mass|
|Proton||E. Rutherford||1909||+1.6×10−19 C||1.67 ×10−27 kg|
|Neutron||James Chadwick||1932||0||1.67 ×10−27 kg|
|Electron||J.J. Thomson||1897||−1.6×10−19 C||9.11 ×10−31 kg|