Particles carrying positive charge i.e. canal rays was discovered by electrical discharge carried out in the modified cathode ray tube.

(i) The positively charged particles depend upon the nature of gas present in the cathode ray tube. These are positively charged gaseous ions.

(ii) The charge to mass ratio of the particles is dependent on the gas from which these originate.

(iii) Some of the positively charged particles carry the multiple of the fundamental electrical charge unit.

(iv) These particles in the magnetic or electrical field behave opposite to the cathode rays or electron.


The smallest and lightest positive ion was obtained from hydrogen and was given the name proton by Rutherford.

After the discovery of electron and proton, need of a electrically neutral particle was felt. These particles were discovered by Chadwick(1932).

When a thin sheet of beryllium was bombarded by `alpha`-particles, electrically neutral particles having greater mass than that of the protons was emitted. These are called neutrons.

`text()_4^9(Be) + text()_2^4(He) -> text()_6^12(C) + text()_0^1 n`

See Table 2.1.