DISCOVERY OF NEUTRON
After the discovery of electron and proton Rutherford (1920) had predicted the existence of a neutral fundamental particle. In 1932, Chadwick bombarded the element Beryllium with a-particles and noticed the emission of a radiation having the following characteristics.
The radiation was highly penetrating.
The radiation was unaffected by magnetic and electric fields which show that it is electrically neutral.
It was found to have approximately the same mass as the protons.
The name ‘neutron’ was given to this sub-atomic particle. It is denoted by n or 1on. Bombardment of beryllium by α-particles results in the formation of carbon and neutrons are emitted.
Be — — → C + 1 n
At present there are a number of evidences which confirm that like electron, proton and neutron is also a fundamental constituent of atoms (a single exception is 11H atom which does not contain any neutron)
Mass of a neutron is 1.008930 amu (1.6753 x 10–24g or 1.6753 x 10–27 kg)
Neutron “A sub-atomic particle, which is a fundamental constituent of matter having mass approximately equal to the hydrogen atom and which is electrically neutral, is called a neutron”.
Illustration:-The neutron is attracted towards
(A) Positive charged particles
(B) Negative charged particles
(C) Not attracted by any charge
(D) None of these
Solution: Neutron is an uncharged particle. Hence (C) is correct.