In 1932 Chadwick discovered the neutron.
When he bombarded alpha particles on a beryllium sheet. So alpha-Particles hit directly at the beryllium sheet and eject neutrons whereby the electric charge detector remains unaffected. He observed that highly penetrating radiations were produced. These radiations were called neutrons.
(i) Neutrons carry no charge i.e. they are neutral.
(ii) They are highly penetrating.