Which scientist was responsible for discovering the neutron?
His name was James Chadwick, and the discovery, for which he won a Nobel Prize came in 1932
The neutron, because it carries zero net charge was a challenging particle to identify. The discovery was of fundamental importance because the neutron, lacking a charge, is able to penetrate the nucleus of larger atoms. This eventually would lead to the first atomic fission within a few years.
I suggest you read about him here