Neutron

The neutron as a distinct, separate particle was discovered in l932 by a British physicist, James Chadwick (1891-1974). He was using radiation emitted from radioactive radium to bombard various materials. When he irradiated the element beryllium, he found that a very penetrating particle was produced. It could go through an inch thickness of lead. Chadwick reasoned that the new particle must be electrically neutral, because all other radiation known at that time would have been stopped by the lead. Chadwick was awarded the 1935 Nobel Prize in physics for his discovery.