1932 Discovery of Neutrons by

James Chadwick(1891 - 1974)

In 1932, James Chadwick bombarded beryllium (Be) with alpha aprticles. He allowed the radiation emitted by beryllium to incident on a paraffin wax. It was found that protons were shot out form the paraffin wax. People began to look for what was in the "beryllium radiations".

Finding Neutron

Some people suggested that the radiations may be gamma radiation. However, Chadwick found that the radiation could not be gamma radiation since energy and momentum were not conserved in its production. He showed that all the observations could be explained if the radiation consisted of neutral particles of mass approximately equal to that of proton. This neutral particle was named neutron.

equation of the nuclear reaction

This discovery of neutron marked the beginning of current theories of nuclear structure. Immediately, the neutron-proton model ( the Rutherford-Bohr model) of the nucleus was adopted:

• The nucleus is made up of protons and neutrons. These are bound together by a strong nuclear force.
• Electrons and protons carry equal but opposite charges. In a neutral atom, the number of electrons is the same as the number of protons.
• Electrons orbit the nucleus at certain fixed levels called shells.

*back*

(C)1999 ThinkQuest Team 27954