Elementary Particles

By the year 1932, the view of the structure of matter had reached a simple form. The atomic nucleus was thought to contain protons and some electrons. Electrons served to neutralize the electric charges of some of the protons. (This is because excepting ordinary hydrogen, the atomic weight of an element always exceeds its atomic number which tells the electric charge of the nucleus). Beta radiation, where an electron is fired out of the nucleus, supported the view of the electron as a part of the nucleus. All matter was made of two units, elementary particles: the light negatively charged electron and the heavy positive proton. By combining these, one may assemble the nuclei of all elements. By adding suitable number of electrons to circle around the nucleus, one obtains all elements. By chemical bonding one may make all matter out of the elements, in all its different forms.

This simple picture collapsed in the “crazy” year of physics, 1932. The first major event of the year was the discovery of a new elementary particle, the neutron. The main honor for this goes to James Chadwick (1891–1974). He was a student of Rutherford in Manchester and was vice director of the Cavendish Laboratory during that year.