CPB Ljubljana 2018 course book

Atomic Nucleus

Until 1932 physicists assumed that atomic nuclei are constructed of protons, alpha-particles and electrons.

In 1932 Sir James Chadwick (1891-1974) identified the neutron by interpreting correctly the results of the experiments carried out mainly by Jean Frédéric (1897- 1958) and Irène Joliot-Curie (1900-1956): neutrons, uncharged particles were ejected out of beryllium nuclei after their bombardment with alpha-particles. Chadwick considered neutrons to be an electron-proton compound and added it to the nuclear mix. In July 1932 Heisenberg published his neutron-proton nuclear model by assuming that neutrons and protons to be the constituents of the nucleus. His nucleus also contained electrons, nuclear electrons, bound and unbound ones. The assumption of the existence of nuclear electrons was completely rejected in the late 1930’s after the introduction of the neutrino by Pauli in 1931 and the establishment of Enrico Fermi’s (1901-1954) theory of beta-decay published in 1933.