In August 1932, Carl D. Anderson found evidence for an electron with a positive charge, later called the positron. Anderson discovered the positron while using a cloud chamber to investigate cosmic rays. This work was continued by Patrick Blackett and Guiseppe P.S. Occhialini who showed that a positron was produced together with an electron, in line with an earlier theory of Paul Dirac's. According to this theory, a positron was a hole in a sea of ordinary electrons. The positron was the antimatter equivalent to the electron.
In 1932, British physicists J. D. Cockcroft and E.T.S. Walton developed a device for accelerating protons and aimed a beam of protons at a sample of lithium. One more proton joined lithium's nucleus of three protons and four neutrons, which transmuted into two atoms of helium, each with two protons and two neutrons. This was the first time anyone had transmuted one element into another artificially.
The British physicist James Chadwick bombards beryllium with helium nuclei, and finds the neutron, the second constituent of atomic nuclei along with the proton. This electrically neutral particle can be used to penetrate and probe nuclei.
Irene Joliot-Curie (daughter of Pierre & Marie Curie) & her husband Frédéric Joliot-Curie bombard aluminum with helium nuclei to make an artificial radioactive isotope, phosphorus-30. Radioactive isotopes are soon used to examine biological processes such as the uptake of iodine by the thyroid gland.
Cherenkov radiation was first observed in the early 1900's by the experiments developed by Mary and Pierre Curie when studying radioactivity emission. The nature of such a radiation, afterwards called Cherenkov radiation was unknown. Cherenkov radiation is analogous to breaking the sound barrier. A subatomic particle such as an electron, proton or one of the mesons can exceed the reduced speed that light travels at when going through glass, gases, water etc... What results is a shock wave effect. The particle gives off light that is emitted at an angle to the particle's direction of travel.
In 1935, he published a paper entitled "On the Interaction of Elementary Particles. I." (Proc. Phys.-Math. Soc. Japan, 17, p. 48), in which he proposed a new field theory of nuclear forces and predicted the existence of the meson. Encouraged by the discovery by American physicists of one type of meson in cosmic rays, in 1937, he devoted himself to the development of the meson theory, on the basis of his original idea. Since 1947 he has been working mainly on the general theory of elementary particles in connection with the concept of the "non-local" field.
µ lepton (muon) discovered by Carl Anderson and Seth Nedermeyer. Initially assumed to be Yukawa's meson but it was too penetrating.
The German chemists Otto Hahn & Fritz Strassmann detect light elements in uranium irradiated with neutrons; the Austrian physicist Lise Meitner (in flight from the Nazis) and her nephew Otto Frisch explain this result as nuclear fission.