Recent advances in nuclear physics

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The lecture on which this article is based was mainly concerned with recent advances in high energy nuclear physics. The synchro-cyclotrons built since the war are enabling studies to be made on the interaction of high-speed nucleons with nuclear matter and on the interaction of individual nucleons. This interaction is related to nuclear forces and in a way not yet understood. The interaction of nucleons produces π-mesons in large quantities and the interaction of these mesons and their decay product the μ-meson with nuclei is now producing important new information. The production of π-mesons by the photonuclear effect has now been studied at energies up to about 350 MeV. The frontiers of nuclear physics now merge with cosmic ray physics. Cosmic ray workers have discovered heavier mesons, T, Z, K and V, and some of these are produced by nucleons of energies of the order of 5 BeV. The Brookhaven proton synchrotron now produces protons of 2.3 BeV energy and a new strong focusing principle seems to make feasible machines for energies up to 100 BeV. Cosmic ray studies extend, however, out to energies of the order of 1017 eV.