** Ernest Rutherford's Cavendish Laboratory at Cambridge University begins nuclear experiments with a particle accelerator built by John Cockcroft and Ernest Walton.
** In April, Walton produces the first man-made fission by using protons from the accelerator to split lithium into alpha particles.
** Using an updated version of the equipment firing deuterium rather than hydrogen, Mark Oliphant discovered helium-3 and tritium, and that heavy hydrogen nuclei could be made to react with each other. This is the first direct demonstration of fusion in the lab.
** Kantrowitz and Jacobs of the NACA Langley Research Center built a toroidal magnetic bottle and heat the plasma with a 150 W radio source. Hoping to heat the plasma to millions of degrees, the system fails and they are forced to abandon their Diffusion Inhibitor. This is the first attempt to make a working fusion reactor.
** Peter Thonemann develops a detailed plan for a pinch device, but is told to do other work for his thesis.
** Hans Bethe provides detailed calculations of the proton–proton chain reaction that powers stars. This work results in a Nobel Prize for Physics.