Nuclear physicist Emilio Segrè¹ at the controls of the Lawrence 37-inch cyclotron² in Berkeley, California, the world's first major particle accelerator, June 12, 1941. Originally a 27-inch cyclotron, it was converted to a 37-inch instrument in 1936 that could accelerate deuterons³ to 8 MeV and alpha particles⁴ to 16 MeV. Weighing 77 tonnes, it was a major breakthrough of science in its time and lead the world in atomic particle energies from 1932 until 1939, opening new frontiers in nuclear research. Discoveries with this cyclotron were numerous, including radioisotopes⁵, such as iodine-131, as well as the first man-made element, technetium-99⁶ discovered by Segrè in the machine. Modified, the magnet first showed in 1941-42 that uranium-235⁷ could be separated magnetically on a large scale.
The Lawrence 37-inch cyclotron was a type of particle accelerator invented by Ernest O. Lawrence in 1932 in which charged particles accelerate outwards from the center along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention. Cyclotrons were the most powerful particle accelerator technology until the 1950s when they were superseded by the synchrotron, and are still used to produce particle beams in physics and nuclear medicine.