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Lawrence, Ernest Orlando

particles spiral nuclear cyclotron

(1901–58) US physicist: invented the cyclotron and produced new radioactive elements.

Lawrence’s father was head of a teacher’s college and his mother had taught mathematics. The boy grew up in South Dakota; he was tall, energetic, fond of tennis and physics, and impatient of ‘culture’ and of inactivity throughout his life. He studied at South Dakota, Minnesota and Yale and in 1928 moved to a post at the University of California at Berkeley, becoming director of the Radiation Laboratory in 1936.

From 1929 Lawrence worked to produce sufficiently energetic particles for nuclear reactions, having noted suggestion that stars may be ‘powered’ by nuclear reactions. Linear accelerators for making high-energy particles were awkwardly long and used high voltages. Lawrence decided to accelerate particles on a spiral path within a pair of semi-cylinders (‘dees’) mounted in a vacuum between the poles of an electromagnet. An AC voltage at high frequency applied to the dees gave the particles their impetus. The first small cyclotron (using a 10 cm magnet) operated in 1931. Later and larger cyclotrons achieved proton beams of 8×10 4 eV, and converted lithium nuclei to helium nuclei to confirm and WALTON’S first nuclear transformation (1932). Hundreds of new radioactive isotopes were eventually produced, including most of the transuranium elements; Lawrence investigated their use in medicine. Mesons and antiparticles were generated and studied, with Lawrence coordinating the efforts of a team. Lawrencium (Lr, atomic number 103) was named for him, and he received the 1939 Nobel Prize for physics. In 1940 his team isolated plutonium and neptunium, and he contributed to the development of the atomic bomb.

Lawrence’s cyclotron. The oscillator reverses the PD between the dees several million times per second. Positive ions (eg protons, H+) are released at the centre and are accelerated into nearly circular paths until they emerge with a high energy. The spiral path is actually many kilometres long; ie the spiral is ‘tightly wound’.

Lawrence, Martin (1965–) [next] [back] Lawes, Sir John Bennet

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