Place: United States of America
Subject: biography, physics
US physicist who won the 1968 Nobel Prize for Physics for developing the liquid-hydrogen bubble chamber and detecting new resonant states in particle physics. Discoveries made with the hydrogen bubble chamber were instrumental in the prediction of quarks. Alvarez also made many other breakthroughs in fundamental physics, accelerators, and radar, and was well known for his studies of the pyramids and suggestion that a meteor impact led to the extinction of the dinosaurs.
Alvarez was born on 13 June 1911 in San Francisco. He went to the University of Chicago to study chemistry but changed to physics and stayed there to complete a PhD. His first major discovery, with Arthur Compton, was the discovery of the ‘east-west’ effect in cosmic rays, proving them to be positive. He then moved to Ernest Lawrence's Radiation Laboratory at the University of California, Berkeley, where he spent the rest of his career. There he discovered that the capture of electrons by the nucleus of an atom is a beta-decay process, and that helium-3 is stable but hydrogen-3 (tritium) is not. Alvarez also made important contributions to the study of the spin dependence of nuclear forces and, working with Felix Bloch, measured the magnetic moment of the neutron.
During the war he moved to the Massachusetts Institute of Technology where he developed the VIXEN radar system for the airborne detection of submarines, phased-array radars, and the ground-controlled approach (GCA) radar that enabled aircraft to land in conditions of poor visibility. Alvarez received the US government's most prestigious aviation award, the Collier Trophy, for these achievements. Alvarez later worked on the atomic bomb project - with Enrico Fermi at Chicago and in the explosives division at Los Alamos - and participated in the Hiroshima mission.
After the war he returned to Berkeley and built the first practical linear accelerator (a 32-MeV proton linac) and invented the tandem electrostatic accelerator. He also devised, but never built, the microtron for accelerating electrons. During the Korean War, Alvarez and Lawrence became convinced that the USA needed to produce its own plutonium and built another accelerator to ‘breed’ plutonium. This machine was later used for nuclear physics.
In 1953 Alvarez changed direction once again when he met US nuclear physicist Donald Glaser, inventor of the bubble chamber detector for particle physics (and winner of the 1960 Nobel prize). Glaser had been using a small, 2.5-cm/1-in glass bulb full of diethyl ether. Alvarez decided to build a massive 183-cm/72-in chamber containing liquid hydrogen. His next idea was to automate the analysis of the particle tracks captured in the chamber. He also developed automatic scanning and measuring equipment whose output could be stored on punched cards and then analysed using computers. Alvarez and co-workers used the bubble chamber to discover a large number of new short-lived particles (‘resonances’) including the K (the first meson resonance) and the ω (omega) meson. These experimental findings were crucial in the development of the ‘eightfold way’ model of elementary particles, and subsequently the theory of quarks, by Murray Gell-Mann. The techniques developed by Alvarez became standard in high-energy laboratories all over the world.
In later life, Alvarez moved away from conventional physics, using cosmic rays to search for hidden chambers in the Egyptian pyramids and his knowledge of shock waves to study the Kennedy assassination. Best-known of these researches was the discovery he made with his son Walter, a geologist, of unexpectedly high concentrations of an isotope of iridium in the thin layer of clay separating Cretaceous and Tertiary rocks (the K-T boundary). Alvarez postulated that the iridium must have come from a giant meteorite impact some 65 million years ago, and that the resulting dust in the atmosphere must have so changed the climate that the dinosaurs, who lived at that time, must have become extinct. The first half of the hypothesis is now widely accepted. Alvarez died on 1 September 1988.
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