ALVAREZ, Luis Walter

(b. 13 June 1911 in San Francisco, California; d. 1 September 1988 in Berkeley, California), experimental physicist who won the 1968 Nobel Prize for developing the liquid hydrogen bubble chamber and detecting new resonant states (short-lived subatomic particles occurring only in high-energy nuclear collisions) in particle physics.

Alvarez was one of four children born to Walter Clement Alvarez, a physician, and Harriet Skidmore (Smythe) Alvarez. He attended grammar school and the Polytechnic High School in San Francisco before his father accepted a position at the Mayo Clinic in Rochester, Minnesota. Alvarez graduated from Rochester High School in 1928. He initially attended the University of Chicago to study chemistry, but changed his major to physics, earning a B.S. in 1932, an M.S. in 1934, and a Ph.D. in 1936, all in physics. Alvarez married Geraldine Smithwick in 1937; they had two children and later divorced. On 28 December 1958 Alvarez married Janet L. Landis, with whom he had two children.

In 1936 Alvarez worked at the Ernest O. Lawrence Radiation Laboratory at the University of California, Berkeley, and except for occasional and temporary stints at other laboratories, he spent the rest of his career there. He became a professor of physics in 1945, and served in that position until 1978, when he became a professor emeritus.

In 1937 Alvarez discovered that the capture of electrons by the nucleus (K-electron capture) is a beta-decay process and, with Robert Cornog, proved that the helium 3 isotope is stable, but the hydrogen 3 isotope is radioactive. Alvarez also made important contributions to the study of the spin dependence of nuclear forces, and he helped to produce the first mercury 198 lamp, a device developed by the Bureau of Standards into its present form as the universal standard of length for that particular wavelength of light. In 1939 he and Felix Bloch made the first measurement of the magnetic moment of the neutron, a characteristic of the strength and direction of the particle's magnetic field.

From 1940 to 1943 Alvarez worked at the Massachusetts Institute of Technology in Cambridge, Massachusetts, where he developed radar systems. His team created the VIXEN radar system for the airborne detection of submarines, a phased-array radar, the ground-controlled-approach (GCA) radar that allowed aircraft to land in poor visibility, as well as microwave beacons and linear antenna arrays. Alvarez received the 1946 Collier Trophy, the U.S. government's most prestigious aviation award, for these achievements.

Alvarez also worked on the atomic bomb project with Enrico Fermi at the metallurgical laboratory at the University of Chicago from 1943 to 1944, and in the explosives division at Los Alamos, New Mexico, from 1944 to 1945 on the Hiroshima project. He developed the detonators for the plutonium bomb, and flew as a scientific observer at both the Alamogordo and Hiroshima explosions.

After the end of World War II, Alvarez returned to Berkeley and designed the Berkeley forty-foot proton linear accelerator, completing it in 1947. He also invented the tandem electrostatic accelerator and devised the microtron for accelerating electrons. In 1951 Alvarez published the first suggestion for charge exchange acceleration that led to the development of the Tandem Van de Graaff accelerator.

In 1953 Alvarez met Donald Glaser, the inventor of the bubble chamber detector for particle physics, who in 1960 would win the Nobel Prize for physics. Alvarez built a massive (72 in [183 cm]) bubble chamber, eight times the size of the Berkeley chamber, containing liquid hydrogen harnessed to a proton synchrotron that generated particles. When the particles passed through the chamber they left a trail of ions, which triggered vaporization. The vapor trails (trails of bubbles) were recorded on cameras and analyzed using automatic scanning and measuring equipment developed by Alvarez. The data from these tests were stored on punch cards and submitted for computer analysis. The study of the trails as they curved under the effect of magnetic fields provided crucial information about the nature of the particles. Alvarez received the 1968 Nobel Prize in physics for this particle research.

The bubble chamber was used to discover a large number of new, short-lived particles, including the K (the first meson resonance) and the omega meson, discoveries that were crucial in the development of the eightfold way model of elementary particles, and subsequently the theory of quarks. The number of known elementary particles rose from about 30 to more than 100 during the 1960s, and Alvarez and his team are credited with discovering about half of the new ones.

Later in his life Alvarez devoted his time to a wide array of intellectual endeavors, including the study of cosmic rays using high-altitude balloons and superconductive magnets. He used cosmic rays to assist in the search for hidden chambers in the pyramids in Egypt, and he utilized shock wave technology to reexamine the evidence from the assassination of President John F. Kennedy in 1963. These episodes are described in his autobiography, Alvarez: Adventures of a Physicist (1987).

Alvarez held patents for more than thirty inventions, mainly in electronics and optics. Among his many awards were the Medal for Merit (1947), California Scientist of the Year for his work on high-energy physics (1960), Einstein Medal for his contribution to physical sciences (1961), Pioneer Award of the AIEEE (1963), National Medal of Science for contributions to high-energy physics (1964), and Michelson Award (1965). Alvarez's valuable contributions in fundamental physics, accelerator development, and radar technology are recognized in several branches of science.

Alvarez retired in 1978, but continued to lead an active life, regularly working in the laboratory. In 1980 he proposed, with his son Walter Alvarez, that unusually high levels of iridium at the boundary between Cretaceous and Tertiary rocks indicated a major meteor impact with Earth about 65 million years ago, and suggested that this might explain the mass extinction of the dinosaurs—a plausible but debated theory. Alvarez died at the age of seventy-seven at his home in Berkeley of complications from esophageal cancer.

Alvarez's autobiography is Alvarez: Adventures of a Physicist (1987). Biographical information is also in Peter W. Trower, ed., Discovering Alvarez: Selected Works of Luis W. Alvarez, with Commentary by His Students and Colleagues (1987), and Corinn Codye, Luis W. Alvarez (1989). See also Matt S. Meier, Conchita Franco Serri, and Richard A. Garcia, eds., Notable Latino Americans: A Biographical Dictionary (1997), and Kay Porter and Marilyn Ogilvie, eds., The Biographical Dictionary of Scientists, 3rd ed., vol. 1 (2000). Obituaries are in the New York Times (2 Sept. 1988) and the Washington Post (3 Sept. 1988).

Maria Pacheco