Alvarez, Luis W. (physicist)


(1911-1988) American Experimental Physicist, Particle Physicist, Electronic Engineer

Luis W. Alvarez was an experimentalist of extraordinary scope and ability, who won the 1968 Nobel Prize in physics for his development of the hydrogen bubble chamber, which led to great advances in the discovery of high-energy unstable states of nuclear particles.

He was born in San Francisco on July 13, 1911, the son of Walter C. and Harriet Smyth Alvarez. His father was a physician and researcher in physiology; by the time he was 10, Luis could use all the tools of his father’s shop and wire up electrical circuits. Alvarez would later credit his father’s role in nurturing his scientific creativity:

He advised me to sit every few months in my reading chair for an entire evening, close my eyes and try to think of new problems to solve. I took his advice very seriously and have been glad ever since that I did.

In 1925, the family moved to Minnesota, when Walter Alvarez joined the staff of the Mayo Clinic in Rochester. Luis spent two high school summers as an apprentice in the clinic’s instrument shop.

When he enrolled at the University of Chicago, he intended to study chemistry but found himself fascinated by physics instead. He was particularly drawn to optics; his native talent was nourished by albert abraham michelson’s optical technicians. He earned his B.S., M.S., and Ph.D. in physics from the University of Chicago in 1932, 1934, and 1936, respectively. He would later describe his training at Chicago as “atrocious,” adding, however, “I could build anything out of metal or glass, and I had the enormous confidence to be expected of a Robinson Crusoe who had spent three years on a desert island.”

In 1934, he began flying, soloing with just three hours of dual instruction. Over the next 50 years, he would log more than a thousand hours as a pilot. In 1936, he married Geraldine Smith-wyck, with whom he had two children, Walter and Jean. Beginning in 1936, he spent his entire career at the University of California at Berkeley as professor of physics; there he would later become Professor Emeritus in 1978. In 1936, Ernest Lawrence, who would become a close friend, invited him to join the Berkeley Radiation Laboratory. There he spent a year immersing himself in the literature on nuclear physics and attended Lawrence’s weekly journal club—a tradition he would continue for decades in his own home.

In 1937 Alvarez gave the first experimental demonstration of the existence of the K-shell electron capture process by nuclei. Another early development was a method for producing beams of very slow neutrons, which led to investigation of neutron scattering and to the first measurement of the magnetic moment of the neutron. Just before the beginning of World War II, he discovered 3H (tritium), best known as an ingredient of thermonuclear weapons, and He3 (helium three), which became important in low-temperature physics.

During the World War II years, Alvarez played a key role in radar research and development at the Massachusetts Institute of Technology. He invented the system known as Vixen, which permitted radar-equipped aircraft to destroy surfaced German submarines. He and his group developed ground-controlled approach (GCA) radar, which allowed ordinary aircraft and pilots to land at night and in poor visibility. He also made important contributions to the microwave early warning system and the Eagle blind bombing system.

Then, after working with enricofermi at the Metallurgical Laboratory at the University of Chicago on the first nuclear reactor, Alvarez joined the Manhattan Project team at Los Alamos under j. robert oppenheimer. He made one of his most important contributions in the critical 1944-1945 period before the end of the war, when he invented capacitor-discharge bridgewire detonators. These allow the simultaneous initiation of the multiple high-explosive “lenses” required to generate the implosion system needed for the development of the plutonium version of the atomic bomb. After the war, he returned to Berkeley and designed and constructed the first operational linear accelerator. He was also deeply involved in the effort to build a large deuteron accelerator for the production of plutonium for nuclear weapons at the Lawrence Laboratory, where he was associate director of the Lawrence Radiation Laboratory in 1949-1959 and 1975-1978. At this point in his life he married his second wife, the former research assistant Janet L. Landis; they had two children, Donald and Helen.

During this period Alvarez began to concentrate on the development and use of large, liquid hydrogen bubble chambers, in order to track unstable nuclear particles. Such particles disintegrate rapidly into other particles and are so minute that they can be identified only by the tracks they leave behind them as they move. In high-energy accelerators, these particles move at near light speeds. Although the particle life span might be only 10,000th of 1 millionth of a second, the track acquires a length of several centimeters. The pattern of tracks thus becomes very complicated. Interpreting them correctly requires advanced experimental techniques. Alvarez extended the idea of the liquid helium bubble chamber invented by donald arthur glaser and developed the hydrogen bubble chamber, an invaluable instrument for this kind of investigation.

The hydrogen bubble chamber contains many hundreds of liters of liquid hydrogen reduced to a temperature of -2500°C. When the particle passes through the chamber, the liquid hydrogen is warmed to its boiling point along the particle’s track. In the particle’s wake are a trail of bubbles that can be photographed while still very small. The photos reproduce the path of the particle. Because the chamber contains only hydrogen, all reactions must occur with hydrogen nuclei, which for high-energy processes are essentially protons. This fact considerably simplifies the interpretation of the particle production and decay phenomenon. Alvarez and his group constructed a series of increasingly delicate automatic scanning and measuring instruments for transferring the information from the photographic film into a state that can be analyzed by computer. Using these newly developed hydrogen bubble chamber techniques, they were able to discover a large number of “fundamental nuclear particle resonances.” This work on particle physics with hydrogen bubble chambers garnered Alvarez the 1968 Nobel Prize in physics.

As an inventor, Alvarez was often the one who, many years after their inception, took his own ideas into production. This was true for his stabilized optical system for binoculars or cameras, invented in 1963 and produced 20 years later as a stabilizing zoom lens for shoulder-held video cameras, and for his variable-power lens, invented in 1971 and first marketed by Polaroid in 1986. He realized profits from his more than 40 patented inventions only a few years before his death in his Berkeley home on August 31, 1988.

Alvarez was a path breaker in high-energy particle physics, a consummate engineer and technologist who made vital contributions to civil and military aviation, as well as a radical thinker whose intellectual curiosity and talent for experiment continually led him in new directions. Among his more exotic ventures was the x-raying of the great pyramid of Cheops by the use of cosmic X-ray muons, which revealed that the pyramid had no hidden chamber. He was also the first person to suggest that the extinction of the dinosaurs 65 million years ago was due to a collision of a giant comet with the Earth. Alvarez’s controversial dinosaur extinction theory was later confirmed by geological observations, which discovered high levels of minerals characteristic of the comet over the surface of the Earth. This, in turn, led to the discovery of the location of the giant comet’s crater under the waters of the Yucatan peninsula.

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