November 13, 2021   Read time 3 min
The multitalented American experimental physicist Luis W. Alvarez parlayed the concept of the liquid-hydrogen bubble chamber into an enormously powerful research instrument of modern high-energy nuclear physics.

His bubble chamber work led to the discovery of many new species of short-lived, subnuclear particles and the emergence of the quark model. Luis Walter Alvarez was born on June 13, 1911, in San Francisco, California. His father, Walter C. Alvarez, was a prominent physician. In 1925, his family moved to Rochester, Minnesota, so that his father could join the staff at the Mayo Clinic. During his high school years, Alvarez used the summers to develop his experimental skills by working as an apprentice in the Mayo Clinic’s instrument shop. He enrolled in the University of Chicago as a chemistry student, but quickly embraced physics, especially experimental physics, with an enthusiasm and passion that remained lifelong characteristics. In rapid succession, he earned his bachelor’s degree (1932), master’s degree (1934), and Ph.D. (1936) in physics.

After obtaining his doctorate, Alvarez began his long professional association with the University of California in Berkeley. Only World War II disrupted this relationship. From 1940 to 1943, Alvarez conducted special wartime radar research at the Radiation Laboratory of the Massachusetts Institute of Technology. He then joined the atomic bomb team at Los Alamos Laboratory, working in New Mexico from 1944 to 1945. During the Manhattan Project, Alvarez played a key role in the development of the first plutonium implosion weapon. He had the challenging task of developing a reliable, high-speed method of detonating the chemical high explosive used to symmetrically squeeze the bomb’s plutonium core into a supercritical mass. During the world’s first atomic bomb test (Trinity) on July 16, 1945, near Alamogordo, New Mexico, Alvarez flew overhead as a scientific observer. He was the only witness of the explosion to precisely sketch the first atomic debris cloud as part of his report. He also served as a scientific observer on board one of the escort aircraft that accompanied the Enola Gay, the B-29 bomber that dropped the first atomic weapon on Hiroshima, Japan, on August 6, 1945.

After World War II, Alvarez returned to the University of California in Berkeley, where he served as a professor of physics from 1945 until his retirement in 1978. His brilliant career as an experimental physicist involved many interesting discoveries. Of most importance here is the fact that Alvarez helped start the great elementary particle stampede (the “nuclear particle zoo”) that began in the early 1960s by developing the concept of the liquid-hydrogen bubble chamber into a large, enormously powerful research instrument of modern high-energy physics. His innovative work allowed teams of researchers at Berkeley and elsewhere to detect and identify many new species of very short lived, subnuclear particles. This opened the way to the development of the quark model in modern nuclear physics.

When an elementary particle passes through the chamber’s liquid hydrogen (kept at a temperature of −250 degrees Celsius), the cryogenic fluid is warmed to the boiling point along the track that the particle leaves. Alvarez’s device photographs and carefully computer analyzes this tiny telltale trail of bubbles. Nuclear physicists then examine these data to extract new information about whichever member of the nuclear particle zoo they have just captured. Alvarez’s large liquid-hydrogen bubble chamber came into operation in March 1959 and almost immediately led to the discovery of many interesting new elementary particles. This brilliant experimental work earned him the Nobel Prize in physics in 1968.

Just before his retirement from the University of California, Alvarez collaborated with his son, Walter (a geologist), in 1980 and proposed an extraterrestrial catastrophe theory—the “Alvarez hypothesis.” This popular hypothesis suggests that a large asteroid struck Earth some 65 million years ago, causing the mass extinction of life, including that of the dinosaurs. About a year before his death, he published a colorful account of his life in the autobiography Alvarez: Adventures of a Physicist (1987). In addition to his 1968 Nobel Prize for physics, he received numerous other awards, including the Collier Trophy in Aviation (1946) and the National Medal of Science, which was personally presented to him in 1964 by President Lyndon Johnson. Alvarez died on August 31, 1988, in Berkeley, California

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