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Alvarez, Luis Walter


(b. San Francisco, California, 13 June 1911; d. Berkeley, California, 1 September 1988)

physics, particles and detectors, geophysics.

Alvarez was among the talented physicists who shaped the course of high-energy particle physics in the twentieth century. He was responsible for advances in instrumentation, organization, and application in that field, and invented scores of devices that made radar, nuclear weapons, and ground-controlled aviation feasible, as well as solving many mundane problems. His ingenuity made him a national resource in matters ranging from the Oppenheimer trial to the investigation of the Kennedy assassination. Among his greatest discoveries was a theory that accounted for the extinctions of dinosaurs and thousands of other species in the Cretaceous-Tertiary transition. He was a charismatic leader of large projects and an ingenious experimenter and inventor.

Luie, as his friends called him, was the son of the well-known physician and newspaper columnist Walter C. Alvarez, and the grandson of Luis F. Alvarez, a Spanish immigrant to the United States who was trained in medicine at Cooper Union Medical School and practiced in Hawaii. Luie’s aptitude for invention was stimulated by the mechanical and electrical instruments in his father’s laboratories at the Hooper Foundation in San Francisco and the Mayo Clinic in Rochester, Minnesota. Alvarez chose to study at the University of Chicago, where he received his BSc, MS, and PhD in physics. During his first years at Chicago, he developed a method of teaching the technique of grazing incidence spectroscopy using a broken phonograph record, a method he subsequently published in School Science and Mathematics. His first scientific paper, written with his advisor, Arthur Compton, the leading American researcher in cosmic-ray physics, reported Alvarez’s experimental verification of what came to be called the east-west effect in cosmic radiation. This was the result of the effect of the magnetic field of the earth on charged particles that make up cosmic rays. The effect had been predicted by Bruno Rossi, who replicated the discovery two months later in Eritrea.

Although he graduated in 1936, when academic jobs were difficult to find, he was asked to become a research assistant at the Radiation Laboratory of the University of California in Berkeley, which became a formal research unit in the same year. Berkeley’s Ernest Lawrence knew Luie well from his visit to the Century of Progress Exhibition in Chicago in 1933, when Lawrence spent a day impressing the young graduate student with his enthusiasm and camaraderie. Luie’s sister had been Lawrence’s secretary and his father sat on the board of the Macy Foundation, which funded Lawrence’s research. Two years after Luie’s arrival, he was appointed assistant professor in Berkeley’s physics department, and he retained his association with the university for the rest of his life.

Always a quick study, Alvarez soon mastered the literature of the field and the operation of the cyclotron, a notoriously difficult particle accelerator. He collaborated with Edwin M. McMillan in the design of the sixty-inch cyclotron and in the development of a means for extracting the beam from the cyclotron, making it unnecessary to shut it down to insert targets, thus greatly increasing the productivity of the machine in the manufacture of radioisotopes. The cut-and-try methods employed in the construction and use of the cyclotron transcended the theoretical understanding of its operation and accustomed Alvarez to the kind of bold leaps that marked the career of his mentor Lawrence. In addition, Alvarez carefully and thoroughly designed and executed his experiments with the cyclotron and prized physics before production of isotopes.

For example, in 1939 Alvarez used the newly completed Crocker medical cyclotron to discover helium-3, an important isotope of helium that, instead of the usual two protons and two neutrons, contains two protons and only one neutron. After Ernest Rutherford’s discovery of tritium in 1934 (an isotope of hydrogen containing one proton and two neutrons), Hans Bethe and others believed that tritium was stable and produced by helium-3’s radioactive decay. In setting up his experiment, Alvarez observed the acceleration of particles of mass three by tuning the radio-frequency field of the cyclotron. Because his source material was extracted from natural gas in Oklahoma, he concluded that helium-3, like its isotope helium-4, must be stable, because the deposits of gas were thousands of years old. With his graduate student Robert Cornog, he went on to find that tritium produced by deuteron bombardment of heavy water was actually radioactive.

Attracted by the work of the Fermi group, Alvarez succeeded in extracting a slow neutron beam from the cyclotron that facilitated his measurement of neutron scattering in hydrogen. With Felix Bloch, he determined the magnetic moment of the neutron, a key step in the development of nuclear magnetic resonance imaging (MRI).

Enrico Fermi’s postulation of nuclear decay through the emission of an electron afforded another avenue to knowledge of particles interacting inside the atomic nucleus, including positron emission and orbital electron capture. Gian-Carlo Wick provided theoretical insight into these processes, but it was Alvarez who first observed the capture of electrons from the innermost energy level, the K level. He accomplished this by interpreting the x-rays given off by the electrons as they were captured. Alvarez suggested to his student Phillip Abelson that Abelson might use the same techniques to determine the atomic numbers of the so-called “transuranium elements,” which Enrico Fermi had postulated would result from slow-neutron bombardment of uranium and other heavy elements, but which had defied traditional physical and chemical methods of identification.

When fission was discovered by Otto Hahn, Fritz Strassman, and Lise Meitner in late 1938, Abelson was planning to examine the x-ray spectra of elements below uranium, having failed to find any of atomic numbers exceeding the known ninety-two elements. Alvarez read of the discovery while having his hair cut in the Berkeley campus barber shop, and immediately informed Abelson, who was quickly able to duplicate the German results on neutron bombardment of uranium. Abelson and McMillan soon found evidence of elements heavier than uranium in cyclotron-bombarded uranium foils, resulting in the discovery of neptunium and of plutonium (by Glenn Seaborg working with Emilio Segrè), for which McMillan and Seaborg received the Nobel Prize in Chemistry in 1951.

Radar. A number of military agencies had sought to develop means of detecting enemy aircraft after World War I demonstrated the menace of aerial bombardment, using radio detection and ranging (radar). Because the size of the target that could be located by radio waves was proportional to their wavelengths, development pushed from shortwave radio to smaller and smaller wavelengths. The limits on this development were the magnitude of the electron tubes that generated the waves. A solution to this problem was the substitution of a solid-state device, the cavity magnetron, for the electron tube. This discovery, made by John T. Boot and Herman Randall at Marcus Oliphant’s cyclotron in Birmingham, England, made possible the development of microwave radar.

In the year after World War II began in 1939, President Franklin Delano Roosevelt approved the formation of the National Defense Research Committee (NDRC) under the leadership of Vannevar Bush, president of the Carnegie Institution, to augment military scientific

research. Alfred Lee Loomis, an amateur physicist and philanthropist who had supported Lawrence’s development of a giant cyclotron at the Radiation Laboratory in Berkeley, chaired the Microwave Committee of the NRDC. When Loomis learned of the cavity magnetron from the British, he asked committee member Lawrence to recruit a staff for a new laboratory at MIT to develop it. To cloak the effort, the name “Radiation Laboratory” was adopted. Lawrence recruited Alvarez and sent both Alvarez and McMillan to the MIT laboratory, which was headed by another cyclotron builder, Lee A. DuBridge of the University of Rochester. Alvarez took charge of expediting the development of the first successful radar sets that detected surfaced submarines as well as aircraft. He also devised a means to land aircraft under difficult conditions through Ground-Controlled Approach radar (GCA).

Nuclear Weapons. Alvarez was subsequently summoned to the Metallurgical Laboratory at the University of Chicago, where his former advisor, Arthur Compton, had centralized war work on plutonium, including Fermi’s experimental nuclear reactors (piles) from Columbia University and Seaborg’s plutonium chemistry from the University of California, over Lawrence’s vehement objections that his laboratory could do the job and Compton’s could not in a meeting Alvarez attended. Lawrence, however, continued to develop a means of separating fissile uranium-235 isotopes from uranium-238 using a modified cyclotron as a giant mass spectrometer. Although Alvarez intended to join this effort, illness delayed his transfer, and Robert Oppenheimer recruited him to work at the new Los Alamos laboratory building the atomic bomb.

Alvarez’s achievements at Los Alamos played a large part in making the implosion bomb possible. The designers thought at first to make a plutonium bomb achieve criticality through firing one fraction of a critical mass into another fraction, as was done with their uranium weapon. However, Emilio Segrè discovered that their reactor-made plutonium contained an isotope with a high probability of spontaneous fission. Thus, two separated fractions would not be stable long enough to allow the shotgun design. An alternative suggestion explored by Seth Neddermeyer and Ed McMillan, who had preceded Alvarez at Los Alamos, was implosion of a subcritical mass of plutonium by a sphere of high explosives. Working with Harvard chemist George Kistiakowsky, who developed the high-explosive lenses that focused the inward-moving wave of the high-explosive blast, Alvarez devised a system that simultaneously ignited thirty-six detonators regularly spaced on the outside of the high explosive to successfully compress the nuclear fuel to criticality. In order to determine the effectiveness of this system, Alvarez detonated spheres of highly radioactive radium-lanthanum with high explosives inside modified Army tanks; the resulting gamma-radiation showed the regularity of the implosion.

The final test of this system was made at an Army bombing range north of Alamogordo, New Mexico, in the Jornada del Muerto, which Oppenheimer had designated Trinity site. Alvarez, who had been asked to design a means of measuring the force of the blast, observed the test from a B-29 flying twenty-five miles away. He convinced Oppenheimer that he should be allowed to use the blast detectors he had created in combat. Hence, Alvarez flew with the mission that dropped the first atomic bomb—which was of the original uranium shotgun design—on Hiroshima, releasing his parachute-borne detectors from an accompanying B-29. He was thus present at the explosions of both the first uranium and the first plutonium bombs.

Alvarez returned to accelerator work at the Radiation Laboratory in Berkeley after the war. The Manhattan Engineer District provided Alvarez and his colleagues with generous funding to complete a 184-inch synchrocyclotron and an electron synchrotron based upon McMillan’s newly discovered principle of phase stability, and a proton linear accelerator designed by Alvarez based on his experience with microwave power generators in the radar program. Alvarez’s group included both his former graduate students and a number of talented individuals he had encountered during the war, most notably Wolfgang Panofsky, who subsequently led the effort to create the Stanford Linear Accelerator (linac). Alvarez’s machine made modest contributions to studies of nuclear scattering but was soon abandoned for higher-energy machines. The design, however, was incorporated as an injector of protons and heavier ions in many postwar synchrotrons.

After the first Soviet atomic bomb was detected in September 1949, Lawrence again mobilized Alvarez for nuclear weapons development. With Edward Teller, the two men successfully advocated the development of the “Super,” or hydrogen bomb, over the opposition of the General Advisory Committee (GAC) of the Atomic Energy Commission, chaired by their former University of California colleague, Robert Oppenheimer. Lawrence had proposed to build a heavy-water reactor to provide tritium for the Super, but when the GAC rejected the project, turned to the manufacture of fissile materials by electronu-clear means. The Oak Ridge and Argonne National Laboratories retained their reactor responsibilities.

At a formal Naval Air Station in Livermore, California, Alvarez’s linac was scaled up some four hundred times to produce deuterium ions that could be turned on various targets, depending on the material desired. Although the prototype was made to work with great difficulty, discovery of uranium on the Colorado plateau made such an expensive alternative unnecessary.

The crash program to develop the hydrogen bomb interfered with Alvarez’s scientific career, as had World War II. Although developments in liquid-hydrogen technology associated with the first thermonuclear tests bore fruit in his later development of the bubble chamber, he paid a price in terms of his career as a research scientist. He also lost the esteem of his fellow physicists when he sided against Oppenheimer in the advocacy of the Super. When Oppenheimer was called to account by political enemies in the Eisenhower administration in 1954, Alvarez testified, along with Edward Teller, in support of the interpretation of Oppenheimer’s obstruction to this development as unwise. He did not go so far as Teller in suggesting Oppenheimer’s disloyalty, but helped to give the hearing panel a reason to terminate Oppenheimer’s clearance.

Bubble Chambers and Big Science. Alvarez returned to Berkeley and began a new career in particle physics in 1954 just as the Bevatron, a 6.2-billion-electron-volt proton accelerator, was being completed by the Radiation Laboratory. He recognized that traditional nuclear detectors would not work well with the output of the new machine, which would be the highest-energy machine in existence. Learning of the invention of the bubble chamber by Donald Glaser of the University of Michigan, he undertook to build a series of such chambers at the Radiation Laboratory. As he had done with the MTA, Alvarez scaled up the chambers rapidly with generous subsidies from the Atomic Energy Commission, from 1.5 inches to 72 inches between 1955 and 1959. He recognized the need for automated analysis of the resulting photographs, which were produced at a rate of several million per year, and organized a group of physicist-programmers to provide it. He also encouraged the development of mechanized means of scanning the photographs for interesting events, leading to the development of a series of track-following devices such as the Franckenstein, invented by James Franck. These ancillary devices made the bubble-chamber system an effective and productive means of detecting many new particles and particle resonances. This work resulted in the award of the Nobel Prize in Physics to Alvarez in 1968.

The virtue of the liquid-hydrogen bubble chamber lay in the simplicity of the target—the hydrogen atom. Unlike earlier bubble chambers, which used hydrocarbon compounds, interactions with hydrogen atoms by particles from the Bevatron were simple to interpret. A significant event was more easily identified, permitting semiautomated and automated techniques to be employed. Alvarez’s group introduced techniques comparable to those of the assembly line in automotive manufacture, including division of labor, continuous processing, and quality control. The “industrialization” of particle detectors exemplified in the liquid-hydrogen bubble chamber similarly enhanced productivity.

Alvarez and his group pursued their particles in much the same way Lawrence had sought new radioisotopes in the 1930s. By focusing on one subatomic particle at a time and thoroughly charting its interactions, they were able to resolve important questions in particle physics as well as to suggest new ones. Unencumbered by theoretical constraints, they demolished existing theory and forced new interpretations on the particle physics community. The bubble chamber, like the cyclotron for accelerators, became the detector of choice in high-energy physics laboratories in the 1960s, and, like his mentor Lawrence, Alvarez was generous with help to would-be emulators of his system, supplying bubble-chamber film to those who did not have the means to produce it at their own laboratories.

Public Scientist. After Lawrence died at the age of fifty-seven in 1958, however, Alvarez chose not to follow Lawrence’s example in laboratory administration. Offered the directorship of the Lawrence Radiation Laboratory by University of California President Clark Kerr, Alvarez elected to remain head of his bubble-chamber group. McMillan, who succeeded Lawrence as director, did not succeed in winning Alvarez’s loyalty, and this led to Alvarez’s resignation as associate director and, eventually, his decision to pursue new activities.

Alvarez enjoyed the role of Cold War scientist and turned increasingly to service on panels of scientific advisors to the Atomic Energy Commission and the Department of Defense, as well as other government and private agencies interested in radar, aviation, and nuclear weapons. He was an advisor to the Central Intelligence Agency, National Security Agency, and Federal Aviation Administration, among others. Science policy was largely shaped by physicists of his generation. This branch of science in particular enjoyed substantial federal research funding and, as a part of the elite military-industrial complex, played a crucial role in directing that expenditure. Alvarez was able to acquire funding for his group from the National Aeronautics and Space Administration when he decided to resign from the administration of the Lawrence Radiation Laboratory, for example, to make a search for the magnetic monopoles that physical theory predicted, but which his team failed to find either in meteorites or in lunar rock samples, where long-term cosmic-ray bombardment should have made them.

Return to Cosmic Rays. Alvarez simultaneously searched cosmic rays for evidence of the antimatter that Hannes Alfven had predicted should enter the earth’s galaxy from galaxies made of it and separated from this galaxy by an electron plasma. He used a five-ton superconducting magnet borne aloft by balloons to detect them and, when that failed, undertook a survey with smaller superconducting magnets. As with the magneton, this search served to establish that these visitors were undetectable.

Alvarez also found an archaeological use for cosmic rays. The pyramid of Chephren at Giza had only one subterranean chamber, unlike the two constructed by his predecessors, and Alvarez believed that there might be other chambers that could be revealed by “x-raying” the pyramid with cosmic-ray muons, whose passage through the stone would be less attenuated by such voids in the pyramid’s structure. Despite the Arab-Israeli War of 1967, which forced his team of American and Egyptian physicists to postpone their work, the spark-chamber detectors he placed in the subterranean chamber made an extensive survey of incoming muons and found no hidden chambers. The method is still used in the early twenty-first century to investigate massive structures.

Nobel Prize. In 1968, Alvarez was awarded the Nobel Prize in Physics for his bubble-chamber work and the resulting discoveries. Although he had been disappointed when he did not receive the prize jointly with Donald Glaser in 1961 and trailed his other Radiation Laboratory colleagues Lawrence, McMillan, Seaborg, Segrè, and Owen Chamberlain to Stockholm, he made the most of his undivided funds by inviting the senior members of his group to join him there for the award ceremonies and took some condolence that while not the earliest, his was the longest prize citation for the award. Unlike many Nobel laureates, he resolved not to accept the social liabilities that usually come with the prize, and refused to sign petitions and attend other celebrations, including the Lawrence Radiation Laboratory party held in his honor by McMillan.

Alvarez did enjoy the liberation from his quotidian duties at the laboratory to investigate unusual phenomena. His attention was drawn to the ongoing controversy surrounding the assassination of John F. Kennedy when he was given access to the only visual recording of that incident, the Zapruder film made by an amateur photographer in Dallas at the time. Many critics of the Warren Commission, which conducted an investigation of the assassination and concluded that a lone gunman, Lee Harvey Oswald, perpetrated it, believed the film belied that conclusion. Alvarez systematically tackled the analysis of the film and found that it supported the commission’s conclusion, particularly with respect to Kennedy’s physical response to the fatal shot and with respect to the timing of the three shots. As an example of forensic science, his study was a tour de force that undermined alternative scenarios that had become a leitmotif of the 1970s.

His last experiment in forensic science dealt with the mass extinction of dinosaurs and other species. His son, Walter, who had become a geologist, detected a thin layer of clay laid down at approximately the same period as the dinosaurs’ disappearance, and brought a sample of it to Luis Alvarez’s attention. Intrigued by the association, Luis suggested that they measure the length of time that had been required to make the deposit. In order to determine the age of the clay, Luis thought first to use as tracers radioactive elements produced in the Earth’s atmosphere by cosmic rays (e.g., carbon-14). However, their lifetimes proved an order of magnitude too small, so Luis elected to search for elements that were more abundant in meteorite debris than in normal soil. Iridium was detected by Radiation Laboratory nuclear chemists using neutron activation analysis and proved three hundred times more abundant in the clay layer than in the surrounding limestone layers.

Subsequent investigation revealed that the layer also did not have elements associated with supernovae, thought by some to have caused the mass extinction, and through a process of elimination Alvarez concluded that a ten-kilometer meteor had struck the earth and created a dust cloud that orbited it long enough to cause the extinctions by cooling and interfering with plant growth.

Alvarez’s explanation of the Cretaceous-Tertiary mass extinction has won increasing acceptance among paleontologists, especially since a candidate impact site was discovered in the Yucatan peninsula of Mexico. Although there are competing theories that seek to account for the extinction in terms of terrestrial causes, the Alvarez hypothesis has not been refuted, and he believed it would be the scientific accomplishment for which he would be longest remembered.

Alvarez’s discoveries and inventions made him one of the most remarkable and versatile scientists of the twentieth century, and his technological accomplishments were both abundant and profitable, giving rise to a variety of spin-off firms from which he drew profit as well as pride. In addition to his many radar patents, he also held patents for electronuclear machines, x-ray detectors for explosives in airline baggage, optical systems, and range detectors for golf carts. For these accomplishments he was elected to the Inventors’ Hall of Fame, and won numerous awards, including the Collier Trophy of the National Aeronautical Association, the National Medal of Science, and the Pioneer Medal of the American Institute of Electrical and Electronic Engineers.

On 1 September 1988, a year after he completed his autobiography, Alvarez died of cancer in Berkeley, California. His work in high-energy physics had transformed experimental practice by importing collaborative research into the laboratory, as historian Peter Galison has shown, and contributed to the triumph of “big science” in the twentieth century.



With Arthur H. Compton. “A Positively Charged Component of Cosmic Rays.” Physical Review43 (1933): 835–836. An account of the discovery of the east-west effect in cosmic radiation.

“Capture of Orbital Electrons by Nuclei.” Physical Review54 (1938): 486–497.

With Robert Cornog. “Helium and Hydrogen of Mass 3.” Physical Review56 (1939): 613.

With Felix Bloch. “A Quantitative Determination of the Neutron Moment in Absolute Nuclear Magnetons.” Physical Review57 (1940): 111–122.

With Hugh Bradner, James V. Franck, Hayden Gordon, et al. “Berkeley Proton Linear Accelerator.” Review of Scientific Instruments 26 (1955): 111–133.

With Frank S. Crawford, Myron L. Good, and M. Lynn Stevenson. “Lifetime of K-Mesons.” Physical Review 101 (1956): 503–505.

With Hugh Bradner, Frank S. Crawford Jr., J. A. Crawford, et al. “Catalysis of Nuclear Reactions by μ-Mesons.” Physical Review 105 (1957): 1127–1128.

“High-Energy Physics with Hydrogen Bubble Chambers.” In Proceedings of the Second United Nations International Conference on Peaceful Uses of Atomic Energy, vol. 30, Fundamental Physics. Geneva: United Nations, 1958.

With Phillipe Eberhard, M. L. Good, William Graziano, et al. “Neutral Cascade Hyperon Event.” Physical Review Letters 2 (1959): 215–219.

With Margaret Alston, Phillipe Eberhard, M. L. Good, et al. “Resonance in the Λ-Π System.” Physical Review Letters 5 (1960): 520–524.

With Margaret Alston, William Graziano, M. L. Good, et al. “Resonance in the K-Π System.” Physical Review Letters 6 (1961): 300–302.

With D. O. Huwe, G. R. Kalbfleisch, Margaret Alston, et al. “The 1660 MeV Y*1 Hyperon.” Physical Review Letters 10 (1963): 184–188.

“A Physicist Examines the Kennedy Assassination Film.” American Journal of Physics44 (1976): 813.

With Walter Alvarez, Frank Asaro, and Helen V. Michel. “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction.” Science 208 (1980): 1095.

Alvarez: Adventures of a Physicist. New York: Basic Books, 1987.


Galison, Peter. Image and Logic: A Material Culture of Microphysics. Chicago: University of Chicago Press, 1997.

Garwin, Richard L. “Memorial Tribute for Luis W. Alvarez.” Memorial Tributes, National Academy of Engineering, vol. 5. Washington, DC: National Academy Press, 1992.

Trower, W. Peter, ed. Discovering Alvarez: Selected Works of Luis W. Alvarez with Commentary by His Students and Colleagues. Chicago: University of Chicago Press, 1987.

Heilbron, John, and Robert Seidel. Lawrence and His Laboratory, vol. 1, A History of the Lawrence Berkeley Laboratory. Berkeley: University of California Press, 1989.

Robert W. Seidel

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Alvarez, Luis Walter: 1911-1988: Nuclear Physicist, Inventor, Educator

Luis Walter Alvarez: 1911-1988: Nuclear physicist, inventor, educator

One of the most versatile scientists and inventors of the 20th century, Luis Walter Alvarez used his expertise to impact optics, flight, warfare, and the tracking and measurement of subatomic particles. During World War II, he joined the Manhattan Project to further the creation of the atomic bomb. Upon return to research and teaching, he created a bubble chamber for studying subatomic particles, a device that won him the 1968 Nobel Prize in physics. Always committed to problem-solving, Alvarez also investigated the construction of the Egyptian pyramid of Kefren and proposed a theory explaining the extinction of dinosaurs 65 million years ago from the collision of a meteorite or comet with Earth.

Early Laboratory Experience

As a child, Alvarez gained valuable experience wiring electrical circuits while working in the shop of his father, Dr. Walter Clement Alvarez, a medical researcher in physiology at the University of California at San Francisco. When the family moved to Rochester, Minnesota, Luis Alvarez attended Rochester High School and apprenticed under a machinist at the instrument workshop at the Mayo Clinic, where his father was employed. In Alvarez's junior year at the University of Chicago, he changed majors from organic chemistry to physics, the source of his interest in optics. While taking twelve physics courses in five quarters, he worked with technicians in the optical lab of Albert Michelson and, on his own, devoured Michelson's articles. Alvarez's first published paper explained how to measure light wavelength using a lamp, phonograph record, and yardstick. By studying Hans Geiger's writings, Alvarez built one of America's first Geiger counters, a device to measure radioactivity.

Although Alvarez later criticized his basic education in the sciences, he appreciated having Nobel Laureate Arthur Compton for a mentor and learned on his own to build with glass and metal. Richard L. Garwin, who published a tribute to Alvarez's career in a 1987 issue of Physics Today, quoted Alvarez's version of how he learned to work independently by reading primary source materials: "I had the enormous self-confidence to be expected of a Robinson Crusoe who had spent three years on a desert island. I had browsed the library so thoroughly that I knew where to find the books I needed to learn almost anything I wanted to know." His humble reflection omits the fact that, years later, he could recite data, journal issue, author, and page on which information appeared.

At a Glance . . .

Born Luis Walter Alvarez on June 13, 1911, in San Francisco, California; died August 31, 1988 in Berkeley, California; married Harriet S. Smyth (divorced); married Janet Landis; children: (with Smyth)Walter, (with Landis) Donald, Helen. Education: University of Chicago, B.S., physics, 1932, M.S.,1934, Ph.D., 1936.

Career: University of California, faculty member, 1936-78; MIT, 1940-43; radar research and development, MIT, radar research and development, 1944-45; University of California, Berkeley, professor of physics, 1945-78; Lawrence Radiation Laboratory, associate director, 1945-59; University of California, Berkeley, professor emeritus, 1978-88.

Memberships: American Physical Society, president, 1969; Institut D'Egypt, associate; National Academy of Scientists, National Academy of Engineering; American Physical Society, American Academy of Arts and Sciences; Phi Beta Kappa; Sigma Xi.

Awards: National Aeronautical Associations's Collier Air Trophy, 1946; Medal for Merit, 1948; the city of Philadelphia's John Scott Medal and Prize, 1953; California Scientist of the Year, 1960; Einstein medal, 1961; Pioneer Award, 1963; National Medal of Science, 1964; Michelson Award, 1965; Nobel Prize in Physics, 1968; National Inventors Hall of Fame, 1978; Dudley Wright Prize in Interdisciplinary Science, 1981; Rockwell Medal, 1986; Enrico Fermi Award, U. S. Energy Department, 1987; honorary doctorates from the University of Chicago, 1967, Carnegie Mellon University, 1968, Kenyon College, 1969, Notre Dame University, 1976, Ain Shams University, Cairo, 1979, and Pennsylvania College of Optometry, 1982.

At age 23 Alvarez mastered aviation with the same passion with which he tackled other new skills. After only three hours of dual instruction, he flew solo. His license was the beginning of a half century of flying. In 1936 he and his wife, Harriet S. Smyth Alvarez, settled in Berkeley, California and reared a son, Walter. For most of his life, Alvarez worked in the Radiation Laboratory, a university atmosphere that suited him. Before beginning any projects, he read all the library's holdings on the subject of nuclear physics and memorized the equipment layout of every lab drawer and cabinet shelf. One of his first contributions to the laboratory was the reclamation of a neglected cyclotron, a device that accelerates charged particles. Nurturing his curiosity were Monday evenings spent with Nobel Prize-winning physicist Ernest Orlando Lawrence at the journal club and a subsequent introduction to Hans Bethe's overviews of nuclear physics in Reviews of Modern Physics, which challenged Alvarez to disprove them.

Inventor and Researcher

Some of Alvarez's most significant contributions to physics were the process of K-electron capture, by which he discovered that nuclei gobble up their own electrons, and the development of the mercury vapor lamp, which produced a light wavelength that the U.S. Bureau of Standards adopted as its official measure of length. Among his breakthroughs was the discovery of the east-west effect of cosmic rays, which he and Arthur Compton studied while occupying the roof of Mexico City's Geneva Hotel with a Geiger telescope mounted on a wheelbarrow. In collaboration with Nobel Prize-winning physicist Felix Block of Stanford University, Alvarez produced slow-moving neutrons to determine their magnetic moment.

World War II placed Alvarez at an historic place and time and allowed him the opportunity to assist the war effort through research and invention. He introduced heavy-ion physics by identifying tritium, a radioactive form of hydrogen, and by deducing that helium-3 stabilized ordinary helium. In 1940 he developed radar systems for the U.S. military at the Massachusetts Institute of Technology radiation laboratory. He also developed a narrow radar beam to aid the landing of aircraft by a ground-based controller and produced Vixen, a system that diminished returning radar messages to convince German U-boat commanders that an attack plane was flying out of range. He created the Eagle high-altitude bombing system, a radar-guided means of sighting and dropping bombs on objects out of the pilot's range of vision. His microwave early-warning system solved the problem of sighting aircraft through fog, dust, or heavy cloud banks.

Two years before the end of World War II, as American scientists raced to outmaneuver the Germans in creating deadlier bombs, Alvarez joined the Manhattan Project, a team effort located at Los Alamos, New Mexico. His contribution was a detonator to set off the first plutonium bomb. During the initial atomic test at Alamogordo, New Mexico, on July 16, 1945, he flew with observers in a B-29 bomber. When the army dropped the "Fat Man" bomb on Hiroshima, Japan, on August 6, 1945, Alvarez observed from the B-29 that followed the bomber Enola Gay. The terrifying destruction of the unsuspecting city below alarmed Alvarez, but he maintained that the device was essential to end the war before Japan inflicted lasting harm on the United States. He also supported the creation of a hydrogen bomb to ensure national security.

A Professor Once More

After WWII, Alvarez returned to Berkeley to assume a full professorship and research high-energy nuclear physics. Applying the methods of Ernest Lawrence and Ernest Rutherford, he developed LINEAC, also called the Alvarez accelerator, which increased proton velocity. He tinkered with the mechanism until it became operational in 1947 and used it and the university's Bevatron to advance post-war physics. His advancement of nuclear physics distinguished Berkeley as a center of subatomic particle study. In the college laboratory, he constructed a synchrocyclotron, which boosted particulate speed to new levels.

After meeting with physicist Donald Glaser of the University of Michigan in 1953, Alvarez increased the capabilities of the first bubble chamber, a one-inch container of superheated ether in which observers could track the paths of subatomic particles. After replacing ether with liquid hydrogen, he invented equipment that recorded particle movements to within one billionth of a second. Within five years, he enlarged the bubble chamber to 72 inches and initiated its use in 1959, when he recorded a series of observations of baryons, mesons, and other minute particles in resonance states. As he worked on projects affecting national security, Alvarez received access to National Security Agency data, a trust that made him proud. His skillful problem-solving in the study of subatomic particles within cloud chambers earned him the 1968 Nobel Prize for physics, which he accepted in the company of his second wife, Janet Landis Alvarez, mother of their children, Donald and Helen. Sten von Friesen of the Swedish academy of Science credited Alvarez with opening paths to a whole field of discoveries in high-energy physics.

Alvarez applied highly theoretical research to unusual problems. He joined the Warren Commission in 1963 to establish that President John F. Kennedy was assassinated by a lone gunman rather than a team of shooters. In 1965 he aided paleontologists of an American and Egyptian expedition in a study of King Kefren's pyramid at Giza. By channeling subatomic particles called muons through the stone tomb, he deduced that there is no hidden burial chamber in the structure.

In 1980 Alvarez worked with his son, Walter, a professor of geology at the University of California Berkeley, to determine and explain the existence of an inch-deep sediment of iridium-laced clay on rocky hillsides in Italy.

The presence of the rare metal convinced the two scientists that an asteroid or comet deposited it after colliding with earth 65 million years ago. They theorized that the impact raised so thick a cloud of dust and smoke that it blocked out sunlight and lowered temperatures, causing plants to shrivel and herbivorous dinosaurs to die of starvation and extreme cold. They surmised that the event obliterated 70 percent of earth's species. Highly debated at first, the theory was eventually corroborated by scientists who located the Chiczulub crater in the Yucatan, Mexico. Good-humoredly, Alvarez tweaked paleontologists for missing the telltale layer and called them poor scientists more suited to stamp collecting.

A Lifetime of Useful Work

At his death from cancer in Berkeley on August 31, 1988, Alvarez left numerous discoveries and 22 patents, including a radio distance and direction indicator and the Tandem van de Graaff generator, a charge-altering electrostatic accelerator that was later produced commercially. He devised a color television system, a stabilizer for the binoculars and cameras marketed by Schwem Technologies, a variable-power lens for Polaroid and Humphrey Instruments, and President Dwight D. Eisenhower's personal indoor golf practice machine. He directed projects for Hewlett-Packard and served IBM's Science Advisory Committee. The Nobel-Prize winner's contributions to American science were profound, and his many awards reflect the appreciation of the scientific community in which he found his intellectual home.



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Albuquerque Journal, September 23, 2001, p. B3.

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http://www.nobel.se/physics/laureates/1968/alva rez-bio.html

Mary Ellen Snodgrass

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Snodgrass, Mary Ellen. "Alvarez, Luis Walter: 1911-1988: Nuclear Physicist, Inventor, Educator." Contemporary Hispanic Biography. 2003. Encyclopedia.com. 29 May. 2016 <http://www.encyclopedia.com>.

Snodgrass, Mary Ellen. "Alvarez, Luis Walter: 1911-1988: Nuclear Physicist, Inventor, Educator." Contemporary Hispanic Biography. 2003. Encyclopedia.com. (May 29, 2016). http://www.encyclopedia.com/doc/1G2-3433800011.html

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Alvarez, Luis (1911-1988)

Alvarez, Luis (1911-1988)

American physicist

Luis Alvarez proposed a controversial theory involving the possibility of a massive collision of a meteorite with the earth 65 million years ago, an event that Alvarez believed may account for the disappearance of the dinosaurs. After a varied and illustrious career as a Nobel Prize-winning physicist, Alvarez shared his last major scientific achievement with his son Walter, who was then a professor of geology at The University of California at Berkeley. In 1980, the Alvarezes accidentally discovered a band of sedimentary rock in Italy that contained an unusually high level of the rare metal iridium. Dating techniques set the age of the layer at about 65 million years. The Alvarezes hypothesized that the iridium came from an asteroid that struck the earth, thereby sending huge volumes of smoke and dust (including the iridium) into the earth's atmosphere. They suggested that the cloud produced by the asteroid's impact covered the planet for an extended period of time, blocked out sunlight, and caused the widespread death of plant life on Earth's surface. The loss of plant life in turn, they theorized, brought about the extinction of dinosaurs, who fed on the plants. While the theory has found favor among many scientists and has been enhanced by additional findings, it is still the subject of scientific debate.

Luis Walter Alvarez was born in San Francisco, California. His father, Dr. Walter Clement Alvarez, was a medical researcher at the University of California at San Francisco and also maintained a private practice. Luis' mother was the former Harriet Skidmore Smythe. Alvarez's parents met while studying at the University of California at Berkeley.

Alvarez attended grammar school in San Francisco and enrolled in the city's Polytechnic High School, where he avidly studied science. When his father accepted a position at the prestigious Mayo Clinic, the family moved to Rochester, Minnesota. Alvarez reported in his autobiography Alvarez: Adventures of a Physicist, that his science classes at Rochester High School were "adequately taught [but] not very interesting." Dr. Alvarez noticed his son's growing interest in physics and hired one of the Mayo Clinic's machinists to give Luis private lessons on weekends. Alvarez enrolled at the University of Chicago in 1928 and planned to major in chemistry . He was especially interested in organic chemistry, but soon came to despise the mandatory chemistry laboratories. Alvarez "discovered" physics in his junior year and enrolled in a laboratory course, "Advanced Experimental Physics: Light" about which he later wrote in his autobiography: "It was love at first sight." He changed his major to physics and received his B.S. in 1932. Alvarez stayed at Chicago for his graduate work and his assigned advisor was Nobel Laureate Arthur Compton, whom Alvarez considered "the ideal graduate advisor for me" because he visited Alvarez's laboratory only once during his graduate career and "usually had no idea how I was spending my time."

Alvarez earned his bachelor's, master's, and doctoral degrees at the University of Chicago before joining the faculty at the University of California at Berkeley, where he remained until retiring in 1978. His doctoral dissertation concerned the diffraction of light, a topic considered relatively trivial, but his other graduate work proved to be more useful. In one series of experiments, for example, he and some colleagues discovered the "east-west effect" of cosmic rays, which explained that the number of cosmic rays reaching the earth's atmosphere differed depending on the direction from which they came. The east-west effect was evidence that cosmic rays consist of some kind of positively charged particles. A few days after passing his oral examinations for the Ph.D. degree, Alvarez married Geraldine Smithwick, a senior at the University of Chicago, with whom he later had two children. Less than a month after their wedding, the Alvarezes moved to Berkeley, California, where Luis became a research scientist with Nobel Prize-winning physicist Ernest Orlando Lawrence, and initiated an association with the University of California that was to continue for forty-two years.

Alvarez soon earned the title "prize wild idea man" from his colleagues because of his involvement in such a wide variety of research activities. Within his first year at Berkeley, he discovered the process of K-electron capture, in which some atomic nuclei decay by absorbing one of the electrons in its first orbital (part of the nuclear shell). Alvarez and a student, Jake Wiens, also developed a mercury vapor lamp consisting of the artificial isotope mercury198. The U.S. Bureau of Standards adopted the wavelength of the light emitted by the lamp as an official standard of length. In his research with Nobel Prize-winning physicist Felix Bloch, Alvarez developed a method for producing a beam of slow moving neutrons, a method that was used to determine the magnetic moment of neutrons (the extent to which they affect a magnetic field ). Just after the outbreak of World War II in Europe , Alvarez discovered tritium, a radioactive isotope (a variant atom containing a different number of protons) of hydrogen.

World War II interrupted Alvarez's work at Berkeley. In 1940, he began research for the military at Massachusetts Institute of Technology's (MIT's) radiation laboratory on radar (radio detecting and ranging) systems. Over the next three years, he was involved in the development of three new types of radar systems. The first made use of a very narrow radar beam to allow a ground-based controller to direct the "blind" landing of an airplane. The second system, code-named "Eagle," was a method for locating and bombing objects on the ground when a pilot could not see them. The third invention became known as the microwave early-warning system, a mechanism for collecting images of aircraft movement in overcast skies.

In 1943, Alvarez left MIT to join the Manhattan Project research team working in Los Alamos, New Mexico. His primary accomplishment with the team was developing the detonating device used for the first plutonium bomb. Alvarez flew in the B29 bomber that observed the first test of an atomic device at Alamogordo, south of Los Alamos. Three weeks later, Alvarez was aboard another B29 following the bomber "Enola Gay" as it dropped the first atomic bomb on Hiroshima, Japan. Like most scientists associated with the Manhattan Project, Alvarez was stunned and horrified by the destructiveness of the weapon he had helped to create. Nonetheless, he never expressed any doubts or hesitation about the decision to use the bombs, since they brought a swift end to the war. Alvarez felt strongly that the United States should continue its nuclear weapons development after the war and develop a fusion (hydrogen) bomb as soon as possible.

After the war, Alvarez returned to Berkeley where he had been promoted to full professor. Determining that the future of nuclear physics lay in high-energy research, he focused his research on powerful particle acceleratorsdevices that accelerate electrons and protons to high velocity. His first project was to design and construct a linear accelerator for use with protons. Although his machine was similar in some ways to the electron accelerators that had been available for many years, the proton machine posed a number of new problems. By 1947, however, Alvarez had solved those problems and his forty-foot-long proton accelerator began operation.

Over the next decade, the science of particle physics (the study of atomic components) developed rapidly at Berkeley. An important factor in that progress was the construction of the 184-inch synchrocyclotron at the university's radiation laboratory. The synchrocyclotron was a modified circular particle accelerator capable of achieving much greater velocities than any other type of accelerator. The science of particle physics involves two fundamental problems: creation of particles to be studied in some type of accelerator and detection and identification of those particles. After 1950, Alvarez's interests shifted from the first to the second of these problems, particle detection, because of a chance meeting in 1953 with University of Michigan physicist Donald Glaser. Glaser had recently invented the bubble chamber, a device that detects particles as they pass through a container of superheated fluid. As the particles move through the liquid, they form ions that act as nuclei on which the superheated material can begin to boil, thereby forming a track of tiny bubbles that shows the path taken by the particles. In talking with Glaser, Alvarez realized that the bubble chamber could be refined and improved to track the dozens of new particles then being produced in Berkeley's giant synchrocyclotron. Among these particles were some with very short lifetimes known as resonance states.

Improving Glaser's original bubble chamber involved a number of changes. First, Alvarez decided that liquid hydrogen would be a more sensitive material to use than the diethyl ether employed by Glaser. In addition, he realized that sophisticated equipment would be needed to respond to and record the resonance states that often lasted no more than a billionth of a second. The equipment he developed included relay systems that transmitted messages at high speeds and computer programs that could sort out significant from insignificant events and then analyze the former. Finally, Alvarez aimed at constructing larger and larger bubble chambers to record a greater number of events. Over a period of about five years, Alvarez's chambers grew from a simple one-inch glass tube to his most ambitious instrument, a 72-in (183 cm) chamber that was first put into use in 1959. With these devices, Alvarez eventually discovered dozens of new elementary particles, including the unusual resonance states.

The significance of Alvarez's work with bubble chambers was recognized in 1968 when he was awarded the Nobel Prize for physics. At the awards ceremony in Stockholm, the Swedish Academy of Science's Sten von Friesen stated that, because of his work with the bubble chamber, "entirely new possibilities for research into high-energy physics present themselves.Practically all the discoveries that have beenmade in this important field [of particle physics] have been possible only through the use of methods developed by Professor Alvarez." Alvarez attended the Nobel ceremonies with his second wife, Janet Landis, whom he married in 1958. The couple had two children.

Advancing years failed to reduce Alvarez's curiosity on a wide range of topics. In 1965 he was in charge of a joint Egyptian-American expedition whose goal was to search for hidden chambers in the pyramid of King Kefren at Giza. The team aimed high-energy muons (subatomic particles produced by cosmic rays) at the pyramid to look for regions of low density, which would indicate possible chambers. However, none were found. Alvarez's hobbies included flying, golf, music, and inventing. He made his last flight in his Cessna 310 in 1984, almost exactly 50 years after he first learned to fly. In 1963, he assisted the Warren Commission in the investigation of President John F. Kennedy's assassination. Among his inventions were a system for color television and an electronic indoor golf-training device developed for President Eisenhower. In all, he held 22 patents for his inventions. Alvarez died of cancer in Berkeley, at the age of 77.

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Luis W. Alvarez

Luis W. Alvarez

The importance and variety of the discoveries and contributions of Luis W. Alvarez (1911-1988) are perhaps unmatched by any other 20th-century physicist. He received many awards for his work over the years, including the 1968 Nobel Prize in Physics for his work on a large liquid hydrogen bubble chamber.

Alvarez will probably be best remembered by the public for ingenious experiments that applied physics to other sciences. He x-rayed Chephren's pyramid in Egypt using cosmic radiation, only to find that there were no undiscovered chambers inside. His application of elementary physics to the evidence on the John F. Kennedy assassination verified the Warren Commission finding that only a single assassin was involved. But perhaps his most dramatic discovery was made after his "retirement" by jumping into a totally new field, paleontology and geology. With collaborators that included his son, Walter, he analyzed a 65 million year old clay layer and showed that the great ecological catastrophe that killed the dinosaurs was caused by the impact of an asteroid or comet.

Alvarez was born June 13, 1911, in San Francisco. He began his career at the University of Chicago. His first published paper (as an undergraduate) described a measurement of the wavelength of light using a phonograph record, a parlor lamp, and a yard stick. While reading the original physics literature, he found a paper by Hans Geiger that described a new type of detector for charged particles. He proceeded to construct one of the first Geiger counters in America. Alvarez was the first Chicago undergraduate to present results of his research at the weekly departmental colloquium, sharing the time with a professor who reported on James Chadwick's discovery of the neutron. After hearing the talk, Arthur Compton invited Alvarez to collaborate with him on a study to determine the electric charge of the primary cosmic radiation.

Alvarez's first summer as a graduate student was spent on the roof of the Geneva Hotel in Mexico City, his Geiger telescope resting in a wheelbarrow that allowed him to periodically reverse the east-west orientation of his apparatus. He and Compton determined that the cosmic rays were mostly positively charged, and therefore presumably protons. After receiving his Ph.D. in 1936 Alvarez began work with Ernest O. Lawrence at the University of California, in part through family connections. Alvarez's father, a physician on the staff of the Mayo Clinic, had helped Lawrence get money for one of his cyclotrons, and his sister was Lawrence's part-time secretary. Arriving at the Old Radiation Laboratory, Alvarez made the first of his dramatic career changes as he prepared himself to become a practicing nuclear physicist. First, he became thoroughly familiar with all instruments in the laboratory, their use, and the physics that was being done with them. He did this by helping everyone with their experiments while becoming a skilled machine operator and repairman.

Emerging from the laboratory at each day's end, Alvarez would pick up a couple of volumes of physics journals from the university library; he eventually read every published nuclear physics article held there. Years later he would astonish his colleagues by reproducing a curve or a little known fact gleaned in these early efforts. He could usually cite the authors, journal, year, and often the location of the volume in the library and whether the item was on a right-or a left-hand page. By 1937 Hans Bethe had published his three-part compendium of all that was known about nuclear physics. Alvarez chose first to make a measurement that Bethe said couldn't be done and then to disprove one of Bethe's assertions. In just four years Alvarez discovered the radioactivity of tritium and the stability of helium-3, the magnetic moment of the neutron, and that nuclei cannibalize their own atomic electrons. He also demonstrated the spin dependence of the nuclear force, established a new standard of length using mercury-198, and made the first experimental demonstrations in a field now called heavy-ion physics.

World War II ended Alvarez's nuclear physics career. He soon found himself in Boston, figuring how to apply high-frequency radio waves to achieve military goals. Using optics ideas learned in his thesis work, Luie invented the linear phased array, which formed the basis of EAGLE, the first radar bombing system. He also invented VIXEN, a system to outfox German submarines by diminishing an airborne acquisition radar's power as a surfaced sub was approached, so that the listening skipper would believe the attack plane was going away. Alvarez solved the problem of landing planes in bad weather by inventing the radar-based Ground Control Approach (GCA), for which he won the 1946 Collier Air Trophy.

Upon his return to the Berkeley laboratory after the war, Alvarez made another career change, to that of a particle accelerator physicist. He realized the importance of team research and looked to the methods of Lawrence and Ernest Rutherford. Like them, he displayed an ability to select good people to work with him.

His first postwar machine was the proton linear accelerator, which has become the standard injector for many subsequent higher energy circular machines and is still referred to as an "Alvarez accelerator." While preparing for his nuclear physics class one morning, he invented the Tandem van de Graaff, which was commercialized by High Voltage Engineering. Alvarez was a superb teacher. His course in physical optics was thorough. The students were introduced to the full spectrum of electromagnetic radiation from gamma rays to radio waves with spellbinding tales of how radar was used during the Battle of Britain.

In the mid 1950s Donald Glaser invented a new detector called a bubble chamber. Alvarez immediately saw the potential this had for the study of the newly available high-energy particles, if it could be made to work with liquified hydrogen. He established a group to develop the liquid-hydrogen bubble chamber from the first small steady-state chambers to large pulsed chambers. Characteristically, he grew impatient with the small chambers and proposed a large one 72 inches in length. This was nearly eight times the size of the one then in action at Berkeley, and some people thought this would be too big a step. Alvarez was confident that the chamber could be made to operate and he convinced the money sources to help. The 72-inch chamber aided in the identification of many new particles. It was for this work that he received the Nobel Prize in Physics in 1968.

In 1977 he was presented a piece of rock that had been cut from a hillside in Italy by his geologist son, Walter. The rock had a thin clay layer in it. He was shown how the microscopic fossils ("forams") in the rock became extinct right at the clay layer. These tiny forams had been destroyed at the clay layer. These tiny forams had been destroyed at the same time the dinosaurs had disappeared. Alvarez later described his experience in examining this rock as one of the most exciting moments in his life. The scientific consequences, which include the nuclear winter theory, are still being uncovered by geologists, paleontologists, physicists, chemists, and astronomers.

Alvarez was always solving practical problems that influenced his life. By his early fifties he needed bifocal lenses to correct his eyesight, and this convinced him that there must be a better way to solve this problem. The result was his invention of the variable focus lens and the formation of Humphrey Instruments.

While visiting Kenya, he was frustrated by how the image of the distant animals jumped around in the viewing port of his hand-held camera. He just couldn't hold the camera firmly enough to steady the image. He then invented a series of stabilized optical devices; and eventually he formed Schwem Technologies to develop and market them.

In addition to the 1946 Collier Air Trophy and the 1968 Nobel Prize in Physics, Alvarez also received the Einstein Medal in 1961, the 1964 National Medal of Science, a 1978 membership in the Inventors' Hall of Fame, and the 1981 Wright Prize.

Further Reading

Alvarez produced an extensive autobiography. A single volume version, Alvarez: Adventures of a Physicist was published in 1987, a paperback edition in 1989. He was honored by his colleagues with Discovering Alvarez; Selected Works of Luis W. Alvarez with Commentary by His Students and Colleagues, edited by W. Peter Trower (1987). □

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Alvarez, Luis Walter

Luis Walter Alvarez, 1911–88, American physicist, b. San Francisco, grad. Univ. of Chicago, 1932, Ph.D. 1936. He was awarded the 1968 Nobel Prize in Physics for his discovery of a large number of residence states (subatomic particles that have very short lifetimes and that occur only in high-energy nuclear collisions), which was made possible through his development of the liquid-hydrogen bubble chamber (see particle detector). He also helped develop the ground-control approach system for aircraft in the 1940s and played an important part in the Manhattan Project, where he suggested the technique for detonating the implosion type of atomic bomb. A member of the National Inventor's Hall of Fame, Alvarez held the patents for more than 30 inventions, including three types of radar systems. His autobiography, Alvarez: Adventures of a Physicist, was published in 1987. He; his son, the geologist Walter Alvarez, 1940–, b. Berkeley, Calif.; and others proposed that unusually high levels of iridium at the boundary between Cretaceous and Tertiary rocks indicated a major meteor impact with the earth about 65 million years ago and that this might be the cause of the mass extinction of the dinosaurs.

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Alvarez, Luis Walter

Alvarez, Luis Walter (1911–88) US physicist who received the 1968 Nobel Prize in physics for developing the liquid-hydrogen bubble chamber. Alvarez used it to identify many ‘resonances’ (very short-lived particles). He also helped construct the first proton linear accelerator. Alvarez worked on the Manhattan Project to develop the atom bomb, and invented a radar guidance system for aircraft.

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