Luis Walter Alvarez - Biography - Later Life and Career

Later Life and Career

Returning to the University of California as a full professor, Alvarez had many ideas about how to use his wartime radar knowledge to improve particle accelerators. Though some of these were to bear fruit, the "big idea" of this time would come from Edwin McMillan with his concept of phase stability which led to the synchrocyclotron. Refining and extending this concept, the Lawrence team would build the world's then-largest proton accelerator, the Bevatron, which began operating in 1954. Though the Bevatron could produce copious amounts of interesting particles, particularly in secondary collisions, there were very few techniques up to the task of detecting these complex interactions.

Seizing upon a new development to visualize particle tracks, created by Donald Glaser and known as a bubble chamber, Alvarez immediately realized the potential of the device if only it could be made to function with liquid hydrogen. Hydrogen nuclei, comprising only protons, made the simplest and most desirable target for interactions with the particles produced by the Bevatron. He immediately began an intensive development program to build a series of small chambers, and championed the device to Ernest Lawrence.

The Glaser device was a small glass cylinder (1 cm × 2 cm) filled with ether. By suddenly reducing the pressure the liquid could be placed into a temporary superheated state which would only boil along the disturbed track of a particle passing through. Glaser was able to maintain the superheated state for a few seconds before spontaneous boiling took place. The Alvarez team quickly built chambers of 1.5 in, 2.5 in, 4 in, 10 in, and 15 in using liquid hydrogen and constructed of metal with glass windows so that the tracks could be photographed. Another breakthrough was to cycle the chamber quickly in synchronization with the accelerator beam, take the picture, and then recompress the chamber in time for the next beam cycle.

Ultimately, this program would build a liquid hydrogen bubble chamber almost 7 feet (2 meters) long, employ dozens of physicists and graduate students together with hundreds of engineers and technicians, take millions of photographs of particle interactions, develop complex computer systems to measure and analyze these interactions, and discover entire families of new particles and resonance states. All of this work would result in the Nobel Prize in Physics for Alvarez in 1968

For his decisive contributions to elementary particle physics, in particular the discovery of a large number of resonant states, made possible through his development of the technique of using hydrogen bubble chambers and data analysis.

In 1964 Alvarez proposed what became known as the High Altitude Particle Physics Experiment (HAPPE), originally conceived as a large superconducting magnet carried to high altitude by a balloon in order to study extremely high-energy particle interactions. In time the focus of the experiment changed more toward the study of cosmology and the role of both particles and radiation in the early universe. This work was a large effort, carrying detectors aloft with high-altitude balloon flights and high-flying U2 aircraft, and was an early precursor of the COBE satellite-born experiments on the cosmic background radiation (which resulted in the award of the 2006 Nobel Prize, shared by George Smoot and John Mather.)

Alvarez proposed in 1965 to "X-Ray" the Egyptian pyramids to search for unknown chambers. Using naturally occurring cosmic rays, his ingenious scheme was to place spark chambers, standard equipment in the high-energy particle physics of this time, beneath the second pyramid of Chephren in a known chamber. By measuring the counting rate of the cosmic rays in different directions the detector would reveal the existence of any void in the overlaying rock structure.

Alvarez assembled an international team of physicists and archeologists from both the United States and Egypt, the recording equipment was constructed and the experiment carried out, though it was interrupted by the 1967 Six-Day War. Restarted after the war, the effort continued, recording and analyzing the penetrating cosmic rays until 1969 when Alvarez reported to the American Physical Society that no chambers had been found in the 19% of the pyramid surveyed.

In November 1966 Life Magazine published a series of photographs from the film that Abraham Zapruder took of the Kennedy assassination. Alvarez, an expert in optics and photoanalysis, became intrigued by the pictures and began to delve deeply into what could be learned from the film. The result of this was that Alvarez proved conclusively both in theory and experiment that the backward snap of the President’s head was completely consistent with his being shot from behind, which would have been the case if Lee Harvey Oswald were the assassin. He also investigated the timing of the gun shots and the shockwave which disturbed the camera, the speed of the camera, and pointed out a number of things which the FBI photoanalysts either overlooked or got wrong. He produced a paper intended as a tutorial, with informal advice for the physicist intent on arriving at the truth.