April 13: Bruno Benedetto Rossi

Bruno Benedetto Rossi

April 13, 1905 – November 21, 1993

Bruno Rossi was a leading Italian-American experimental physicist. He made major contributions to cosmic ray and particle physics from 1930 through the 1950s, and pioneered X-ray astronomy and space plasma physics in the 1960s.

Rossi was born in Venice, Italy. After receiving the doctorate degree from the University of Bologna, he began his career in 1928 as assistant at the Physics Institute of the University of Florence where he made his first discoveries regarding the nature of cosmic rays. In 1932 he was called to the University of Padua as professor of experimental physics. There, in addition to teaching and research, Rossi planned the new Physics Institute of the University and oversaw its construction. In the fall of 1938 he was expelled from his position as a result of the racial decrees of the fascist state. Rossi was Jewish and so was his wife, Nora Lombroso (granddaughter of anthropologist, Cesare Lombroso), so they had to leave Italy and traveled to America with brief stays in Copenhagen, Denmark and Manchester, England.

They arrived at the University of Chicago in June 1939 where he was given a temporary position as research associate. Rossi immediately began a series of experiments that yielded the first proof of the decay of a fundamental particle, the mesotron, now called muon, and a precise measurement of its mean life at rest. The latter was achieved at Cornell University where he was appointed associate professor in 1942. During the war Rossi worked first as consultant on radar development at the Radiation Laboratory of the Massachusetts Institute of Technology, and then at Los Alamos as co-director of the Detector Group responsible for development of instrumentation for experiments that supported the development of the atomic bombs.

In the fall of 1946 Rossi was appointed professor of physics at MIT where he established the Cosmic Ray Group to investigate the nature and origins of cosmic rays and the properties of the sub-nuclear particles produced in the interaction of cosmic rays with matter. In the late 1950s, when particle accelerator experiments had come to dominate experimental particle physics, Rossi turned his attention to exploratory research made possible by the new availability of space vehicles. At MIT he initiated rocket experiments that pioneered the direct measurements of the interplanetary plasma. As a consultant to American Science and Engineering, Inc. he initiated the rocket experiments that discovered the first extra-solar source of X-rays, Scorpius X-1. Rossi was made Institute Professor at MIT in 1965.

Among his contributions to the electronic techniques of experimental physics are the inventions of the coincidence circuit (Florence 1930), the time-to-amplitude converter (Cornell 1942) and the fast ionization chamber (Los Alamos, with H. Staub 1943).

Rossi retired from MIT in 1970. From 1974 to 1980 he taught at the University of Palermo. In 1990 his autobiography, titled Moments in the Life of a Scientist, was published by Cambridge University Press.