Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session C5: Invited Session: The Scientific Legacy of Bruno Rossi |
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Sponsoring Units: FHP Chair: Daniel Kleppner, Massachusetts Institute of Technology Room: International Ballroom South |
Saturday, March 31, 2012 1:30PM - 2:06PM |
C5.00001: Rossi and high-energy astronomy Invited Speaker: George W. Clark The contributions of Bruno Rossi to high-energy astronomy began in Italy in the 1930s with investigations concerning the nature of cosmic rays in theory and in hands-on experiments at the universities of Florence and Padua. Recent discoveries had cast doubt on Robert Millikan's idea that the primary cosmic rays are gamma rays created in the production of the elements by fusion of hydrogen atoms in interstellar space. Rossi entered the field with a prediction published in 1930 of a difference between the intensity of cosmic rays from the east and the west that would occur if the primary cosmic rays were charged particles of one sign. In the same year he invented the first practical electronic coincidence circuit, which he used in a series of fundamental particle experiments and in an unsuccessful attempt to detect an east-west effect at Florence. Expecting by theory that the effect would be greater at high altitude near the equator, he took his experiment to Eritrea in 1934 where his measurements demonstrated that the primary cosmic rays are predominantly positive particles. In the report of his expedition he also described his discovery of extensive cosmic-ray air showers. After WWII and his work at Los Alamos, Rossi resumed his cosmic-ray research, now at MIT, in a new style best described in his own words: ``Now I had the responsibility of an entire group, and what mattered was no longer my own work, but the work of the group.'' He suggested the new methods of ``density sampling'' and ``fast timing'' for air shower studies, and promoted their application in numerous experiments on the nature and origins of the highest energy cosmic rays. In 1959 he initiated and participated as a consultant in the work of Riccardo Giacconi that led to the discovery of the first x-ray star, Sco X-1, and the development of the first imaging x-ray telescopes. At MIT, members of the Rossi Cosmic Ray Group took the early steps in gamma-ray astronomy, first with balloon experiments that set lower and lower limits on the intensity of primary gamma rays, and then with the satellite experiments led by William Kraushaar that discovered the galactic and extra-galactic components of cosmic gamma rays. After Sco X-1, Rossi focused his efforts on exploring the solar wind and the interplanetary plasma while leaving his younger colleagues to pursue the new field of extra-solar x-ray astronomy with balloon, rocket, and satellite experiments. [Preview Abstract] |
Saturday, March 31, 2012 2:06PM - 2:42PM |
C5.00002: Rossi and Space Physics Invited Speaker: Edward Stone The beginning of the Space Age opened a new realm of exploration and Bruno Rossi immediately focused on devising an instrument for studying the interplanetary environment. The modulated Faraday cup that he and his colleagues developed was launched on Explorer X on March 21, 1961. Although the lifetime of the battery-powered spacecraft was only 60 hours, that was long enough for the MIT plasma probe to reveal a hot, supersonic solar wind flowing along the flank of the Earth's magnetosphere. The legacy of that first short flight now extends outward on a 34-year journey to 98 AU where the plasma probe on Voyager 2 measures the deflection of the subsonic wind as it approaches the outer frontier of the heliosphere and contact with the interstellar plasma outside. Over the coming decade that legacy will extend inward to within 0.05 AU of the Sun as the plasma probe on Solar Probe Plus explores the region near the inner frontier and the source of the supersonic solar wind. The exploration of the solar wind from near its beginning outward to its end will be a lasting tribute to Bruno Rossi's contributions to Space Physics. [Preview Abstract] |
Saturday, March 31, 2012 2:42PM - 3:18PM |
C5.00003: Bruno Rossi: Cosmic Ray Research 1929 - 1953 Invited Speaker: Jim Cronin Bruno Rossi, a fresh PhD from the University of Bologna, arrived in Florence in 1928. He was appointed assistant to Antonio Garbasso, professor of experimental physics. Garbosso at that time was Mayor of Florence. His days of physics were over which gave the young Rossi a freedom to follow any line of research. After some agonizing he came upon research in cosmic rays following the discovery that a large part of the cosmic rays were charged particles. Thus began a long period of creative research. Rossi had all the talents needed, a powerful intellect and the natural ability to construct apparatus that gave clear results for his experiments. I will give some examples of his many discoveries concerning the nature of cosmic rays. [Preview Abstract] |
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