In memoriam: Ugo Fano (1912-2001).

With the passing of Ugo Fano on 13 February 2001, the Radiation Research Society lost an influential founding member. A broader community dearly misses a great theoretical physicist. Ugo Fano was born a son of Rosa Cassin and Gino Fano (1871-1952), professor of mathematics at Turin, Italy, specializing in differential geometry. Having studied mathematics first at the University of Turin, the younger Fano turned to physics under the influence of his cousin, Giulio Racah (1909-1965), a physicist known for the powerful theory of angular momentum. Then Fano was fortunate to receive postdoctoral training from two giants in modern physics: Enrico Fermi at Rome in 1934-1936 and Werner Heisenberg at Leipzig in 1936-1937. Fano's American career began with pioneering work in 1940-1944 in what was later to be called radiation biology with M. Demerec and others at the Department of Genetics of the Carnegie Institution at Cold Spring Harbor. It is noteworthy that, after a seminar in Rome by P. Jordan on the effects of X rays on genetic material, Fermi had suggested to Fano that the biological action of radiation would be an important and suitable topic for study. Fano's papers in this period concerned chromosomal rearrangements, mutations, lethal effects,more » and genetic effects of X rays and neutrons on Drosophila melanogaster, as well as theoretical analysis of genetic data. His work also included the discovery of bacteriophage-resistant mutants in Escherichia coli, following up earlier studies by Salvador E. Luria. After a wartime effort at the U.S. Army Ballistic Research Laboratory in 1944-1945, Fano joined the staff of the National Bureau of Standards in 1946. Fano's two decades at NBS saw prolific and outstanding contributions to two major areas of research: radiation physics and the basic physics of atoms, molecules and condensed matter. Many of Fano's contributions to radiation physics are seminal to later developments. In 1946, he put forth the first general theory of the yield of ionization in a gas. In 1947, he pointed out the statistical fluctuations of ionization and characterized them by what is now known as the Fano factor. In 1951-1959, he led L. V. Spencer, M. J. Berger and others in developing methods for treating the transport of photons and charged particles in matter. The invention in 1953-1954 of the degradation spectrum for characterizing electrons and other charged particles in matter was especially influential. In 1954, Fano also demonstrated the cavity principle of radiation equilibrium under general conditions. In later years at Chicago, he maintained a keen interest in radiation physics and studied topics such as the behavior of slow electrons in condensed matter, which are produced abundantly by any ionizing radiation. Fano's work after the mid-1950s focused increasingly on basic and microscopic aspects of radiation interactions with matter, including condensed-phase effects on radiation absorption (studied in 1956-1960) and stopping powers of materials (comprehensively reviewed in 1963). He continued for many years to campaign for the use of synchrotron radiation, for which numerous facilities have now been developed worldwide. The numerous, wide-ranging influences of Fano in basic physics and chemistry grew mostly from his years since 1966 at the University of Chicago. Not only did he train approximately 30 Ph.D. students and many postdoctoral fellows, but he communicated regularly with scientists around the world in meetings or by telephone calls, letters and electronic mail, liberally sharing his ideas and incisive insights into scientific matters. This style of 'doing physics' (in Fano's frequently used words) stems from Fermi, who strove to see the essence of knowledge in experimental facts and to tell it to others in simple and unpretentious words. We shall continue to learn much from his five monographs and over 250 papers.« less