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Dr. Rudd's research in atomic collision physics has been characterized by originality and thoroughness. He has written review articles and chapters in the Encyclopedia of Physics - and elsewhere, and is a co-author on a book on atomic collisions. He has published more than 75 refereed research papers, many of which were of seminal importance. He was the first to study systematically the dependence of the probability for electron emission in ion-atom collisions on the incident ion's energy, and on the ejected electron's energy and angle of emission. In 1964 he made the first experimental observation of doubly excited atomic states produced by heavy particle impact on rare gas target ions with sufficient resolution to identify the states. In 1968 with Ted Jorgensen he made the first experimental observation of "Doppler shifts" of ejected electron spectra. In 1970 came his most famous "first", the observation that a significant component of the ejected electrons travel with a velocity equal to that of the incident ion (a mechanism of ionization called "electron capture to the continuum"). In a collaboration with Joe Macek, the electron promotion model was used to describe the ejection of high energy electrons in low energy collisions.
Rudd's pioneering work continues. He has begun the first experimental measurements of proton impact on atomic hydrogen. This process is fundamental because it involves only 3 particles, and hence has been well studied theoretically. It is fundamental in astrophysics since protons, electrons and hydrogen atoms are among the primary constituents of stars. His work is fundamental in other areas as well. Electrons ejected in atomic collisions in matter produce additional ionizations, and break molecular bonds. These processes produce radiation damage. Rudd's data has led to further investigations of biological effects of heavy ions in human tissue, of the effects of incident cosmic rays on computers in satellites, and to a host of other phenomena. It has been said by Eugen Merzbacher, former president of the American Physical Society, that Rudd's name among the authors of a research paper inspires general confidence in the results and vouches for their reliabilty. His painstaking data compilations have been of immense value to atomic and radiation effects physicists.