Sergei Pavlovich Kruglov

Sergei Pavlovich Kruglov, professor and chief researcher at PNPI, Gatchina, Russia died peacefully in his sleep on 20 January 2014 following a brief hospitalization. Sergey was Honored Scientist of the Russian Federation and a leading figure in meson physics and electromagnetic interaction; among his most notable contributions is the Muon Spin Rotation (µSR) study.

Sergey was born in Vologda on 5 April 1929. Admitted to the St. Petersburg State Polytechnic University (former Leningrad Polytechnic Institute), Sergey received his MA degree in nuclear physics in 1953. He then went to Petersburg Nuclear Physics Institute (former Leningrad Nuclear Physics Institute and Ioffe Physical-Technical Institute), and in 1961 received his Ph.D. on comparison of ionization and calorimetric measurements of the energy flux of gamma radiation from electron accelerators, with Anton Komar as his adviser. Sergey summarized his study in a book Measurement of the total energy of the beams from the electron bremsstrahlung accelerators (Nauka, 1972) with Anton Komar and Igor Lopatin. He had a major impact on the development of both the PNPI High Energy Physics Division and the field of hadron physics at Gatchina and worldwide.

Then he focused on the complete experiment for the pion-nucleon elastic scattering to determine partial-wave amplitudes and parameters of low-laying non-strange nucleon resonances. Sergey lead the effort to build two meson channels on the 1-GeV PNPI proton synchrocyclotron. He supervised the construction of the two main detectors and unpolarized and polarized hydrogen targets used to measure cross sections and polarization observables. Finally, partial-wave analysis technology allowed him to interpret the Gatchina and worldwide data. In 1985, Sergey received his Habilitation on study of elastic pion-nucleon scattering in the region of low-lying pion-nucleon resonances. Later, he was involved in the Crystal Ball activity at BNL to study hadronic physics using both pion and kaon secondary beams. Finally, Sergey returned back to his favorite task physics of the electromagnetic processes using the Crystal Ball at the Mainz Microtron.

Sergey supervised more than 20 Ph.D. students who now work worldwide in many nuclear physics facilities. He was a great mentor and friend; an excellent teacher with infectious enthusiasm, he was a strong supporter of his students. The community will miss him greatly.

William Briscoe, Anatoly Gridnev, Nikolai Kozlenko, Igor Lopatin, Igor Strakovsky, and Victorin Sumachev