Mitrofan Vasilyevich Pasechnik (born 17.06.1912) is a Soviet physicist and an academician of the Academy of Sciences of the Ukrainian SSR (1961). Born in Zhirkovka (now in Poltava Region). Graduated from the Poltava Institute of Social Education (1931). In 1932–40 and 1946–70 he worked at the Institute of Physics of the Academy of Sciences of the Ukrainian SSR (director in 1949–65). From 1970 he has worked at the Institute for Nuclear Research of the Academy of Sciences of the Ukrainian SSR (director in 1970–73). In 1947–60 he was also head of a department at Kiev University.
His work was devoted to nuclear physics, reactor physics, metal physics, and the history and methodology of physics. He studied the structure of alloys and protective layers by electron diffraction, and the interaction of nucleons of low and medium energies with atomic nuclei. He carried out a set of studies of the interactions of fast and slow neutrons with nuclei, connected with the creation of fast-neutron reactors, and obtained data pointing to the existence of isotopic-spin and shell effects in spherical and deformed nuclei. Together with others he discovered isotopic effects in the elastic scattering of protons. He carried out a series of works on determining neutron constants and the radiation resistance of the main structural materials of nuclear reactors.