Kai Siegbahn (born 20.04.1918) — a Swedish experimental physicist, a member of the Royal Swedish Academy of Sciences. The son of M. Siegbahn. Born in Lund. He received the degree of Doctor of Philosophy at the University of Stockholm (1944). In 1942—51 he worked at the Nobel Institute for Physics, in 1951—54 he was professor at the Royal Institute of Technology in Stockholm, and from 1954 at the University of Uppsala and director of the Institute of Physics at the university.
His research was in spectrometry, atomic and molecular physics and physical chemistry. He developed (1946) a spectrometer with double focusing and constructed (1950) a precision spectrometer with a large radius of curvature. He designed the first X-ray electron spectrometer and was the first to carry out the monochromatisation of X-rays in X-ray photoelectron spectroscopy. He developed (1951) the method of electron spectroscopy for chemical analysis (ESCA). Using this method he obtained narrow electron spectra whose maxima corresponded to the binding energies of electrons in the inner shells of atoms, and studied the binding energies of electrons in practically all the chemical elements. In 1981 he was awarded the Nobel Prize for his contribution to the development of electron spectroscopy.
From 1981 he has been president of the International Union of Pure and Applied Physics. The A. Celsius Medal (1962). A member of a number of academies of sciences.