Karl Manne Siegbahn. Historical portrait of the Swedish physicist Karl Manne Georg Siegbahn (1886- 1978). Siegbahn worked in X-ray spectroscopy from 1914, discovering a third (M) set of lines in X- ray emission spectra, corresponding to new X-rays with different energies to other X-rays. These lines provided further evidence for Bohr's shell model of the atom, where X-rays are produced by the excitation of electrons from shells within atoms. The shells would be labelled using this K- L-M-N-O-P-Q series. Siegbahn also made advances in the field of X-ray diffraction, used to determine crystal structures. He was awarded the 1924 Nobel Prize for Physics for his X-ray spectroscopy work.