Siegbahn, Kai (1918– )

Swedish physicist who was awarded the Nobel Prize for Physics in 1981 for the development of the use of electron spectroscopy for chemical analysis. He studied the electrons emitted from substances irradiated by X-rays by focusing a narrow beam of X-rays of a single wavelength onto a specimen and measuring the energy spectrum of the ejected electrons. The spectrum showed peaks and troughs which were characteristic of the atoms in the specimen. He shared the Nobel Prize with Nicolaas Bloembergen and Arthur Schawlow.

The position of the peaks in the spectrum were shifted by chemical effects and depended upon the way in which the atoms were linked together to form molecules. By analysing these ‘chemical shifts’, Siegbahn was able to identify the constituents of the specimen. He also worked on a related technique using ultraviolet light.

Kai Siegbahn was the son of Karl Manne Siegbahn who won the Nobel Prize for Physics in 1924.