NOBEL PRIZE IN PHYSICS 1924, MANNE SIEGBAHN, WITH DIPLOMA; NOBEL PRIZE IN PHYSICS 1981, KAI SIEGBAHN WITH DIPLOMA
- Nobel Prize of Physics medal awarded to Manne Siegbahn for his discoveries and research in the field of X-ray spectroscopy, and the Nobel Prize for Physics awarded to his son Kai Siegbahn for his contribution to the development of high-resolution electron spectroscopy
- gold, vellum,
Manne Siegbahn and his son Kai Siegbahn were both pioneers in spectroscopy, the study of the interaction between matter and electromagnetic radiation. It is a field that was of enormous importance to the development of atomic physics. The most significant and exciting work in physics of the early twentieth century laid the foundations of Quantum Mechanics and dealt with particles and phenomena of incredibly small size. Not only were the new theories of Planck, Bohr, Einstein, and others of enormous intellectual ambition, they were exceptionally difficult to prove as subatomic particles largely resisted direct observation. Spectroscopy allowed access to the strange world of subatomic particles by measuring their traces, the distinct patterns of radiation emitted by different atoms.
Manne Siegbahn (1886-1978) was educated at the University of Lund. When researching for his doctorate (which he received in 1911) he came under the influence of the mathematical physicist Janne Rydberg, who was fascinated by the relationship between the spectral lines of atoms and their place in the Periodic Table. In the early 1910s it was becoming clear that there was a correlation between an atom’s atomic number and its X-ray emission spectrum. This held out the possibility of whole new avenues of research – if only the patterns of emissions could be studied with sufficient accuracy. It was precisely in the development of high-precision spectrography that Manne Siegbahn excelled. His improved spectrographs enabled the wavelengths of X-rays to be determined with new accuracy, leading to a series of breakthroughs in the 1910s and early 1920s. He discovered the “M-series” of X-rays in 1916, whilst the modelling of atoms’ electron shells made possible by his observations confirmed the ideas on atomic structure postulated by Nils Bohr and others. Siegbahn’s observations of atomic structure therefore laid down the empirical foundation for Quantum Theory.
In 1922 Siegbahn left Lund for Uppsala, where he was appointed Professor of Physics. In the 1930s he became increasingly drawn to nuclear physics, especially following Chadwick’s discovery of the Neutron in 1932, and in 1937 he moved to Stockholm as the founding director for the Nobel Institute of the Royal Swedish Academy of Science, a national centre for nuclear physics. Siegbahn’s laboratory provided a home for a number of scientists during the tumultuous years around World War II, the most prestigious being Lise Meitner, the Jewish physicist who, with Otto Hahn, first discovered nuclear fission.
Manne Siegbahn was awarded the Nobel Prize in unusual circumstances. None of the 23 nominations for the Physics Prize in 1924 were deemed worthy of the award, so when Siegbahn was nominated in 1925 he was retrospectively awarded the previous year’s still-open prize. His Nobel lecture eloquently explained why X-rays were at the heart of his work:
“It is obvious that the fact that X-rays are such an important tool for workers in various fields of science forms a very cogent reason for undertaking a thorough investigation of their nature. It is also clear that, seen from this viewpoint, any investigation of X-radiation must be planned on a broad basis, and cannot be directed solely towards the more or less specialized problems affecting different branches of science.
The study of X-rays is not, however, motivated only by their application in the various sciences we have just mentioned. X-rays provide us in addition with an insight into the phenomena within the bounds of the atom. All the information on what goes on in this field of physical phenomena is, so to speak, transmitted in the language of the X-rays so it is a language which we must master if we are to be able to understand and interpret this information properly.”
Manne Siegbahn’s younger son, Kai (1918-2007) followed him into the world of physics. He took his doctorate at the University of Stockholm in 1944 and worked at his father’s research institute from 1942 to 1951. In 1954 he was appointed to a Professorship in experimental physics at Uppsala – the same chair, in fact that his father had held until 1937 – where he remained for thirty years. He was also a member of the Royal Swedish Academy of Sciences. When the Academy began their deliberations for the award of the 1981 prize he was asked to absent himself; in that year he followed his father in being awarded the Nobel Prize for Physics.
Kai Siegbahn’s breakthrough research was in X-ray photoelectron spectroscopy or XPS (also known as electron spectroscopy for chemical analysis or ESCA). This technique makes use of the photoelectric effect (explained by Einstein in his 1905 paper using a quantum-based theory that won him the Nobel Prize in 1921), by which atoms emit electrons (photo-electrons) when light shines on them. Atoms can be identified by their energy level, which can be measured through the energy levels of the electrons that those atoms emit when irradiated with photons. Like his father, Kai Siegbahn’s genius was experimental: laboratory experiments had measured the emission of electrons as early as 1907, but in the post-war years Kai Siegbahn made radical improvements that enabled emissions of photo-electrons to be measured with unprecedented accuracy. Kai Siegbahn transformed the technique of XPS from a laboratory curiosity into an exceptionally important analytic tool, overcoming the exceptional challenges in mapping the shape of such tiny emissions with sufficient accuracy that they could be meaningfully interpreted.
XPS is a powerful tool that has proved to have a remarkably wide range of applications, not only in the growing field of surface science but also in industry. Not only does it allow us to identify which elements are present in a sample, but it can also, for example, detect the presence of any contamination of surfaces and establish the thickness of distinct layers within the top few nanometres of a surface. Semiconductors, medical implants, even paints and make-up, are all regularly subjected to XPS.