Mössbauer , Rudolph Ludwig

(1929–) German physicist

Born at Munich in Germany, Mössbauer was educated in Munich-Pasing and, after a year in industrial laboratories, studied physics at the Munich Technical University. There he passed his intermediate degree in 1952, and completed his thesis in 1954. From 1955 to 1957 he did postgraduate research at the Max-Planck Institute for Medical Research in Heidelberg, gaining his doctorate from the Technical University in 1958.

From 1953 he had been studying the absorption of gamma rays in matter, in particular the phenomenon of nuclear resonance absorption. Normally, when an atomic nucleus emits a gamma ray, it will recoil, and this recoil action will influence the wavelength of the gamma ray emitted. Mössbauer discovered that, contrary to classical predictions, at a sufficiently low temperature the nucleus can be locked into position in the crystal lattice, and it is the lattice itself that recoils, with negligible effect on the wavelength. The result is that the wavelength can be defined with extremely high precision (about 1 part in 10¹²). As with emission, so it is with absorption; a crystal of the same material under similar conditions absorbs gamma rays at the same highly specific wavelength – a resonance phenomenon akin to a well-tuned radio receiver and transmitter. If, however, the conditions are slightly different, the small changes in wavelength can be accurately compensated and thus measured using the Doppler effect (by moving the source relative to the receiver).

This phenomenon of recoilless nuclear resonance absorption, now known as the Mössbauer effect, has given physicists and chemists a very useful tool through the high precision of measurement it allows. In particular, it allowed the first laboratory testing (and verification in 1960) of the prediction of Einstein's general theory of relativity that the frequency of an electromagnetic radiation (in this case gamma rays) is influenced by gravity. The Mössbauer effect is now commonly employed as a spectroscopic method in chemical and solid-state physics because of its ability to detect differences in the electronic environments surrounding certain nuclei (Mössbauer spectroscopy).

In 1960, after finishing his studies at the Technical University, Mössbauer went on to continue his investigations of gamma absorption at the California Institute of Technology, Pasadena, where he was appointed professor of physics the next year. In 1961 he also received the Nobel Prize for physics, sharing the honor with Robert Hofstadter who had advanced knowledge of the nucleus by electron-scattering methods.