Hans Frauenfelder

Hans Frauenfelder (born July 28, 1922) is a Swiss-American physicist and biophysicist. He is known for his discovery of perturbed angular correlation (PAC) in 1951. In the modern day, PAC spectroscopy is widely used in the study of condensed matter physics. 
Frauenfelder was born in Schaffhausen, Switzerland. He studied at ETH Zurich.
Within biophysics, he is known for experiment and theory in understanding the dynamical behavior of protein tertiary structure. In 1992, Frauenfelder won the Max Delbruck Prize.
Frauenfelder is a member of the National Academy of Sciences, the American Philosophical Society, and a Foreign Member of the Royal Swedish Academy of Sciences.