Rolf M. Steffen, a retired professor of physics at Purdue University and an experimental physicist known for his research in nuclear and muon physics, died on 2 October 2000 in Santa Fe, New Mexico, from complications following cancer surgery.

Rolf was born on 17 June 1922 in Basel, Switzerland. He earned his bachelor’s degree in physics from the Swiss Federal Institute of Technology in 1943 and his PhD in physics from the institute in 1948. He joined the Purdue faculty as an assistant professor of physics in 1949.

A leader in the development of angular correlation techniques for nuclear research, Rolf made major contributions to both theory and experiment in this field from 1950 to the mid-1970s. He used many different experimental techniques, including gamma–gamma and beta–gamma angular correlations, gamma-ray angular distributions from oriented nuclei, gamma-ray circular polarization, and beta particle transverse polarization. He studied nuclear structure, time and parity conservation, and the effect of electric and magnetic fields of atoms on nuclei.

In 1969, Rolf became the founding director of the Purdue Nuclear Accelerator Laboratory. He initiated a program using the laboratory’s FN Tandem van de Graaff accelerator for in-beam gamma-ray spectroscopy following heavy-ion fusion reactions. The objective was to investigate the transition from spherical to deformed nuclei that occurs as the nucleon number is increased. Systematic studies were performed on molybdenum, technetium, ruthenium, palladium, silver, and cadmium nuclei. Previous studies had suggested that vibrations were the primary mode of excitation in those nuclei. However, the experiments showed that rotational modes of excitation were much more important than vibrational modes. In fact, the transition from spherical to deformed nuclei could be interpreted as a simple increase in deformation of a slightly deformed symmetric rotor.

Rolf wrote 22 review articles on angular correlation techniques, including major contributions to Alpha-, Beta- and Gamma-Ray Spectroscopy (North-Holland, 1964); The Electromagnetic Interaction in Nuclear Physics (North-Holland, 1975); and the 1970 Los Alamos National Laboratory (LANL) report Angular Distributions and Correlations of Radiation Emitted from Oriented Nuclei. His articles are considered the authoritative resources for scientists working in this area. He was often invited to share his knowledge about angular correlation techniques and taught intensive short courses in Argentina, Japan, Russia, Poland, India, and the UK. He also was a popular seminar speaker. For example, in 1973, he presented seminars in Japan, Germany, Poland, Switzerland, Denmark, the UK, and the US, two or more times in each country.

From 1965 to 1990, Rolf served as a consultant in basic research for LANL. He did research in collaboration with LANL staff and Purdue graduate students. The collaboration used muonic atoms to study the systematics of nuclear charge radii and quadrupole and hexadecapole moments of heavy deformed nuclei. This work yielded a precise understanding of the importance of nuclear shell structure and deformation on these nuclear properties.

Rolf was a gifted and innovative experimentalist whose measurements were state-of-the-art. He supervised 17 doctoral students at Purdue and had a major impact on hundreds of others through his publications, seminars, and personal contacts. He was generous with his time and shared his vast knowledge with anyone who asked him to do so. He also was an excellent leader as a science administrator. Although he loved to do research himself, he spent much of his time enabling research colleagues and students to be successful. He often used less than his share of research funds so that his colleagues would have more to use.

Rolf shared his interests in music, art, culture, and life in general with everyone he knew. His home was like an art museum and concert hall: a joyful place, filled with delightful conversation. His many students, colleagues, and friends are very sad to lose him, but deeply grateful for all the ways he enriched their lives.

Rolf M. Steffen