Robert M. Brugger

Robert M. Brugger, a leader in neutron cross-section measurements, slow-neutron scattering studies of condensed matter, research reactor development, and medical applications of neutron sources, died peacefully on 2 January 2022 at his home in Ashland, Oregon.

Bob was born 13 January 1929 in Oklahoma City. At an early age, he moved to Colorado Springs, where he attended public schools. After earning a BA at Colorado College in 1951, Bob attended Rice University, where he received his MA and PhD under the direction of T. W. Bonner and began using neutrons for both fundamental research and various applications. The first phase of his research involved measuring slow neutron thresholds in (p,n) reactions to determine neutron cross sections and the level structure of stable isotopes using Rice’s van der Graaff accelerators as neutron sources. Neutrons were his tool for the rest of his career.

After receiving his PhD at Rice in 1955, Bob accepted a position at the National Reactor Testing Station (NRTS, now Idaho National Laboratory), where he continued his neutron cross-section measurements using the Materials Testing Reactor (MTR). Some of his cross-section measurements appear in the “Barn Book.”

At the MTR, Bob’s research shifted to slow-neutron inelastic scattering measurements. He designed and built a phased-chopper velocity selector, the first of several, to measure inelastic neutron scattering spectra to reveal the dynamics of molecular systems as well as to explain the thermalization of slow neutrons. This work led to measurements of several sets of dispersion relations of single crystals and the low-lying vibrational states of a number of molecules. In addition, he developed several time-of-flight instruments to measure neutron diffraction patterns of powdered materials for determination of their crystal structure at high pressure. Bob was also called on for his management skills and concluded his stay in Idaho as head of the Nuclear Technology Division at the NRTS.

In 1974 Bob accepted the position of director of the University of Missouri Research Reactor (MURR), which had just increased its power from 5 to 10 MW. At MURR he encouraged development of a small-angle neutron scattering spectrometer, a position-sensitive detector diffractometer for powder neutron diffraction, and a gamma-ray spectrometer. He also played a major role in development of the reactor for commercial applications. For example, he directed efforts to increase the specific activity of molybdenum-99 being produced at MURR for Mo–Tc medical generators. A number of other radioisotopes were developed and made at MURR. Also, under his watch, MURR developed techniques for irradiating single-crystal silicon used in fabricating Si power diodes for the electronics industry. This activity became a major income source for MURR. As MURR grew, Bob showed an early concern for its environmental impact by championing the heating of an addition to the facility with waste heat from the reactor.

While director of MURR, Bob continued research as adviser of nuclear engineering and physics department graduate students, leading to nine MS and eight PhD degrees. These activities included development of several filters to produce monoenergetic neutron beams, neutron Doppler effect measurements, neutron-transmission-computed tomography, prompt gamma neutron activation analysis, and mirror reflection of neutrons at energies of nuclear resonances.

Bob stepped down as director of MURR in 1989, retired from the university in 1991, spent over a year at the medical department of Brookhaven National Laboratory (BNL), and concluded his scientific career as a consultant designing a neutron beam for Neutron Capture Therapy (NCT).

NCT was a recurring interest of Bob’s. Starting at the NRTS, continuing through his tenure at MURR and BNL, and as a consultant at the McClellan reactor, he worked on developing NCT for the treatment of brain cancers. His design contributions led to the first practical epithermal neutron beam at a reactor source for medical applications, which he implemented at the BNL medical reactor. His work also showed the potential of gadolinium-157 as an effective neutron-absorbing isotope for NCT.

Bob’s scientific achievements were recognized by fellowship in the American Physical Society and in the American Nuclear Society (ANS). In 1990 he received the ANS Meritorious Performance Award for Reactor Operations. Beyond his own scientific accomplishments, Bob’s natural abilities as a leader had a profound effect on those around him. He was genuinely curious, modest, and showed utmost respect for the accomplishments and feelings of others. At MURR, he projected a scientific vision at an early stage in its growth that recognized the importance of neutron scattering experimentalists interacting with theorists and the benefits of international collaboration. By his own achievements, leadership, and straightforward manner, he leaves all who worked with him a model to emulate.