Gary Earl Mitchell

Gary Earl Mitchell, nuclear experimentalist and emeritus professor of physics at North Carolina State University, recipient of the 1997 Jesse Beams research award of the Southeastern Section of the American Physical Society, and 2010 recipient of the Division of Nuclear Physics Mentoring award, passed away peacefully in Brevard, North Carolina, on 15 October 2021. In a research career spanning six decades, he published over 400 papers and mentored a generation of graduate students who went on to fulfilling careers in academia, industry, and national security.

Gary was born on 5 July 1935, in Louisville, Kentucky. He received his undergraduate degree from the University of Louisville, his master’s degree from Duke University, and his PhD with R. H. Davis at Florida State University. He then joined Columbia University and began what was to become a lifelong career in the study of resonances in compound nuclear systems. After six years at Columbia, he joined the faculty of NC State and began a fruitful collaboration with Ed Bilpuch at Duke using the facilities at the newly formed Triangle Universities Nuclear Laboratory (TUNL), exploiting the unprecedented experimental resolution provided by the 3 MeV van de Graaf accelerator.

The initial focus of the work was on determination of the fine structure of analog states. Over a 10-year period, 50 analogue states were observed by proton scattering on targets of masses between 40 and 64, and of mass 92, culminating in a highly cited 1976 Physics Reports review by Bilpuch, Lane, Mitchell, and Moses.

These and later studies provided the first charged-particle data sets of sufficient purity and completeness to test Random Matrix Theory (RMT). Developed by Wigner and Dyson by the early 1960s, RMT was not seriously investigated in any system until the 1970s, when neutron resonance data from Columbia and proton resonance data from TUNL became available. Simple tests confirmed the validity of RMT for both data sets. Further evidence followed in the 1980s, when Oriol Bohigas and others identified the “Nuclear Data Ensemble” and tested several stringent statistical measures. Whereas neutron and proton resonance data provided one “window” to test RMT, another window lies near the ground state. Extensive efforts established nearly complete level schemes for ²⁶Al and ³⁰P that allowed for tests of isospin symmetry breaking on spectral statistics. The analysis found that, as predicted by Dyson, a few percent symmetry breaking has a very large effect. These were the first experimental confirmations that in a densely chaotic system, even a small symmetry breaking can have a big effect.

The manifestation of symmetry violation in a chaotic quantum system was the theme of the TRIPLE collaboration at Los Alamos, where parity violation (PV) in compound nuclear (CN) resonances was studied in heavy nuclei. A factor of million enhancement had been observed in Dubna for PV in the 0.73 eV resonance in ¹³⁹La, but conventional wisdom said no real analysis could be performed because CN wave functions were too complicated. Inverting this logic, David Bowman and Mitchell adopted a purely statistical approach and treated the PV matrix elements as random variables, allowing the strength of PV in nuclei to be established with high precision for the first time. Gary’s unmatched knowledge of compound nuclear phenomena and statistical analyses contributed greatly to the success of the program, summarized by Bowman, Garvey, Johnson, and Mitchell in a 1993 Annual Review of Nuclear and Particle Science article .

Graduate students were full partners in all these discoveries, and students were coauthors on the vast majority of his published papers. Over his career he directed or codirected research for almost 60 PhD dissertations. His collaborators and advisees often commented that he was always willing to sit and talk; his door was always open for visitors, students, and colleagues alike. When asked when he got his work done, the response was “be here every day at 6 a.m.—things are quiet!” In recognition of his role in furthering their careers, his former students established the “Gary E Mitchell Graduate Support Endowment” at NC State.

He enjoyed travel and collaborations with colleagues worldwide, particularly with colleagues in Germany, where he received a Senior Scientist Award from the A. von Humboldt Foundation in 1975 and again in 1997. An early positive mentoring experience with a student from Mongolia led to a longer collaboration and the formation in 2007 of the Mitchell Foundation, a registered nongovernmental organization based in Ulaanbaatar, Mongolia. Formerly known as the Mongolian American Scientific Research Center, the foundation was renamed in 2013 in honor of Gary.