Obituary of Sperry E. Darden

Sperry E. Darden, emeritus professor of physics at the University of Notre Dame, died on 23 October 2009. “Bud”, as he was known to his colleagues, friends, and many admirers, received a bachelor’s degree in physics from Iowa State College and did his graduate work in nuclear physics under the guidance of Prof. Heinz Barschall at the University of Wisconsin. Having interrupted his doctoral studies for a year to serve on the research staff at Los Alamos National Laboratory, Bud was awarded the PhD degree in 1955. He then joined the physics department of the University of Notre Dame which became his research home until his retirement in 1994.

Bud was one of the pioneers in elucidating the role of spin in nuclear physics. Not long after the importance of the nuclear spin-orbit force for the shell model had been discovered he — in close connection with others venturing into this new field such as the University of Basel group — recognized the necessity of studying spin-polarization phenomena in nuclear reactions. Very early on, before the advent of polarized-ion sources on accelerators, he investigated the production of polarization in nuclear reactions, helping to establish the role of the spin-orbit term in the optical model. His development of polarimeters and polarization-measurement techniques made these studies possible. The absolute calibration of deuteron tensor-polarization via the isospin-forbidden ¹⁶O(d,α₁)¹⁴N* reaction, as well as the systematic study of the analyzing power of silicon for use in spin-transfer polarimeters, are examples.

Around 1967, Bud and his collaborators developed one of the first Lamb-shift sources and installed it on the FN tandem accelerator at Notre Dame. Subsequent investigations of the analyzing powers of two-particle and three-particle breakup reactions led to many important publications. His interests had shifted to learning more about nucleon-nucleon forces acting in few-body systems, as well as charge-symmetry breaking. An example is his work on the ⁴He(d,αp)n reaction with tensor-polarized deuterons, in which he measured the transition of the deuteron to the singlet state in the np final-state interaction.

Bud’s venture into more exotic polarization studies included that of heavier nuclei such as ⁶Li, ⁷Li, and ²³Na. The latter two, having spin 3/2, offered additional observables but also required the more complicated formalism of rank-3 polarization tensors and corresponding measurement methods. During a sabbatical in England, he worked on and with a source delivering polarized beams of these nuclei to the Daresbury tandem accelerator. An absolute-polarization calibration point for ²³Na vector polarization via the ²³Na(p,α₁)²⁰Ne* reaction followed from one of his suggestions.

Bud was instrumental in unifying the formalism for describing polarization in nuclear reactions. His suggestions led to the “Madison Convention” for spin-1 particles, adopted at the 3rd International Symposium on Polarization Phenomena. He also treated the case of spin 3/2 such as for ²³Na, and in the process illustrated the shapes and the rotation-, P- and T-transformation properties of tensor moments up to rank 3 by geometrical surfaces. His partly hand-drawn illustrations helped visualize these complicated objects. Bud always had a keen pedagogical interest in elucidating purely formal presentations by some more-elementary treatment, as evidenced by his article on “Polarized Spin-One Particles” in the American Journal of Physics, which certainly helped many students to get acquainted with spin polarization.

In addition to the sabbatical years he spent at the University of Basel and the University of Birmingham, Bud was instrumental in helping to set up a polarized-beam program at the National Center for Nuclear Physics in Mexico. In the process he became fluent in Spanish as well as German, and in his later years undertook a formal study of Russian. An excellent teacher as well as a scholar, Bud was a PhD thesis advisor for 19 students, many of whom became faculty members at universities in the US and other countries. He often told colleagues and friends of his great good fortune in having a career that allowed him to do what he most loved...teaching and research. After retirement, Bud devoted even more time to his second career as a community volunteer: tutoring high-school students, working at a homeless shelter, and setting up a scholarship fund for students at his local parish school were just a few of his many activities until he became disabled by Alzheimer’s disease. He will be sorely missed by those of us fortunate enough to have known this remarkable man.

James J. Kolata, , ,

Hans Paetz gen. Schieck

University of Köln