Sponsored by the ACS Division of Nuclear Chemistry & Technology
Steven W. Yates, professor of chemistry, physics, and astronomy and currently chair of the department of chemistry at the University of Kentucky, has made contributions in all areas of his profession as a researcher and an educator, as an editor and a writer, and as a member of government and private-sector science panels. This award recognizes him for his groundbreaking studies of multiphonon excitations in atomic nuclei and for the development of techniques for measuring very short nuclear lifetimes.
Yates, 59, received a B.S. degree in chemistry from the University of Missouri, Columbia, in 1968 and a Ph.D. in nuclear chemistry from Purdue University in 1973, where he studied with Patrick Daly.
Following his dissertation work at Purdue, during which he characterized a new class of negative-parity states in transitional nuclei and explained them in terms of the semidecoupled model, he accepted a two-year postdoctoral fellowship at Argonne National Laboratory. While there, he investigated the properties of actinide nuclei, primarily by light-ion-scattering and transfer reactions. These investigations led to meaningful predictions, based on single-particle energies, of the ultimate stability of superheavy elements.
In 1975, Yates moved to the University of Kentucky, where he initiated a program of nuclear structure studies. His early work, with measurements performed at Oak Ridge National Laboratory, included the first observation of the backbending phenomenon in the γ-vibrational band of a deformed nucleus. This discovery was key in describing backbending in terms of rotational band interactions and band crossings.
In the late 1970s, Yates began the experiments for which he is best known at the University of Kentucky's Van de Graaff accelerator. Although the inelastic neutron-scattering reaction, first characterized by Glenn T. Seaborg and his colleagues, had been used by others, Yates can be credited with recognizing and developing the spectroscopic power of this reaction and exploiting its potential.
Yates's studies of multiphonon excitations in spherical and deformed nuclei are his most enduring contributions. The identification of both the K = 0 and K = 4 two-phonon γ-vibrational excitations in a deformed nucleus is a remarkable achievement; however, Yates's efforts to understand the octupole excitations are even more significant. In nuclei near the 82-neutron shell closure, he found early evidence for complete multiplets of quadrupole-octupole coupled states, and his search for two-phonon octupole states led to the identification of the 0+ member of the long-sought two-phonon quartet in 208Pb.
This result provided a textbook example of collective excitations in nuclei and must be regarded as confirming the existence of two-phonon octupole vibrations. His group later provided candidates for two additional members of this quartet. Because these identifications rely on knowledge of electric dipole transition rates, his group then launched a study to understand these transitions in spherical nuclei. This work led to the characterization of perhaps the finest example of weak coupling in nuclei.
Yates's most recent work has focused on determining how persistent quadrupole vibrations are in nuclei. He and his colleagues have characterized complete three-phonon multiplets in several nuclei, and, if four-phonon multiplets still retain their collective character, his group holds promise for identifying these excitations as well.
His contributions in other areas are also notable. In addition to receiving both university- and student-initiated awards for his teaching, he has been a regular contributor of educational articles in the Journal of Chemical Education. He has been involved in ACS's Summer Schools in Nuclear Chemistry since their inception. Ten doctoral and seven master's students working under his direction have received degrees, and he has mentored more than a dozen postdocs.
The award address will be presented before the Division of Nuclear Chemistry & Technology.—Linda Raber