Steve's picture

Steven W. Yates

A&S Distinguished Professor

Professor and Chair
Nuclear Chemistry

Office: 125 Chemistry-Physics Building
Phone: (859) 257-7082
FAX: (859) 323-1069

1968 B.S., University of Missouri at Columbia
1973 Ph.D., Purdue University
1973-1975 Postdoctoral Fellow, Argonne National Laboratory
1981-1982 Gastwissenschaftler, Kernforsungsanlage Juelich, Germany
1989-1990 Visiting Scientist, Lawrence Livermore National Laboratory
1997-1998 Guest Scientist, Los Alamos National Laboratory

Awards and Honors

  • 1972-1973 Procter and Gamble Fellow
  • 1981 University of Kentucky Research Foundation Award
  • 1983 ACS Student Affiliates Teacher of the Year
  • 1985 Chairman, Lexington Section, American Chemical Society (ACS)
  • 1987-1989 Councilor, Lexington Section, ACS
  • 1992-1993 University Research Professor
  • 1992 Chancellor's Award for Outstanding Teaching
  • 1992 Chairman, Division of Nuclear Chemistry and Technology, ACS
  • 1993-1994 Distinguished Professor of the College of Arts and Sciences
  • 1994 William B. Sturgill Award for Outstanding Contributions to Graduate Education
  • 1995-2003, 2008-2010 Councilor, Division of Nuclear Chemistry and Technology, ACS
  • 2002 Fellow of the International Union of Pure and Applied Chemistry (IUPAC)
  • 2006 Glenn T. Seaborg Award for Nuclear Chemistry, ACS

For many years it has been recognized that nuclei in certain mass regions exhibit stable deformations, while those in other regions are essentially spherical. The shell model, an independent-particle model, has been used to explain the properties of spherical nuclei by assigning orbitals to each of the neutrons and protons of the nucleus. These orbitals are then filled in order of increasing energy, similar to the "aufbau" process. With this approach, it is possible to understand the exceptional stability of nuclei containing closed shells (or magic numbers), i.e., nuclei composed of 2, 8, 20, 28, 50, 82, and 126 neutrons or protons. In nuclei at or near closed shells, we are examining multiphonon vibrational excitations of quadrupole and octupole types.

Away from these closed shells, collective nuclear motions appear to dominate over independent-particle modes. The best evidence for collective excitations is the rotational nuclear level structure observed for nuclei of the rare earth and actinide regions. Sequences of low-lying states closely obeying the quantum relationship for a rigid rotor occur which are reminiscent of the rotational levels known for diatomic molecules. For such open-shell nuclei, ample evidence has long been available to confirm that these nuclei have an intrinsic prolate shape. In measurements on deformed nuclei, we have sought to identify two-phonon quadrupole states, to characterize "scissors mode" excitations in which the neutrons and protons oscillate independently, and to search for "superdeformed" states.

In addition to searching for new modes of excitation in nuclei, we have focussed on the complex transition between deformed and spherical shapes in our studies at the Accelerator Laboratory at the University of Kentucky. We have extensively utilized the inelastic neutron scattering (INS) reaction and gamma-ray emission spectroscopy to examine many nuclei. INS, coupled with detection of the de-exciting gamma rays, is distinctly superior to other nuclear reactions for the study of low-lying nuclear states. With this method, we can obtain excellent sensitivity for observing weakly excited states, and the INS reaction is not restricted by spin and parity selection rules. We have developed methods for measuring short nuclear lifetimes with the Doppler-shift attenuation method, and gamma-gamma coincidence mceaurements are now performed routinely. We are currently exploiting these unique advantages to examine a variety of structural features of nuclei and to search for new, exotic nuclear modes.