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 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 states, to characterize "scissors mode" excitations in which the neutrons and protons oscillate independently, and to search for other exotic modes.

In addition to searching for new degrees of freedom 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, low-spin 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.

Awards and Honors

• 1972-1973 Procter and Gamble Fellow
• 1981 University of Kentucky (UK) Research Foundation Award
• 1983 Student Affiliates of the American Chemical Society (SAACS) Teacher of the Year
• 1985 Chairman, Lexington Section of the American Chemical Society (ACS)
• 1987-1989 Councilor, Lexington Section of ACS
• 1992-1993 University Research Professor, UK
• 1992 Chancellor's Award for Outstanding Teaching, UK
• 1992 Chairman, Division of Nuclear Chemistry and Technology, ACS
• 1993-1994 Distinguished Professor of the College of Arts and Sciences, UK
• 1994 William B. Sturgill Award for Outstanding Contributions to Graduate Education, UK
• 1995-2003, 2008-2010 Councilor, Division of Nuclear Chemistry and Technology, ACS
• 2002 Fellow of the International Union of Pure and Applied Chemistry (IUPAC)
• 2005-2009 Chair, Department of Chemistry, UK
• 2006 Glenn T. Seaborg Award for Nuclear Chemistry, ACS
• 2008-present, Arts and Sciences Distinguished Professor, UK
• 2009 Fellow of the American Chemical Society

• E. Elhami, J. N. Orce, S. Mukhopadhyay, S. N. Choudry, M. Scheck, M. T. McEllistrem, and S. W. Yates, “Anomalous Behavior of the 2⁺ Mixed-Symmetry State in ⁹⁴Zr”, Phys. Rev. C 75, 011301(R), 2007.
• J. N. Orce, C. Fransen, A. Linnemann, C. J. McKay, S. R. Lesher, N. Pietralla, V. Werner, G. Friessner, C. Kohstall, D. Mücher, H.H. Pitz, M. Scheck, C. Scholl, F. Stedile, N. Warr, S. Walter, P. von Brentano, U. Kneissl, M. T. McEllistrem, and S. W. Yates, “Lifetime measurements in ⁹³Nb from photon and inelastic neutron scattering”, Phys. Rev. C 75, 014303 (2007).
• S. R. Lesher, C. J. McKay, M. Mynk, D. Bandyopadhyay, N. Boukharouba, C. Fransen, J. N. Orce, M. T. McEllistrem, and S. W. Yates, “Study of the Low-Spin Structure of ⁹⁶Mo with the (n,n'γ) Reaction”, Phys. Rev. C 75, 034318 (2007).
• M. Scheck, P. von Brentano, C. Fransen, U. Kneissl, C. Kohstall, A. Linnemann, D. Mücher, N. Pietralla, H. H. Pitz, C. Scholl. F. Stedile, S. Walter, V. Werner, and S. W. Yates, “Dipole Strength Distributions of the Stable odd-mass N = 82 isotones ¹³⁹La and ¹⁴¹Pr”, Phys. Rev. C 75, 044313 (2007).
• P. E. Garrett, K. L. Green, H. Lehmann, J. Jolie, C. A. McGrath, M. Yeh, and S. W. Yates, “Properties of ¹¹²Cd from the (n,n'γ) Reaction: Lifetimes and Transition Rates”, Phys. Rev. C 75, 054310 (2007).
• J. N. Orce, S. N. Choudry, B. Crider, E. Elhami, S. Mukhopadhyay, M. Scheck, M. T. McEllistrem, and S. W. Yates, “2₁⁺ → 0₁⁺ Transition Strengths in the Sn Nuclei”, Phys. Rev. C 76, 021302(R) (2007); Phys. Rev. C 77, 029902(E) (2008).
• S. R. Lesher, J. N. Orce, Z. Ammar, C. D. Hannant, M. Merrick N. Warr, T. B. Brown, N. Boukharouba, C. Fransen, M. Scheck, M. T. McEllistrem, and S. W. Yates, “Study of 0⁺ Excitations in ¹⁵⁸Gd with the (n,n'γ) Reaction”, Phys. Rev. C 76, 034318 (2007).
• D. Bandyopadhyay, S. R. Lesher, C. Fransen, N. Boukharouba, P. E. Garrett, K. L. Green, M. T. McEllistrem, and S. W. Yates, “An Investigation of Phonon Excitations in ¹¹⁴Cd with the (n,n'γ) Reaction”, Phys. Rev. C 76, 054308 (2007).
• I. Ahmad, F. G. Kondev, Z. M. Koenig, W. C. McHarris, and S. W. Yates, “Two-quasiparticle states in ²⁵⁰Bk studied by Decay Scheme and Transfer Reaction Spectroscopy”, Phys. Rev. C 77, (2008).
• J. N. Orce, S. N. Choudry, B. Crider, E. Elhami, S. Mukhopadhyay, M. Scheck, M. T. McEllistrem, and S. W. Yates, “2₁⁺ → 0₁⁺ Transition Strengths in the Sn Nuclei,” Phys. Rev. C 76, 021302(R) (2007), Phys. Rev. C 77, 029902(E) (2008).
• J. N. Orce, B. Crider, S. Mukhopadhyay, E. Peters, E. Elhami, M. Scheck, B. Singh, M. T. McEllistrem, and S. W. Yates, Determination of the 2₁⁺ → 0₁⁺ Transition Strengths in ⁵⁸Ni and ⁶⁰Ni,” Phys. Rev. C 77, 064301 (2008).
• W. D. Kulp, J. L. Wood, P. E. Garrett, C. Y. Wu, D. Cline, J. M. Allmond, D. Bandyopadhyay, D. Dashdorj, S. N. Choudry, A. B. Hayes, H. Hua, M. G. Mynk, M. T. McEllistrem, C. J. McKay, J. N. Orce, R. Teng, and S. W. Yates, “Search for Intrinsic Collective Excitations in ¹⁵²Sm,” Phys. Rev. C 77, 061301(R) (2008).
• M. Scheck, S. N. Choudry, E. Elhami, M. T. McEllistrem, S. Mukhopodyay, J. N. Orce, and S. W. Yates, “Pauli blocking in the  low-lying, low-spin states of ¹⁴¹Pr,” Phys. Rev. C 78, 034302 (2008).
• S. Mukhopadhyay, M. Scheck, B. Crider, S. N. Choudry, E. Elhami, E. Peters, M. T. McEllistrem, J. N. Orce, and S. W. Yates, “Multiphonon states in ¹³⁶Ba”, Phys. Rev. C 78, 034317 (2008).
• E. Elhami, J. N. Orce, M. Scheck, S. Mukhopadhyay, S. N. Choudry, M. T. McEllistrem, S. W. Yates, C. Angell, M. Boswell, B. Fallin, C. R. Howell, A. Hutcheson, H. J. Karwowski, J. H. Kelly, Y. Parpottas, A. P. Tonchev, and W. Tornow, “Experimental study of the low-lying structure of  ⁹⁴Zr with the (n,n'γ) reaction,” Phys. Rev. C 78, 064303 (2008).
• S. F. Hicks, J. R. Vanhoy, and S. W. Yates, “Fragmentation of Mixed-Symmetry Excitations in Stable Even-Even Te Nuclei,” Phys. Rev. C 78, 054320 (2008).