Triangle Universities Nuclear Laboratory
Box 90308
Durham, NC 27708-0308
Phone: (919) 660-2636
FAX : (919) 660-2643
One of my primary focuses at TUNL is directed to using the highly intensive, 100% polarized and monoenergetic gamma-ray source at HIGS. The quality and the quantity of this novel gamma beam from the HIGS facility allows us to have a deeper and more precise view of the mechanism of the nuclear reactions at a broad range of energies from Egamma=1-50 MeV. For instance, the HIGS source was used to measure 150 new parities in deformed and neutron closed-shell nuclei, including 40Ar 88Sr, 92Zr, 96Mo, 112,124Sn, 138Ba, 172,174,176Yb, 164,162Dy, and 208Pb, in inelastic gamma scattering experiments. In this project, our focus is the study of the different modes of excitation at energies below the neutron threshold. These include two-phonon excitations of even-even, nearly closed shell nuclei with large magnetic dipole (M1) strength, the "scissors mode". Large electric dipole (E1) transitions to the ground states have been observed in spherical nuclei near Z = 50 and N = 82, which are assumed to arise from the coupling of quadrupole and octupole vibrational modes of the nucleus. Recent experiments at HIGS were aimed to study the Pygmy Dipole Resonances, described as a clustering of states close to the neutron threshold at excitation energies from 5.5 MeV to 8.0 MeV. Although carrying only a small fraction of the full dipole strength, these states are of particular interest because they reflect the motion of the neutron skin against the isotopic symmetric core. The very recent experimental results on N=82 nuclei were able to unveil a dipole strength which was not seen in from the previous nuclear resonance fluorescent experiments. The strength at the neutron separation energy, for example, is 5 times larger than the strength to the ground state. The total Pygmy strength is not only an interesting nuclear structure phenomenon, but also can affect the synthesis of nuclei in explosive stellar burning phases and the photodisintegration of ultra-high-energy cosmic rays. These measurements have started a renaissance of the traditional nuclear resonance spectroscopy and opened a new chapter in experimental approach to nuclear structure and nuclear astrophysics. More information about the nuclear structure experiments at HIGS can be found here. This activity is strengthening by ongoing collaborations with the gamma-ray facilities at the Technical University at Darmstadt (Germany), Konan University (Japan), University of Cologne (Germany), University of Giessen (Germany), and MSU.
Another direction, which I am strongly involved at TUNL, is establishing an experimental program to study (n,2n) excitation functions on Actinide nuclei using monoenergetic and pulsed neutron beams. Key instruments for this research include the ion sources and associated accelerator for generating neutron beam at TUNL which produces the world's most intense and highly polarized monoenergetic neutron beams in the low-energy regime. The source, in combination with cutting-edge detector systems like two-fold segmented Clover HPGe detectors, offers new insights into nuclear systems. In parallel, application-oriented research is pursued in nuclear transmutations, biophysics and nuclear medicine. Measurements have been performed on 235,238U and 241Am targets, with incident neutron energies ranging from 4 to 18 MeV. The goal is to improve the partial cross section data in the fast neutron spectra in order to reduce the calculation uncertainties associated with the nuclear data. The nuclear data measurements are expected to have a significant impact on solving the nuclear energy problem. More detailed information about this project can be found on the following NNSA web-address.
Also I am also interested in the study of the nuclear structure (isomeric states, giant resonance, deformed and hyperdeformed states, alpha particle clustering), nuclear dynamics (nuclear fission, gamma and particle emission, transition from chaos to order) and high-spin isomeric targets production.
PhD thesis: "Investigation of Isomeric States in Photonuclear Reactions in the Giant Dipole Resonance Region", Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia, June, 1995.
Diploma work: "Photonuclear Reactions and their application in Photo Activation Analysis", University of Plovdiv, Plovdiv, Bulgaria and Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia, August, 1988.
Publications: [Journal Articles ] [ Academic Conference ] [ Preprints and Annual Reports]
Recent Invited Presentations at [ International Conferences]
Edited [ Proceedings]
Teaching [ Courses]
Current [ Ph.D. Students ] supervising
