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Triangle Universities Nuclear Laboratory

Duke University

Box 90308

Durham, NC 27708-0308

Phone: (919) 660-2636

FAX : (919) 660-2643

tonchev@tunl.duke.edu


Professional Experience

2007 to Pres.: Assistant Research Professor at Duke University

2005 to Pres.: Adjunct Associate Professor at Department of Physics and Astronomy at UNC Chapel Hill

2000 to 2007: Senior Research Scientist at Triangle University Nuclear Laboratory, Duke University

1997 to 2000: Research Assistant Professor at Idaho State University

1996: Visiting Scientist at Hahn-Meitner Institute, Berlin, Germany

1988 to 1997: Scientific Worker at Joint Institute for Nuclear Physics, Dubna, Russia

Research Interests

Nuclear Structure

A common future in medium- and heavy-mass nuclei is the prevalence of neutrons over protons resulting in formation of a neutron skin. Concomitant with the development of a neutron skin is the appearance of low energy dipole strength, the so-called pygmy dipole resonance (PDR). Existing of neutron skin adds another new aspect to the dynamics of strongly asymmetric nuclear matter. It has been suggested that the PDR perceived as an excitation of the neutron-rich skin against the symmetric core may be used as a constraint on the neutron skin of heavy nuclei. Besides the genuine importance for nuclear structure physics, skin nuclei are of particular relevance for the nuclear astrophysics. For example, the existence of low-energy excitation modes related to the neutron skins could influence the rapid (r) neutron capture process in low-energy (n,gamma) reactions and, therefore, will affect directly the synthesis of heavy nuclei in stellar environments. More information about the nuclear structure experiments at HIGS facility can be found here. This activity is strengthening by ongoing collaborations with the gamma-ray facilities at the Technical University at Darmstadt (Germany), The Forschungszentrum Dresden-Rossendorf (Germany), University of Cologne (Germany), University of Giessen (Germany), University of Notre Dame, and Konan University (Japan).

Nuclear Astrophysics

A key question in nuclear astrophysics is that of the nucleosynthesis processes that lead to the observed abundances of chemical elements in the universe. About 99% of the heavy elements up to iron can be synthesized by either the slow neutron capture process (s-process) or the rapid neutron capture process (r-process), which contribute in approximately equal parts to the total elemental abundances. However, there are 32 stable nuclei on the neutron-deficient side of the chart of nuclides, the so-called p-nuclei, which cannot be produce by neutron capture. These isotopes, ranging from 50V to 196Hg are produced at very high temperature (2-3 T9) in supernova explosions. Our precision cross sections measurements at the HIGS facility is aimed to quantitatively understand the mechanism of the (gamma,n) (gamma,2n), (gamma,p), and (gamma,alpha) reactions responsible for producing of these p-nuclei. In addition, using the most intense (up to 108 g/s) and monoenergetic (dE/E = 1-3%) photon beams from HIGS facility will allow us to obtain an experimental information necessary to understand the nucleosynthesis of the so-called branching-point isotopes by measuring the inverse reaction channel of the neutron capture. Investigations related to nuclear astrophysics that are performed at HIGS involve the techniques of photon scattering and absorption, photo-activation, and photodisintegration measurements.

Nuclear Applications

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 monoenergetic neutron beams at TUNL 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 transmutation, 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 web-address: http://www.tunl.duke.edu/groups/nnsa/.

Scientific Activity

Thesis (PhD): "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, 06/1995.

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, 08/1988.

Publications: [Journal Articles ] [ Academic Conference ] [ Preprints and Annual Reports ]

Invited [ Seminar Speaker ] and presentations at [ International Conferences]

Edited [ Proceedings]

Teaching [ Courses]

Supervised [ Ph.D. ] and [ REU ] students

Total of [$17,386,533] from grants and external funding as PI or co-PI