Gencho Rusev, Research Scientist
Office Location: 412 TUNL Building
Office Phone: (919) 660-2636
Email Address: g.rusev@duke.edu
Web Page: http://www.tunl.duke.edu/~rusev/
Specialties:
Experimental nuclear physics
Education:
Dr. Rer. Nat., Technische Universitaet Dresden, Dresden, Germany, 2007
Magister, University of Sofia, Sofia, Bulgaria, 1999
Research Categories: Gamma-ray spectroscopy, Nuclear structure, Gamma-ray strength functions
Research Description: Dr. Rusev's main area of research is the study of the response of atomic nuclei to electromagnetic radiation. It includes the investigation of the statistical properties of the reemitted radiation in connection with nuclear structure and nuclear astrophysics phenomena.
The probability for absorption of a real photon by the nucleus (the photoabsorption cross section) exhibits a strong maximum around 10-20 MeV called the giant dipole resonance (GDR), which is an E1 mode of excitation. Other resonances corresponding to M1, E2, M2, etc. types of excitations, were discovered as well but with much smaller strength than the GDR. The centroid energies and the strength of these resonances depend strongly on the structure of the nucleus. The electromagnetic interaction is the one we understand best, therefore, the investigation of the photoabsorption cross section and a search for new phenomena is important for the development of theoretical models describing the interaction of nucleons.
Current research on the photodisintegration cross section is focused on the low-energy tail of the GDR. The cross section at energies sufficient for the separation of a neutron or other particles is of interest for nuclear astrophysics. There are 35 stable nuclei which cannot be produced in neutron-capture reactions (s- or r-process). Their existence is described as a result of photodisintegration of heavier seed nuclei. For the understanding and modeling of this so-called p-process, the photoabsorption cross section up to and near the particle separation energies has to be known accurately.
Different phenomena observed in the tail of the GDR are of importance for understanding the structure of nuclei. Low-momentum excitation modes like the "scissors mode", "pygmy dipole resonance", two-phonon coupling, etc. triggered the interest of theorists and lead to development of new theoretical models of the nucleus. The HIgS facility at the Duke FEL laboratory is a worldwide leading installation which provides intense, nearly mono-energetic and 100% linearly (or circularly) polarized photon beams suitable for low-momentum transfer experiments needed for nuclear-structure studies. Photon-scattering experiments at HIgS allow assignment of the energy, ground-state width, spin and parity of nuclear levels in a model-independent way, which is important for correct comparison with theoretical predictions.
A particular area of Dr. Rusev's research is devoted to the investigation of the statistical properties of the nucleus as a quantum many-body system. The nuclear system may emit electromagnetic radiation, known as a gamma ray, if its energy (excitation energy) is larger than the minimal possible energy of the system. Depending on the excitation energy, the interpretation of the gamma-ray decay of the nucleus divides, in general, into two directions - deterministic and stochastic. In the deterministic approach, known as gamma-ray spectroscopy, we assign an observed gamma ray to a particular transition between two states in the nucleus. The comparison of the energy and the intensity of the gamma rays with predictions from theory leads to valuable information about the structure of the nucleus, discussed in the paragraph above. Gamma-ray spectroscopy can only be applied to transition energies of a few MeV because of the difficulties theory faces in calculating the correct transition energy. At higher energies, we can no longer associate an observed gamma ray with a transition between two states, but rather we compare the intensity distribution of the measured gamma rays with predictions from theory. The quantity which characterizes the intensity distribution is called gamma-ray strength function or photon-strength function (PSF).
The concept of the PSF and the statistical behavior of gamma rays emitted from a nucleus is the basis for models which predict the dynamics of nuclear cascade transition. Codes based on the Monte-Carlo technique or on the Hauser-Feschbach reaction theory were developed to estimate the gamma-ray rate from a given reaction. There is a large range of applications of such calculations from nuclear astrophysics to the development of new reactors with fast neutrons.
Areas of Interest:
Dipole excitations
Statistical properties of the nuclei
Nuclear structure at high spin
Recent Publications (More Publications) (search)
- L. Atanasova, et al. (including G. Rusev), g-factor measurements at RISING: The cases of 127Sn and 128Sn, Europhysics Letters, vol. 91 (October, 2010), pp. 42001 .
- A. Makinaga, R. Schwengner, G. Rusev, F. Dönau, S. Frauendorf, D. Bemmerer, R. Beyer, P. Crespo, M. Erhard, A. R. Junghans, J. Klug, K. Kosev, C. Nair, K. D. Schilling, and A. Wagner, Dipole strength in 139La below the neutron-separation energy, Phys. Rev. C, vol. 82 (August, 2010), pp. 024314 .
- R. J. deBoer, M. Wiescher, J. Görres, R. Longland, C. Iliadis, G. Rusev, and A. P. Tonchev, Photoexcitation of astrophysically important states in 26Mg. II. Ground-state-transition partial widths, Phys. Rev. C, vol. 82 (August, 2010), pp. 025802 .
- M. Erhard, E. Grosse, A. R. Junghans, J. Klug, C. Nair, G. Rusev, K. D. Schilling, R. Schwengner, and A. Wagner, Photoactivation of the p-nucleus 92Mo with bremsstrahlung at ELBE, J. Phys. Conf. Ser., vol. 202 (July, 2010), pp. 012014 .
- A. Makinaga, G. Rusev, R. Schwengner, F. Dönau, R. Beyer, D. Bemmerer, P. Crespo, M. Erhard, A. R. Junghans, J. Klug, C. Nair, K. D. Schilling, and A. Wagner, Cross section measurement on 139La (g, g') below neutron separation energy, AIP Conf. Proc., vol. 1238 (June, 2010), pp. 228 .