[en] The main topics of the 2014 Workshop: nuclear structure and reactions; symmetries and dynamics; collective and intrinsic motions of nuclei; exotic nuclei; few-body and many-fermion systems; nuclear astrophysics and related topics are part of the NTL’s program for basic nuclear physics research. This broad range of subjects gives a space for the participants to cover the most actual points of view relating the theory with experiment, providing interpretation and predictions, bridging interdisciplinary topics related to nuclear structure and reactions. The Workshop was attended by 42 participants from 19 scientific institutions of 11 countries

[en] The Thirtieth Anniversary International Workshop on Nuclear Theory was held between 27 June and 2 July 2011 in Rila Mountains, Bulgaria. The main topics of the program were: nucleon-nucleon correlation effects on nuclear structure and reactions; symmetries in nuclear structure; collective and intrinsic motions of nuclei; exotic nuclei; few-body systems; advanced studies of many-fermion systems; nuclear astrophysics and related topics. They are related to the problems contained in the research plan of the Nuclear Theory Laboratory of the Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences. The Workshop was attended by 49 participants (including the organizers) from France, Germany, Greece, Italy, Japan, Kazakhstan, Romania, Russia, South Africa, Spain, USA and Bulgaria. The scientific program contained totally 32 oral talks. The schedule of the Workshop was organized so as to provide an opportunity for meetings and discussions among scientists with common interests as well as among physicists working in different fields of research. The secluded mountain area and the lovely forest venue allowed the participants to concentrate on their scientific work but also to refresh between the sessions and get an inspiration for future work development

[en] The 34th volume of the Nuclear Theory series contains articles based on the presentations given at the Thirty Fourth International Workshop on Nuclear Theory (IWNT-34) held from 21st to 27th of June 2015 in the Rila Mountains, Bulgaria. The main topics of the 2015 Workshop were: nuclear structure and reactions; symmetries and dynamics; collective and intrinsic motions of nuclei; exotic nuclei; few-body and many-fermion systems; nuclear astrophysics and related topics are part of the NTL’s program for basic nuclear physics research. This broad range of subjects gives a space for the participants to cover the most actual points of view relating the theory with experiment, providing interpretation and predictions, bridging interdisciplinary topics related to nuclear structure and reactions. The Workshop was attended by 25 participants (including the organizers) from 11 scientific institutions of 7 countries: Belgium, Bulgaria, Italy, France, Kazakhstan, Romania and Russia. The scientific program contained totally 16 oral talks and 3 posters

[en] The main topics of the 2013 Workshop were: Nuclear structure and reactions; Symmetries and dynamics; Collective and intrinsic motions of nuclei; Exotic nuclei; Few-body and many-fermion systems; Nuclear astrophysics and related topics. Most of them are part of the NTL’s program for basic nuclear physics research. However, they were kept open for participants from a much broader area of interests bridging with novel experimental developments, interdisciplinary topics related to nuclear structure and reactions, as well as, nuclear physics applications like nuclear safety. For the first time we had a participant from the Kozloduy Nuclear Power Plant as well as a lecturer giving a talk on nuclear reactor safety. The Workshop was attended by 42 participants (including the organizers) from India, Italy, Germany, UK, Hungary, Poland, Spain, Russia, Kazakhstan, Uzbekistan, South Africa, USA and Bulgaria. The scientific program contained totally 30 oral talks and 1 poster

[en] Full text: Considerable progress has been achieved recently in the experimental investigation of quadrupole-collective isovector excitations in the valence shell, the so called mixed-symmetry states (MSSs), in the mass A ≈ 130 region. This is due to a new experimental technique for study MSSs which is based on the observation of low-multiplicity γ-ray events from inverse kinematics Coulomb excitation with the large 4π spectrometer Gammasphere. Using this technique we have studied all stable cerium and xenon isotopes with N < 82. The obtained experimental information show that for low-collective vibrational nuclei the underlying single-particle structure can be the most important factor for preserving or fragmenting the MSSs. The observed fragmentation of MSSs in "1"3"8Ce and "1"3"6Ce is attributed to the lack of shell stabilization at the proton 1g_7_/_2 sub-shell closure. The evolution of the MSSs from "1"3"4Xe to "1"3"8Ce shows that the separation in energy between the fully-symmetric 2"+_1 state and the 2"+_1_,_m_s level increases as a function of the number of proton pairs outside the Z = 50 shell closure. This behavior can be understood as resulting from the mixing of the basic proton and neutron one quadrupole phonon excitations of the nuclear two-fluid quantum system. It provides the first experimental estimate of the strength of the proton-neutron interaction derived from states with symmetric and antisymmetric nature. The method, the experimental results, and their consequences will be discussed together with future perspectives for the investigation of MSSs in the mass A ≈ 130 region. (author)

[en] Full text: The inversion of the two signatures of a rotational band is considered as an indicator of the nuclear shape [1]. This phenomenon is studied systematically in the odd-odd "1"3"6La and its neighbours, where a positive parity πh_1_1_/_2 ⊗ νh_1_1_/_2 yrast band are known. These nuclei are soft with respect to the triaxiality parameter γ and take a variety of shapes due to the competition of the shape driving forces of the valence h_1_1_/_2 quasineutron and h_1_1_/_2 quasiproton. References: [1] R. Bengtsson, H. Frisk, F.R. May and J. A. Pinston, Nuclear Phys A 415, 189-214, (1984). (author)

[en] Multiply charged isoelectron Helium ions in high-temperature astrophysics and laboratory plasma possesses specific properties and characteristics caused by the noncompensated by electrons long-range Coloumb field of the nuclei. When the ion charge z increases, the relativistic effects role rapidly rises. The LS coupling turns into j − j coupling through area where these two couplings are equally probable - complex coupling. The mass polarization effects become less, but the role of the mass corrections is the same, ensuring the accuracy of the numerical results. The strong Coloumb field determines possibility one or two electrons to occupy highly excited quasidiscrete (autoionized) states, outside the ionization limit. There are two decomposition channels of the excited ion: autoionization and radiation. In that case one can observe several resonance processes, for example electron transition in bound (excited or ground) state with photon emission - radiative recombination (RR) and the opposite process - photoionization. In the case of electron capture the decomposition channels of double excited ion are two also: autoionization and radiation. Radiation decomposition is also possible to realize several resonance processes, depending on the energy electron capture. In the case of electron ”observer” the transition of ion’s electron from free to bound (excited or ground) state is accompanied by so called satellite lines in the spectrum. In the case of interaction with electron having the appropriate resonance energy, there is electron capture and simultaneous ion excitation. The radiative decomposition of double excited ion realizes by photon emission and electron transition into bound (excited or ground) state - dielectronic recombination (DR). In order to investigate the multiply charged ions in high-temperature plasma, theoretical calculations should account relativistic effects, but studying the scattering effects are solved applying non-relativistic approaches: the deformed waves method, strong coupling method, which at Z → ∞are leading to the classical Born-Coloumb approximation with exchange. The applying of these methods in the approaches for plasma diagnostic requires using of precise values for the energetic quantities of the final non-relativistic bound electron states. Then the resonance energy of the interacting electron is possible to be estimated. The proposed work presents ground state electron energies, mass corrections and mass polarization effects of He isoelectronic ions with nuclear charge for the main nuclides from Z = 2 to Z = 118. The developed analytical and numerical method in the Explicitly Correlated Wave Functions approach gives high accuracy of the numerical results, which allows direct application in precise approaches for plasma diagnostics. The dependence of the obtained energies versus Z is investigated, as well as the relative and complex contributions of mass corrections and mass polarization effects in formation of the nonrelativistic and relativistic ground state electron energies. The role of the mass polarization effects is investigated for transition from LS coupling, though complex coupling, to j − j coupling. (author)

[en] A microscopic approach to calculate the optical potential (OP) with the real part obtained by a folding procedure and with the imaginary part inherent in the high energy approximation is applied to study the "6","8He+p elastic scattering data at energies of tens of MeV/nucleon (MeV/N). The OP’s and the cross sections are calculated using different models for the neutron and proton densities of "6","8He. The role of the spin-orbit potential and effects of the energy and density dependence of the effective NN forces are studied. Comparison of the calculations with the available experimental data on the elastic scattering differential cross sections at beam energies < 100 MeV/N is performed and conclusions on the role of the aforesaid effects are made. It is shown that the present approach, which uses only parameters that renormalize the depths of the OP, can be applied along with other methods like that from the microscopic g-matrix description of the complex proton optical potential.

[en] Full text: The structure of the ΔI = 1 doublet bands in doubly odd nuclei from the A ∼ 130 mass region is investigated within the orthosymplectic extension [1] of the Interacting Vector Boson Model (IVBM). A new, purely collective interpretation of these bands is given on the basis of the obtained boson-fermion dynamical symmetry of the model. The model calculations are performed for three odd-odd nuclei, namely "1"2"6Pr, "1"3"4Pr and "1"3"2La [2]. The theoretical predictions for the energy levels of the doublet bands as well as the E2 and M1 transition probabilities between the states of the yrast and yrare bands are compared with experiment and the results of other theoretical approaches. The obtained results reveal the applicability of the used orthosymplectic dynamical symmetry of IVBM. References: [1] H. G. Ganev, J. Phys. G: Nucl. Part. Phys. 35, 125101 (2008). [2] H. G. Ganev, A. I. Georgieva, S. Brant, and A. Ventura, Phys. Rev. C 79, 044322 (2009). Rila. (author)

[en] Full text: The equation-of-state (EoS) of nuclear matter as a function of density and temperature, its composition and the possible occurrence of phase transitions or condensates are widely discussed topics not only in nuclear physics, but are also of great interest in astrophysics and cosmology. Since many of the systems of interest, e.g. exotic nuclei, neutron stars, and supernovae, have large charge asymmetries and exist at very different densities, the density dependence of the symmetry energy is of particular interest. We therefore aim at formulating an EoS which is valid from very low to several times nuclear saturation density and for temperatures up to several tenth of MeV. A particular emphasis is put on the inclusion of light clusters, which are of importance at low densities. The medium dependence of the clusters of mass 2 to 4 is included in a thermodynamical Green function approach and transitions between clusterized and unclusterized phases are discussed. Heavier clusters become important at higher densities and form the transition to homogeneous matter at high density. These are not yet fully included in the approach, limiting its applicability at higher densities. The model is formulated in the generalized relativistic mean field (RMF) approach. Light clusters are treated as independent degrees of freedom with a medium dependent self energy which gives rise to the coupling to the nucleon and meson degrees of freedom. Since nuclear matter is discussed for various asymmetries we also extract the symmetry energy, which is considerably modified at low density due to appearance of correlations. The EoS constructed should be of relevance to a wide range of problems, in particular to supernovae simulations. We also compare to other theoretical approaches used in this field. (author)