Papers by Alexander Avdeenkov
Journal of Physics: Conference Series, 2020
We analyse an engineering model for a self-consistent calculation of the growth of an oxide film ... more We analyse an engineering model for a self-consistent calculation of the growth of an oxide film in circulation circuits with a heavy liquid metal coolant and concentrations of impurities (oxygen, iron, magnetite) from the point of view of possible uncertainty in determining the activity of oxygen. The modelling of thermohydraulic and physicochemical processes is based on solving the associated three-dimensional equations of hydrodynamics, convective-diffusive transport, and the formation of chemically interacting impurity components in the coolant volume and on the surface of steels. Model calculations of the influence of the uncertainty of oxygen activity on the rate and integral yield of iron, which under the given conditions of the oxygen regime after interaction with oxygen determines the appearance of magnetite. It is numerically demonstrated that in the saturation mode there is a model-independent characteristic, which is determined by the parabolic constant and thickness of ...
International Journal of Hydrogen Energy, 2018
ScienceDirect j o urn al h om epa ge: www.elsev ier.com/locate/he i n t e r n a t i o n a l j o u... more ScienceDirect j o urn al h om epa ge: www.elsev ier.com/locate/he i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 3 (2 0 1 8) 2 3 5 2 3 e2 3 5 3 7
Physics of Atomic Nuclei, 2010
Inclusion of the coupling of quasiparticle degrees of freedom with phonon degrees is a natural ex... more Inclusion of the coupling of quasiparticle degrees of freedom with phonon degrees is a natural extention of the standard QRPA approach. The paper presents the quantitative impact of this phonon coupling on the dipole strength and radiative neutron capture for the stable 124Sn and very exotic 150Sn isotopes, as an illustration, using the self-consistent version of the Extended Theory of Finite Fermi Systems. It was found that the phonon contribution to the pygmy-dipole resonance and radiative neutron capture cross section is increased with the (N − Z) difference growth. The results show that the self-consistent nuclear structure calculations are important for unstable nuclei, where phenomenological approaches do not work.
Physical Review C, 2011
The E1 strength function for 15 stable and unstable Sn even-even isotopes from A = 100 till A = 1... more The E1 strength function for 15 stable and unstable Sn even-even isotopes from A = 100 till A = 176 are calculated using the self-consistent microscopic theory which, in addition to the standard (Q)RPA approach, takes into account the single-particle continuum and the phonon coupling. Our analysis shows two distinct regions for which the integral characteristics of both the giant and pygmy resonances behave rather differently. For neutron-rich nuclei, starting from 132 Sn, we obtain a giant E1 resonance which significantly deviates from the widely-used systematics extrapolated from experimental data in the valley of β-stability. We show that the inclusion of the phonon coupling is necessary for a proper description of the low-energy pygmy resonances and the corresponding transition densities for A<132 nuclei, while in the A > 132 region the influence of the phonon coupling is significantly smaller. The radiative neutron capture cross sections leading to the stable 124 Sn and unstable 132 Sn, 150 Sn nuclei are calculated with both the (Q)RPA and the beyond-(Q)RPA strength functions and shown to be sensitive to both the predicted low-lying strength and the phonon coupling contribution. The comparison with the widely-used phenomenological Generalized Lorentzian approach shows considerable differences both for the strength function and the radiative neutron capture cross section. In particular, for the neutron-rich 150 Sn, the reaction cross section is found to be increased by a factor larger than 20. We conclude that the present approach may provide a complete and coherent description of the γ-ray strength function for astrophysics applications. In particular, such calculations are highly recommended for a reliable estimate of the electromagnetic properties of exotic nuclei.
Physical Review C, 2009
We have calculated the strength distributions of the giant monopole resonance in the even-A tin i... more We have calculated the strength distributions of the giant monopole resonance in the even-A tin isotopes (A = 112 − 124) which were recently measured in inelastic α-scattering. The calculations were performed within two microscopic models: the quasiparticle random phase approximation (QRPA) and the quasiparticle time blocking approximation which is an extension of the QRPA including quasiparticle-phonon coupling. We used a self-consistent calculational scheme based on the HF+BCS approximation. The single-particle continuum was exactly included on the RPA level. The self-consistent mean field and the effective interaction were derived from the Skyrme energy functional. In the calculations, two Skyrme force parametrizations were used. The T5 parametrization with comparatively low value of the incompressibility of infinite nuclear matter (K ∞ = 202 MeV) gives theoretical results in good agreement with the experimental data including the resonance widths.
Physical Review A, 2005
Recent experiments have observed condensation behavior in a strongly interacting system of fermio... more Recent experiments have observed condensation behavior in a strongly interacting system of fermionic atoms. We interpret these observations in terms of a mean-field version of resonance superfluidity theory. We find that the objects condensed are not bosonic molecules composed of bound fermion pairs, but are rather spatially correlated Cooper pairs whose coherence length is comparable to the mean spacing between atoms. We propose experiments that will help to further probe these novel pairs.
Modern Physics Letters A, 1996
A method taking account of a deviation of state occupation numbers from the thermal RPA prescript... more A method taking account of a deviation of state occupation numbers from the thermal RPA prescriptions is elaborated to study collective excitations in hot nuclei. This thermal renormalized random phase approximation (TRRPA) is from Ken-Ji Hara and D.J. Rowe. In developing the TRRPA, a formalism of the thermofield dynamics (TFD) is used. Some numerical results are given for the SU(2) model.
Journal of the Korean Physical Society, 2011
The E1 strength functions and radiative capture cross sections for several compound Sn isotopes, ... more The E1 strength functions and radiative capture cross sections for several compound Sn isotopes, including unstable 132 Sn and 150 Sn, have been calculated using the self-consistent microscopic theory. In addition to the standard RPA or QRPA approaches, the method includes the quasiparticlephonon coupling and the single-particle continuum. The results obtained show that the phonon contribution significantly affects the pygmy dipole resonance, which is of particular relevance for a proper description of the radiative neutron capture. The impact of the phonon coupling on the pygmy dipole resonance and the radiative neutron capture cross sections increases with the (N − Z) difference. For example, in the (0-10) MeV interval the full theory gives 17% of the energyweighted sum rule for 150 Sn and 2.8% for 124 Sn, whereas the continuum QRPA approach gives 5.1% and 1.7%, respectively. These results indicate the importance the self-consistent calculation can have, especially when applied to neutron-rich nuclei of astrophysical interest. The comparison with the widely-used phenomenological Generalized Lorentzian approach shows that the (Q)RPA approach gives an increase in the neutron capture cross section by a factor of 2 for 132 Sn and a factor of 10 for 150 Sn and that the inclusion of the phonon coupling still increases these cross sections even furhter, by a factor of 2-3.
The European Physical Journal D, 2006
The collisions between linear polar molecules, trapped in a microwave field with circular polariz... more The collisions between linear polar molecules, trapped in a microwave field with circular polarization, are theoretically analyzed. We demonstrate that the collisional dynamics is mostly controlled by two ratios ν/B and x = µ0E0/ B (ν is the microwave frequency, B is the molecular rotational constant, µ0 is the dipole moment, and E0 is the electric field amplitude). We discuss the dependence of collision cross sections on these ratios in order to find an advantageous condition for evaporative cooling.
Physical Review A, 2005
We discuss consequences of Fermi exchange symmetry on collisions of polar molecules at low temper... more We discuss consequences of Fermi exchange symmetry on collisions of polar molecules at low temperatures (below 1 K), considering the OD radical as a prototype. At low fields and low temperatures, Fermi statistics can stabilize a gas of OD molecules against state-changing collisions. We find, however, that this stability does not extend to temperatures high enough to assist with evaporative cooling. In addition, we establish that a novel "field-linked" resonance state of OD dimers exists, in analogy with the similar states predicted for bosonic OH.
Physical Review A, 2006
Collisions of polar 1 Σ state molecules at ultralow energies are considered, within a model that ... more Collisions of polar 1 Σ state molecules at ultralow energies are considered, within a model that accounts for long-range dipole-dipole interactions, plus rotation of the molecules. We predict a substantial suppression of dipole-driven inelastic collisions at high values of the applied electric field, namely, field values of several times B e /µ. Here B e is the rotational constant, and µ is the electric dipole moment of molecules. The sudden large drop in the inelastic cross section is attributed to the onset of degeneracy between molecular rotational levels, which dramatically alters the scattering Hamiltonian. As a result of the large ratio of elastic to inelastic collision rates, we predict that evaporative cooling may be feasible for 1 Σ state molecules in weak-field-seeking states, provided a large bias electric field is present.
Physics of Atomic Nuclei, 2016
A survey of some results in the modern microscopic theory of properties of nuclear reactions with... more A survey of some results in the modern microscopic theory of properties of nuclear reactions with gamma-rays is given. First of all, we discuss the impact of phonon coupling (PC) on the photon strength function (PSF) because it represents the most natural physical source of additional strength found for Sn isotopes in recent experiments that could not be explained within the standard HFB+QRPA approach. The self-consistent version of the Extended Theory of Finite Fermi Systems in the Quasiparticle Time Blocking Approximation, or simply QTBA, is applied. It uses the HFB mean field and includes both the QRPA and PC effects on the basis of the SLy4 Skyrme force. With our microscopic E1 PSFs, the following properties have been calculated for many stable and unstable even-even semi-magic Sn and Ni isotopes as well as for double-magic 132 Sn and 208 Pb using the reaction codes EMPIRE and TALYS with several nuclear level density (NLD) models: 1) the neutron capture cross sections, 2) the corresponding neutron capture gamma spectra, 3) the average radiative widths of neutron resonances. In all the properties considered, the PC contribution turned out to be significant, as compared with the standard QRPA one, and necessary to explain the available experimental data. The results with the phenomenological so-called generalized superfluid NLD model turned out to be worse, on the whole, than those obtained with the microscopic HFB+combinatorial NLD model. The very topical question about the M1 resonance contribution to PSFs is also discussed. Finally, we also discuss the modern microscopic NLD models based on the self-consistent HFB method and show their relevance to explain experimental data as compared with the phenomenological models. The use of these self-consistent microscopic approaches is of particular relevance for nuclear astrophysics, but also for the study of double-magic nuclei.
Bulletin of the Russian Academy of Sciences: Physics
ABSTRACT A self-consistent version of the model based on the method of Green’s functions which ta... more ABSTRACT A self-consistent version of the model based on the method of Green’s functions which takes into account conventional phonons of the random phase approximation, complex configurations like 2 quasiparticles⊗phonon ones, and exact single-particle continuum is used to describe many discrete natural-parity states and giant resonances in the 123Sn and 208Pb nuclei. The quasiparticle-phonon interaction is shown to be important not only for low-lying and high-lying collective states but also for low-lying noncollective states.
New Journal of Physics, 2015
We theoretically investigate trapped Bose condensates with strong dipolar interactions, in the pr... more We theoretically investigate trapped Bose condensates with strong dipolar interactions, in the presence of an external electrostatic field. As a prototype we consider polar OH molecules. Previously such systems have been studied in the case of a very strong external field that aligns all the dipoles along the field axis[1,2]. Here we relax this assumption and investigate the influence of
Physical Review C, 2013
ABSTRACT Ab initio quantum mechanical methods based on the Hartree-Fock approach are used to stud... more ABSTRACT Ab initio quantum mechanical methods based on the Hartree-Fock approach are used to study the probability of electron capture by the ^{7}Be nucleus in the ^{7}BeO crystal and the β phase of the ^{7}Be(OH)_{2} crystal modeled as clusters subjected to external pressure. Calculated rates of the increase of the ^{7}Be nuclear decay constant λ with pressure in these compounds are substantially smaller than the values found experimentally. We discuss possible reasons for discrepancy between the theory and the experiment. In particular, we demonstrate that the increase of λ in ^{7}BeO can be accounted for by the discussed phase transformation from the wurtzite to the rock-salt structure.
Physics Letters B, 2007
The Extended Theory of Finite Fermi Systems(ETFFS) describes nuclear excitations considering phon... more The Extended Theory of Finite Fermi Systems(ETFFS) describes nuclear excitations considering phonons and pairing degrees of freedom, using the effective Landau-Migdal interaction and nuclear mean fields obtained from experimental data. Here we employ the nuclear mean field derived from Skyrme interactions and the corresponding particle hole interaction. This allows to extend the range of applicability of the ETFFS to experimentally not yet investigated short-lived isotopes. We find that Skyrme interactions which reproduce at the mean field level both ground state properties and nuclear excitations are able to describe the spreading widths of the giant resonances in the new approach, but produce shifts of the centroid energies. A renormalization of the Skyrme interactions is required for approaches going beyond the mean field level.
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Papers by Alexander Avdeenkov