arXiv subjects

V. M. Kolomietz

Publications and source records attributed to V. M. Kolomietz.

At least 19 recordsLinked to original sources

arXiv2021

Stochastic features of dissipative large-amplitude dynamics and nuclear fission

Within a density matrix approach for nuclear many--body system, it is derived non--Markovian Langevin equations of motion for nuclear collective parameters, where memory effects are defined by memory time. The developed stochastic approach is applied to study both the nuclear descent from fission barrier to a scission point and thermal diffusive overcoming of the barrier. The present paper is partly a review of our results obtained earlier and contains new results on the non--Markovian generalization of Kramers' theory of escape rate and on time features of the collective dynamics in the presence of periodic external modulation.

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arXiv2019

The effect of the Landau--Zener transitions on nuclear fission dynamics

In the paper, it is studied the influence of Landau-Zener transitions between nuclear many-body states on the dissipative properties of nuclear large--amplitude collective motion. Within the cranking-like approach, we describe the time evolution of a nuclear many-body system as the self-consistent motion in a space of intrinsic excitations and in a space of a single collective (deformation) parameter. By that we measure how the spectral statistics of the nuclear energy levels affects the fission rate at quite large initial temperatures of heavy nuclei.

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arXiv2015

Diffuse approximation to the kinetic theory in a Fermi system

We suggest the diffuse approach to the relaxation processes within the kinetic theory for the Wigner distribution function. The diffusion and drift coefficients are evaluated taking into consideration the interparticle collisions on the distorted Fermi surface. Using the finite range interaction, we show that the momentum dependence of the diffuse coefficient $D_{p}(p)$ has a maximum at Fermi momentum $p=p_{F}$ whereas the drift coefficient $K_{p}(p)$ is negative and reaches a minimum at $p\approx p_{F}$. For a cold Fermi system the diffusion coefficient takes the non-zero value which is caused by the relaxation on the distorted Fermi-surface at temperature $T=0$. The numerical solution of the diffusion equation was performed for the particle-hole excitation in a nucleus with $A=16$. The evaluated relaxation time $τ_{r}\approx 8.3\cdot 10^{-23}\mathrm{s}$ is close to the corresponding result in a nuclear Fermi-liquid obtained within the kinetic theory.

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arXiv2014

Symmetry energy: from nuclear matter to finite nuclei

We suggest a particular procedure of derivation of the beta-stability line and isotopic symmetry energy. The behavior of the symmetry energy coefficient $b(A,N-Z)$ is analyzed. We redefine the surface tension coefficient and the surface symmetry energy for an asymmetric nuclear Fermi-liquid drop with a finite diffuse layer. Following Gibbs-Tolman concept, we introduce the equimolar radius at which the surface tension is applied. The relation of the nuclear macroscopic characteristics like surface and symmetry energies, Tolman length, etc. to the bulk properties of nuclear matter is considered. The surface-to-volume symmetry energy ratio for several Skyrme-force parametrizations is obtained.

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arXiv2014

Diffusion on the Distorted Fermi Surface

The diffusion approximation to the relaxation on the distorted Fermi surface in a Fermi liquid is considered. The dependence of the relaxation time on the multipolarity of a Fermi surface deformation is established. The time evolution of the non-equilibrium particle-hole excitations is studied.

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arXiv2013

Gamma-radiation in non-Markovian Fermi systems

The gamma-quanta emission is considered within the framework of the non--Markovian kinetic theory. It is shown that the memory effects have a strong influence on the spectral distribution of gamma-quanta in the case of long-time relaxation regime. It is shown that the gamma-radiation can be used as a probe for both the time-reversible hindrance force and the dissipative friction caused by the memory integral.

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arXiv2013

Gibbs-Tolman approach to the curved interface effects in asymmetric nuclei

We redefine the surface tension coefficient and the symmetry energy for an asymmetric nuclear Fermi-liquid drop with a finite diffuse layer. Considering two-component charged Fermi-liquid drop and following Gibbs-Tolman concept, we introduce the equimolar radius $R_{e}$ of sharp surface droplet at which the surface tension is applied and the radius of tension surface $R_{s}$ (Laplace radius) which provides the minimum of the surface tension coefficient $σ$. We have shown that the nuclear Tolman length $ξ$ is negative and the modulus of $ξ$ growth quadratically with asymmetry parameter $X=(N-Z)/(N+Z)$.

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arXiv2012

Nucleon distribution in nuclei beyond β-stability line

The radii of nucleon distribution, bulk density, and neutron skin in nuclei beyond the β-stability line are studied within the direct variational method. We evaluate the partial equation of state of finite nuclei and demonstrate that the bulk density decreases beyond the beta stability line. We show that the growth of the neutron skin in unstable nuclei does not obey the saturation condition because of the polarization effect. The value of the neutron-skin thickness Δr_{np}=\sqrt{ }-\sqrt{ } is caused by the different radii (skin effect) and only slightly by the different shapes (halo effect) of neutron and proton distributions. The relative contribution of both effects depends on the competition between the symmetry energy, and the spin-orbit and Coulomb interactions. The calculations of the isovector shift of the nuclear radius Δr_{np} show its primarily linear dependence on the asymmetry parameter X=(N-Z)/A.

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arXiv2012

Curved and diffuse interface effects on the nuclear surface tension

We redefine the surface tension coefficient for a nuclear Fermi-liquid drop with a finite diffuse layer. Following Gibbs-Tolman concept, we introduce the equimolar radius R_e of sharp surface droplet at which the surface tension is applied and the radius of tension surface R_s which provides the minimum of the surface tension coefficient σ. This procedure allows us to derive both the surface tension and the corresponding curvature correction (Tolman length) correctly for the curved and diffuse interface. We point out that the curvature correction depends significantly on the finite diffuse interface. This fact is missed in traditional nuclear considerations of curvature correction to the surface tension. We show that Tolman's length ξis negative for nuclear Fermi-liquid drop. The value of the Tolman length is only slightly sensitive to the Skyrme force parametrization and equals ξ=-0.36 fm.

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arXiv2011

Non-Markovian diffusion over potential barrier in the presence of periodic time modulation

The diffusive non-Markovian motion over a single-well potential barrier in the presence of a weak sinusoidal time-modulation is studied. We found non-monotonic dependence of the mean escape time from the barrier on a frequency of the periodic modulation that is character to the stochastic resonance phenomenon. The resonant acceleration of diffusion over the barrier occurs at the frequency inversely proportional to the mean first-passage time for the motion in the absence of the time-modulation.

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arXiv2011

Giant neutron halo in nuclei beyond beta-stability line

The radii of nucleon distribution and neutron skin in nuclei beyond the β-stability line are studied within the extended Thomas-Fermi approximation. We show that the growth of neutron skin in unstable nuclei does not obey the saturation condition because of the neutron coat. The neutron coat indicates the possibility of giant neutron halo which is growing with moving away from the beta stability line. We demonstrate the presence of strong shell oscillations in the charge radius R_C and the relation of R_C to the isospin shift of neutron-proton chemical potentials Δλ=λ_n-λ_p for nuclei beyond the beta-stability line at fixed value of mass number A.

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arXiv2009

A new derivation of symmetry energy from nuclei beyond the β-stability line

We suggest the procedure of direct derivation of the symmetry energy from the shift of neutron-proton chemical potentials Δλ=λ_{n}- λ_{p} for nuclei beyond the beta-stability line. We observe the presence of anomalous strong (about 15%) shell oscillations at the symmetry energy coefficient b_{sym}. Our results do not confirm the existence of exceptionally large values of the symmetry energy coefficient at mass number A\approx 100 which was earlier reported in Ref.[2]. Using the fitting procedure, we have evaluated the volume, b_{sym,vol}, and surface, b_{sym,surf}, contributions to the symmetry energy. We have estimated the experimental value of surface-to-volume ratio as r_{S/V}=|b_{sym,surf}}|/b_{sym,vol}\approx 1.7 for the fitting interval A\geq 50.

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arXiv2009

A dependence of the enhancement factor in energy-weighted sums for isovector giant resonances

We consider the energy weighted sums (EWS) for isovector giant dipole resonances (IVGDR) in finite nuclei within Landau kinetic theory. The dependence of both IVGDR energy, $E_{IVGDR}$, and the EWS enhancement factor, $κ(A)$, on the mass number $A$ occurs because of the boundary condition on the moving nuclear surface. The values of $E_{IVGDR}A^{1/3}$ and $κ(A)$ increase with $A$. The obtained value of the enhancement factor is about 10% for light nuclei and reaches approximately 20% for heavy nuclei. A fit of the enhancement factor to the proper experimental data provides a value for the isovector Landau amplitude of $F'_1\simeq 1.1$.

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arXiv2009

Isovector response and energy-weighted sums in hot nuclei

We investigate the collective response function and the energy-weighted sums (EWS) $m_k$ for isovector mode in hot nuclei. The approach is based on the collisional kinetic theory and takes into consideration the temperature and the relaxation effects. We have evaluated the temperature dependence of the adiabatic, $E_1=\sqrt{m_1/m_{-1}}$, and scaling, $E_3=\sqrt{m_3/m_1}$, energy centroids of the isovector giant dipole resonances (IVGDR). The centroid energy $E_3$ is significantly influenced by the Fermi surface distortion effects and, in contrast to the isoscalar mode, shows much weaker variation with temperature. Taking into account a connection between the isovector sound mode and the corresponding surface vibrations we have established the $A$-dependence of the IVGDR centroid energy which is in a good agreement with experimental data. We have shown that the enhancement factor for the "model independent" sum $m_1$ is only slightly sensitive to the temperature change.

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arXiv2008

Non-Markovian large amplitude motion and nuclear fission

The general problem of dissipation in macroscopic large-amplitude collective motion and its relation to energy diffusion of intrinsic degrees of freedom of a nucleus is studied. By applying the cranking approach to the nuclear many body system, a set of coupled dynamical equations for the collective classical variables and the quantum mechanical occupancies of the intrinsic nuclear states is derived. Different dynamical regimes of the intrinsic nuclear motion and its consequences on time properties of collective dissipation are discussed. The approach is applied to the descant of the nucleus from the fission barrier.

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arXiv2008

Symmetry Energy for Nuclei Beyond the Stability Valley

We apply the direct variational method to derive the equation of state for finite nuclei within the stability valley. The extended Thomas-Fermi approximation for the energy functional with Skyrme forces is used. Using the leptodermous expansion for the profile nucleon densities, we have studied the neutron coat and the isospin symmetry energy for neutron-rich nuclei. Using equation of state for the pressure, we derive the region of spinodal instability of finite nuclei and its dependence on the mass number, the asymmetry parameter and the Skyrme force parameters. We suggest the procedure of derivation of the isospin symmetry energy from analysis of the isospin shift of chemical potential $Δλ= λ_n - λ_p$ beyond the beta-stability line.

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arXiv2008

Isovector energy-weighted sums for hot nuclei in presence of relaxation processes

We investigate the collective response function and the energy-weighted sums m_k for isovector mode in hot nuclei. The approach is based on the collisional kinetic theory and takes into consideration the temperature and the relaxation effects. Taking into account a connection between the isovector sound mode and the corresponding surface vibrations we have established the A-dependence of the enhancement factor for the isovector sum rule in a good agreement with experimental data. We have shown that the enhancement factor for the "model independent" sum m_1 is only slightly sensitive to the temperature change.

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arXiv2007

Collective motion in quantum diffusive environment

The general problem of dissipation in macroscopic large-amplitude collective motion and its relation to energy diffusion of intrinsic degrees of freedom of a nucleus is studied. By applying the cranking approach to the nuclear many-body system, a set of coupled dynamical equations for the collective classical variable and the quantum mechanical occupancies of the intrinsic nuclear states is derived. Different dynamical regimes of the intrinsic nuclear motion and its consequences on time properties of collective dissipation are discussed.

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