arXiv subjects

Oleksandr Gorbachenko

Publications and source records attributed to Oleksandr Gorbachenko.

9 recordsLinked to original sources

arXiv2020

Matter-wave interference originates mass-angle correlation in fusion-fission

Mass-angle correlation of fission fragments has been understood as manifestation of quasifission. We show that this is not so: the effect can originate from correlation between fusion-fission amplitudes with different total spins signifying matter-wave interference in compound nucleus processes. This resolves the well-known puzzle with the mass-angle correlation in the complete fusion sub-barrier reaction $^{16}$O+$^{238}$U. Our finding is important for more reliable predictions of production cross sections for superheavy elements. Matter-wave interference also produces quantum-classical transition to the time-orientation localization of the coherently rotating dinucleus in quasifission.

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arXiv2019

Comparison of Practical Expressions for E1 Photon Strength Functions

The closed-form expressions for the photon strength functions (PSF) are tested using the gamma-decay data of OSLO group. The theoretical calculations are performed for the Lorentzian models of PSF for electric and magnetic dipole gamma-rays. The criteria of minimum of least-square value as well as the root-mean-square deviation factor are used. It is shown that a rather good agreement is obtained within the Simple Modified Lorentzian model for E1 PSF modelling.

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arXiv2019

Description of nuclear photoexcitation by Lorentzian expressions for electric dipole photon strength function

The description of photoabsorption cross-sections of cold nuclei by closed-form Lorentzian models of photon strength functions for photoexcitation by electric dipole gamma-rays is considered. Systematics of the GDR parameters are given and input parameters of different analytical models are discussed The experimental data are compared with theoretical calculations for even-even nuclei using criteria of minimum of both least-square value and root-mean-square deviation factor. Simple extensions of the models with energy-dependent widths to high gamma-ray energies $\gtrsim $ 30MeV which hold the energy-weighted sum rule for E1 gamma-transitions in good approximation are proposed and tested.

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arXiv2019

Effect of compound nucleus spin correlations on fission fragment angular distribution

We extend a conventional description of the fusion-fission fragment angular distributions by introducing the correlation between compound nucleus states carrying different total angular momenta. This correlation results in the strong anisotropy and mass-angle correlation of fission fragments for compact saddle-point nuclear shapes for which the conventional description predicts almost isotropic angular distributions. The spin off-diagonal phase relaxation timescale, $\simeq 10^{-19}$ sec, obtained from analysis of anomalous fission fragment angular distributions in $^{12}$C+$^{236}$U, $^{16}$O+$^{232}$Th and $^{16}$O+$^{238}$U collisions at the sub-barrier energies is three orders of magnitude longer than the timescale of the compound nucleus thermalization. Expression for the angle-dependent time power spectrum for quasifission is also presented.

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arXiv2016

Improvements and Testing Practical Expressions for Photon Strength Functions of E1 Gamma-Transitions

Analytical expression for the E1 photon strength functions (PSF) is modified to account for the low-energy enhancement due to nuclear structure effects (presence of low-energy state (LES)). A closed-form expression of the E1 PSF function includes response of two nuclear states: LES and giant diplole resonance (GDR). Expression for the nuclear response function on electromagnetic field is based on a model of excitation of two coupled damped states. These approach is tested for different data sets for spherical nuclei. Impact on PSF shape of coupling between LES and GDR excitations is considered.

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arXiv2016

Effect of gamma-strength on nuclear reaction calculations

The results of the study of gamma-transition description in fast neutron capture and photofission are presented. Recent experimental data were used, namely, the spectrum of prompt gamma-rays in the energy range 2÷18 MeV from 14-MeV neutron capture in natural Ni and isomeric ratios in primary fragments of photofission of the isotopes of U, Np and Pu by bremsstrahlung with end-point energies $E_e$= 10.5, 12 and 18 MeV. The data are compared with the theoretical calculations performed within EMPIRE 3.2 and TALYS 1.6 codes. The mean value of angular momenta and their distributions were determined in the primary fragments $^{84}$Br, $^{97}$Nb, $^{90}$Rb, $^{131,133}$Te, $^{132}$Sb, $^{132,134}$I, $^{135}$Xe of photofissions. An impact of the characteristics of nuclear excited states on the calculation results is studied using different models for photon strength function and nuclear level density.

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arXiv2016

Gamma-rays from $^{nat}$Sn and $^{nat}$C induced by fast neutrons

The cross-sections of prompt gamma-ray production from $^{nat}$Sn and $^{nat}$C elements induced by 14.1-MeV neutrons were measured. The time-of-flight technique was used for n-gamma discrimination. The experimental results were compared with theoretical calculations performed by Empire 3.2 and Talys 1.6 codes using different models for photon strength function and nuclear level density.

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arXiv2013

Cross Sections of Neutron Reactions $(n,p)$, $(n, α)$, $(n, 2n)$ on Isotopes of Dysprosium, Erbium and Ytterbium at $\sim$ 14 MeV Neutron Energy

The cross sections of the nuclear reactions induced by neutrons at $E_n$= 14.6 MeV on the isotopes of Dy, Er, Yb with emission of neutrons, proton and alpha-particle are studied by the use of new experimental data and different theoretical approaches. New and improved experimental data are measured by the neutron-activation technique. The experimental and evaluated data from EXFOR, TENDL, ENDF libraries are compared with different systematics and calculations by codes of EMPIRE~3.0 and TALYS~1.2. Contribution of pre-equilibrium decay is discussed. Different systematics for estimations of the cross-sections of considered nuclear reactions are tested.

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arXiv2013

Nuclear Level Density within Extended Superfluid Model with Collective State Enhancement

For nuclear level densities, a modification of an enhanced generalized superfluid model with different collective state enhancement factors is studied. An effect of collective states on forming the temperature is taken into account. The ready-to-use tables for the asymptotic value of $a$-parameter of level density as well as for addition shift to excitation energy are prepared using the chi-square fit of the theoretical values of neutron resonance spacing and cumulative number of low-energy levels to experimental values. The systematics of these parameters as a function of mass number and neutron excess are obtained. The collective state effect on gamma-ray spectra and excitation functions of neutron-induced nuclear reactions is investigated by the use of EMPIRE 3.1 code with modified enhanced generalized superfluid model for nuclear level density.

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