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Abramov B.D.,RAS Institute of Physics and Power Engineering
Journal of Physics: Conference Series | Year: 2017

It is shown in this paper that traditional formulas for reactivity effects calculation based on diffusion approximation small-perturbation theory sometimes need updating. The corresponding specifications are provided. These are caused by the unbalance of neutron "leakages" between subdomains (zones, cells, fuel subassemblies, etc.) of the reactor as a result of perturbation. The unbalance occurs because of the jumps of relative increments of diffusion coefficients on the subdomain interfaces. © Published under licence by IOP Publishing Ltd.


Gurbich A.F.,University of Surrey | Gurbich A.F.,RAS Institute of Physics and Power Engineering
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2014

The extension of the cross-section evaluation procedure to PIGE data was investigated and the first results are reported. Two different cases were studied: the gamma emission accompanying inelastic scattering of protons, and the (p,γ)-reaction. The corresponding theoretical calculations were performed in the framework of R-matrix and DWBA for the (p,p′γ) reaction on 23Na, and using statistical model for the proton radiative capture by 52Cr. The possibility of achieving a close fit to the experimental data is demonstrated. © 2014 Elsevier B.V. All rights reserved.


Avdeenkov A.V.,RAS Institute of Physics and Power Engineering | Avdeenkov A.V.,Stellenbosch University
New Journal of Physics | Year: 2015

We analyze the temporal evolution of the population of ultracold polar molecules in a microwave (mw) field with a circular polarization. The molecules are in their ground 1Σ state and treated as rigid rotors with a permanent dipole moment which interact with each other via the dipole?dipole (DD) interaction Vdd. The mw field mixes states with different quantum and photon numbers and the collisional dynamics in the mw field is mostly controlled by the ratios of the mw field frequency versus the rotational constant, and mw field Rabi frequency versus the rotational constant. There exists a special scattering process which is elastic by nature and due to a rotational energy exchange between the ground and the first excited rotational states. To analyze dynamics of polar molecules system in the mw field the equation of motion for the bare and dressed states is solved under different mw field parameters and molecular gas characteristics. Depending on the ratio of the Rabi frequency of a mw field and the magnitude of theDDinteraction, beatings and oscillations occur in the bare and dressed states time-development. At a certain relation between the magnitudes of the mw detuning δ and the DDinteraction δ = ± Vdd, peak structures appear in the population of the excited bare state. Each peak is associated with an avoided crossing between the dressed states adiabatic curves at the same position of mw detuning. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Litvinova E.,Helmholtz Center for Heavy Ion Research | Litvinova E.,Goethe University Frankfurt | Litvinova E.,RAS Institute of Physics and Power Engineering | Ring P.,TU Munich | Tselyaev V.,Saint Petersburg State University
Physical Review Letters | Year: 2010

A new class of many-body models, based on covariant density functional theory for excited states, is presented. It allows a parameter free description of the fragmentation of nuclear states induced by mode coupling of two-quasiparticle and two-phonon configurations. As compared to earlier methods it provides a consistent and parameter free theory of the fine structure of nuclear resonances. The method is applied very successfully to investigate the newly discovered low-lying dipole excitations in Sn and Ni isotopes with large neutron excess. © 2010 The American Physical Society.


Gurbich A.F.,RAS Institute of Physics and Power Engineering
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010

The evaluation of the cross-sections for any particular reaction consists in the elaboration of the most accurate possible cross-sections through incorporation of the all relevant experimental data in the framework of nuclear physics theory. The evaluated differential cross-sections for ion beam analysis are presented, comparison with the available experimental information is made, and discrepancies and other problems are discussed. The evaluated cross-sections can be retrieved for any scattering angle from the web site SigmaCalc (http://www.nds.iaea.org/sigmacalc/). They are also presented at the web site IBANDL (http://www.nds.iaea.org/ibandl) where a comparison of the available experimental data with results of the evaluation can be easily made. © 2010 Elsevier B.V. All rights reserved.


Svirin M.I.,RAS Institute of Physics and Power Engineering
Physics of Atomic Nuclei | Year: 2012

The cross section for the neutron-induced fission of 232Th target nuclei, σf (En), was described within statistical theory. The spectra of the mean multiplicity, v̄(En), and the mean energy, Ē(En), of secondary neutrons accompanying 232Th fission induced by neutrons of energy extending up to En = 20 MeV were analyzed on the basis of the chance structure of the cross section. © 2012 Pleiades Publishing, Ltd.


Trkov A.,International Atomic Energy Agency | Capote R.,International Atomic Energy Agency | Pronyaev V.G.,RAS Institute of Physics and Power Engineering
Nuclear Data Sheets | Year: 2015

Issues in evaluation methodology of the prompt fission neutron spectra (PFNS) and neutron multiplicity for the thermal-neutron-induced fission of the 235U are discussed. The inconsistency between the experimental differential and integral data is addressed. By using differential data as "shape data" good consistency was achieved between available sets of differential data. Integral dosimetry data have been used to define the PFNS slope at high outgoing neutron energies, where the quality of the differential data is poor. The inclusion into the fit of measured integral (spectrum-averaged) cross sections had a very small impact in the region where differential PFNS data are abundant and accurate, but removed the discrepancy with integral data at higher neutron emission energies. All experimental data are consistently fitted giving a PFNS average energy of 2.008 MeV. The impact on criticality prediction of the newly evaluated PFNS was tested. The highly enriched 235U solution assemblies with high leakage HEU-SOL-THERM-001 and HEU-SOL-THERM-009 benchmarks are the most sensitive to the PFNS. Criticality calculations for those solutions show a significant increase in reactivity if the average neutron energy of the fission neutrons is reduced from the ENDF/B-VI.5 value of 2.03 MeV. The proposed reduction of the PFNS average energy by 1.1% can be compensated by reducing the average number of neutrons per fission ν- at the thermal energy to the Gwin et al. measured value. The simple least-squares PFNS fit was confirmed by a more sophisticated combined fit of differential PFNS data for 233,235U, 239Pu and 252Cf nuclides with the generalised least-squares method using the GMA and GANDR codes. © 2014 Elsevier Inc.


Gai E.V.,RAS Institute of Physics and Power Engineering | Gurbich A.F.,RAS Institute of Physics and Power Engineering
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2013

A revision of the evaluated differential cross-section for elastic scattering of 4He from carbon was performed. The uncertainties to the evaluated data were assigned using an algorithm based on the covariance matrix of the experimental errors. © 2012 Elsevier B.V. All rights reserved.


Raskach K.F.,RAS Institute of Physics and Power Engineering
Nuclear Science and Engineering | Year: 2010

The differential operator method is an effective Monte Carlo technique developed for calculating derivatives and perturbations. It has often been applied to eigenvalue problems. This paper extends applicability of the method to inhomogeneous problems with internal and external neutron sources. Two issues associated with these problems were considered. First of all, it was necessary to use a special technique that treats inhomogeneous problems within the framework of the neutron generation method with a constant number of neutrons per generation. This technique optimizes Monte Carlo calculations and eliminates difficulties that appear in the classical technique as the effective multiplication factor approaches unity. Furthermore, use of the technique facilitated solving the usual issue of the differential operator method associated with fission source, or more exactly total neutron source, perturbations because some modification of the approach recently proposed for eigenvalue problems could be employed. The proposed technique can be used for calculating derivatives of reaction rates with respect to neutron cross sections or material densities. Perturbations of external source and geometrical parameters were outside the scope of this work.


Raskach K.F.,RAS Institute of Physics and Power Engineering
Nuclear Science and Engineering | Year: 2012

In this paper a new technique for accounting for multigroup cross section interdependence in sensitivity calculations is proposed and numerically investigated. In this technique the so-called implicit sensitivities representing multigroup cross-section interdependence are calculated through subgroup parameters. The technique turns out to be easy to implement in existing multigroup cross-section preparation codes and can cover both the homogeneous media and the heterogeneous media conventionally considered in such codes. This technique allows further extensions to cover arbitrary heterogeneous structures. The Monte Carlo technique of computing conventional sensitivities of k eff to multigroup cross sections used in this paper is also described.

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