arXiv subjects

V. A. Tarasov

Publications and source records attributed to V. A. Tarasov.

At least 19 recordsLinked to original sources

arXiv2023

Geant4 simulation of the moderating neutrons spectrum

In this paper we deal with the problem of predicting a steady-state neutron spectrum in media of arbitrary composition and geometry. The analytical calculations of such spectrum are often too complex, if at all possible. We describe a method of Geant4-based Monte Carlo calculation of the steady-state neutron spectrum in a medium containing a fixed neutron source. In addition to the steady-state spectrum, we obtain the snapshots of the neutron spectrum evolution in time, which may be thought of as the non-equilibrium neutron spectra, and their form is of considerable interest for further studies.

physics.comp-ph↗

arXiv2022

Production of the artificial 51Cr neutrino source in the BEST project

The production of the artificial 51Cr neutrino source with activity > 3 MCi for the experiment BEST is presented. This procedure consisted of making a 50Cr target and irradiating it with thermal neutrons in a nuclear reactor SM-3. The production of a target in the form of disks with a thickness of 4 mm and a diameter of 84 and 88 mm included enrichment (to 96.5% in 50Cr) of natural chromium in the form of oxyfluoride by gas centrifugation, electrolytic reduction and refining of metallic chromium, as well as the formation of chromium disks by spark plasma sintering. Simulations of various source geometries, neutron flux and nuclear transmutation were carried out to validate the design of the source, the irradiation device and the transport container, the required chemical purity of the target and the irradiation schedule in the reactor. The calculated activity of the source after 75 effective days of irradiation was 3.55 MCi. The activity of the source was measured by the calorimetric method and amounted to 3.41 MCi at the time of its delivery to the Baksan Neutrino Observatory. This is the most intense chemically pure neutrino source ever produced.

physics.ins-det↗

arXiv2022

A Search for Electron Neutrino Transitions to Sterile States in the BEST Experiment

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the $^{71}$Ge production rates within the two zones, as well as a possible rate difference between the zones. From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi $^{51}$Cr neutrino source 10 times for a total of 20 independent $^{71}$Ge extractions from the two Ga targets. The $^{71}$Ge production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with $^{71}$Ge doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured $^{71}$Ge production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the $4 σ$ deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best fit oscillation parameters of $Δm^2=3.3^{+\infty}_{-2.3}$ eV$^2$ and sin$^2 2θ=0.42^{+0.15}_{-0.17}$, consistent with $ν_e \rightarrow ν_s$ oscillations governed by a surprisingly large mixing angle.

nucl-ex↗

arXiv2022

Results from the Baksan Experiment on Sterile Transitions (BEST)

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos, $ν_{e}$, observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the \textit{gallium anomaly}, which could be interpreted as evidence for oscillations between $ν_e$ and sterile neutrino ($ν_s$) states. A 3.414-MCi \nuc{51}{Cr} $ν_e$ source was placed at the center of two nested Ga volumes and measurements were made of the production of \nuc{71}{Ge} through the charged current reaction, \nuc{71}{Ga}($ν_e$,e$^-$)\nuc{71}{Ge}, at two average distances. The measured production rates for the inner and the outer targets respectively are ($54.9^{+2.5}_{-2.4}(\mbox{stat})\pm1.4 (\mbox{syst})$) and ($55.6^{+2.7}_{-2.6}(\mbox{stat})\pm1.4 (\mbox{syst})$) atoms of \nuc{71}{Ge}/d. The ratio ($R$) of the measured rate of \nuc{71}{Ge} production at each distance to the expected rate from the known cross section and experimental efficiencies are $R_{in}=0.79\pm0.05$ and $R_{out}= 0.77\pm0.05$. The ratio of the outer to the inner result is 0.97$\pm$0.07, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20-24\% lower than expected, thus reaffirming the anomaly. These results are consistent with $ν_e \rightarrow ν_s$ oscillations with a relatively large $Δm^2$ ($>$0.5 eV$^2$) and mixing sin$^2 2θ$ ($\approx$0.4).

nucl-ex↗

arXiv2021

Measurement of neutrino source activity in the experiment BEST by calorimetric method

Experiments to study non-standard properties of neutrinos using high-intensity artificial neutrino sources require high accuracy in determining their activity. A calorimetric system to determine the activity of a 51Cr neutrino source in the experiment BEST with an accuracy better than 1% was created. The design of the calorimetric system and the main factors affecting the accuracy of measurements are considered. The results of measurements of the activity of the source made for the BEST experiment are presented. The value of the source activity from calorimetric measurements was 3.41 MCi at the beginning of the experiment.

hep-ex↗

arXiv2020

Neutron moderation spectrum considering inelastic scattering

For the first time an analytic expression was obtained for the inelastic neutron scattering law with an isotropic neutron source within the gas model, considering moderating medium temperature as a parameter. The inelastic scattering law is obtained, based on the solution of the kinematic problem of neutron inelastic scattering on a nucleus in laboratory coordinate system (L-system) in general case. I.e. in case not only a neutron but also a nucleus have arbitrary velocity vector in L-system. Analytic expressions are found for the neutron flux density and moderation spectrum in reactor fissile medium, both in case of the elastic scattering law, obtained earlier by the authors, and in case of the inelastic scattering law obtained in this paper. Both elastic and inelastic scattering laws are considered to be dependent on the medium temperature. The obtained expressions for neutron moderation spectra enable reinterpretation of physical nature of the processes that determine the shape of neutron spectrum in a wide energy range.

nucl-th↗

arXiv2020

Simulation of the traveling wave burning on epithermal neutrons on the year time scale

We present the newly obtained results of two computer simulations of the epithermal neutron-nuclear burning in natural uranium. Each of them modeled the period of six months of the traveling wave reactor (TWR) operation -- for two different flux densities of an external neutron source. The simulation results confirm the existence of a nuclear burning wave at longer time scales, and reveal the dependence of the wave burning modes on the parameters of an external neutron source.

nucl-th↗

arXiv2017

Impulse source of high energy neutrons emitted by fusion reactions after compression of D-T gas by cumulative detonation waves

We develop the physical model and the system of equations for the impulse neutron source (INS) of high-energy neutrons ($\sim$14 MeV) emitted by fusion reactions during compression of D-T gas by cumulative detonation waves. The system of INS equations includes a system of gas dynamic equations that takes into account the energy transfer by radiation, equations for the radiation flux, the equation of the shock adiabat (the Hugoniot adiabat) for a compressed gas, and the equation for the neutron yield. We perform the INS dynamics simulation for the spherical and cylindrical geometries, and calculate maximum temperatures of D-T plasma, its density and neutron yield in the pulse. The obtained temperature estimates and simulation results show that the thermonuclear fusion temperatures are reached within this approach, and the fusion reactions proceed. Their yield determines the yield of neutrons.

physics.plasm-ph↗

arXiv2017

Mechanical Analogy for the Wave of Nuclear Burning

We consider a model of neutron-nuclear wave burning. The wave of nuclear burning of the medium is initiated by an external neutron source and is the basis for the new generation reactors -- the so-called "traveling-wave reactors". We develop a model of nuclear wave burning, for which it is possible to draw an analogy with a mechanical dissipative system. Within the framework of the new model, we show that two burning modes are possible depending on the control parameters: a traveling autowave and a wave driven by an external neutron source. We find the autowave to be possible for certain neutron energies only, and the wave velocity has a continuous spectrum bounded below.

nucl-th↗

arXiv2016

Neutron Moderation Theory Taking into Accout the Thermal Motion of Moderating Medium Nuclei

In this paper we present the analytical expression for the neutron scattering law for an isotropic source of neutrons, obtained within the framework of the gas model with the temperature of the moderating medium as a parameter. The obtained scattering law is based on the solution of the kinematic problem of elastic scattering of neutrons on nuclei in the L-system in the general case. I.e. both the neutron and the nucleus possess the arbitrary velocity vectors in the L-system. For the new scattering law the flux densities and neutron moderation spectra depending on the temperature are obtained for the reactor fissile medium. The expressions for the moderating neutrons spectra allow reinterpreting the physical nature of the underlying processes in the thermal region.

nucl-th↗

arXiv2014

Ultraslow Wave Nuclear Burning of Uranium-Plutonium Fissile Medium on Epithermal Neutrons

For a fissile medium, originally consisting of uranium-238, the investigation of fulfillment of the wave burning criterion in a wide range of neutron energies is conducted for the first time, and a possibility of wave nuclear burning not only in the region of fast neutrons, but also for cold, epithermal and resonance ones is discovered for the first time. For the first time the results of the investigation of the Feoktistov criterion fulfillment for a fissile medium, originally consisting of uranium-238 dioxide with enrichments 4.38%, 2.00%, 1.00%, 0.71% and 0.50% with respect to uranium-235, in the region of neutron energies 0.015-10.0eV are presented. These results indicate a possibility of ultraslow wave neutron-nuclear burning mode realization in the uranium-plutonium media, originally (before the wave initiation by external neutron source) having enrichments with respect to uranium-235, corresponding to the subcritical state, in the regions of cold, thermal, epithermal and resonance neutrons. In order to validate the conclusions, based on the slow wave neutron-nuclear burning criterion fulfillment depending on the neutron energy, the numerical modeling of ultraslow wave neutron-nuclear burning of a natural uranium in the epithermal region of neutron energies (0.1-7.0eV) was conducted for the first time. The presented simulated results indicate the realization of the ultraslow wave neutron-nuclear burning of the natural uranium for the epithermal neutrons.

nucl-th↗

arXiv2013

On some fundamental peculiarities of the traveling wave reactor

On the basis of the condition for nuclear burning wave existence in the neutron-multiplicating media (U-Pu and Th-U cycles) we show the possibility of surmounting the so-called dpa-parameter problem, and suggest an algorithm of the optimal nuclear burning wave mode adjustment, which is supposed to yield the wave parameters (fluence/neutron flux, width and speed of nuclear burning wave) that satisfy the dpa-condition associated with the tolerable level of the reactor materials radioactive stability, in particular that of the cladding materials. It is shown for the first time that the capture and fission cross-sections of $^{238}$U and $^{239}$Pu increase with temperature within 1000-3000K range, which under certain conditions may lead to a global loss of the nuclear burning wave stability. Some variants of the possible stability loss due to the so-called blow-up modes (anomalous nuclear fuel temperature and neutron flow evolution) are discussed and are found to possibly become a reason for a trivial violation of the traveling wave reactor internal safety.

nucl-th↗

arXiv2013

Axion mechanism of Sun luminosity, dark matter and extragalactic background light

We show the existence of the strong inverse correlation between the temporal variations of the toroidal component of the magnetic field in the solar tachocline (the bottom of the convective zone) and the Earth magnetic field (the Y-component). The possibility that the hypothetical solar axions, which can transform into photons in external electric or magnetic fields (the inverse Primakoff effect), can be the instrument by which the magnetic field of the Sun convective zone modulates the magnetic field of the Earth is considered. We propose the axion mechanism of Sun luminosity and "solar dynamo -- geodynamo" connection, where the energy of one of the solar axion flux components emitted in M1 transition in 57Fe nuclei is modulated at first by the magnetic field of the solar tachocline zone (due to the inverse coherent Primakoff effect) and after that is resonantly absorbed in the core of the Earth, thereby playing the role of the energy modulator of the Earth magnetic field. Within the framework of this mechanism estimations of the strength of the axion coupling to a photon (g_{a γ} = 7.07e-11 1/GeV), the axion-nucleon coupling (g_{an} = 3.20e-7), the axion-electron coupling (g_{ae} = 5.28e-11) and the axion mass (m_a = 17eV) have been obtained. It is also shown that the claimed axion parameters do not contradict to any known experimental and theoretical model-independent limitations. We consider the effect of dark matter in the form of 17eV axions on the extragalactic back-ground light (EBL) and find that the theoretical spectral intensity of the EBL from decaying axions as a function of the observed wavelength is in good agreement with the known experimental data for the near ultraviolet, optical and near infrared bands (1500-20000 angstrom).

astro-ph.SR↗

arXiv2013

Fukushima plutonium effect and blow-up regimes in neutron-multiplying media

It is shown that the capture and fission cross-sections of 238U and 239Pu increase with temperature within 1000-3000 K range, in contrast to those of 235U, that under certain conditions may lead to the so-called blow-up modes, stimulating the anomalous neutron flux and nuclear fuel temperature growth. Some features of the blow-up regimes in neutron-multiplying media are discussed.

nucl-th↗

arXiv2012

The resonance absorption probability function for neutron and multiplicative integral

The analytical approximations for the moderating neutrons flux density like Fermi spectra, widely used in reactor physics, involve the probability function for moderating neutron to avoid the resonant absorption obtained using some restrictive assumptions regarding the acceptable resonances width. By means of multiplicative integral (Volterra integral) theory for a commutative algebra an analytical expression for the probability function is obtained rigorously without any restrictive assumptions.

nucl-th↗

arXiv2012

Comment on "Observation of electron-antineutrino disappearance at Daya Bay"

In recent Letter by An et al. [arXiv:1203.1669] Daya Bay measurements of non-zero value for the neutrino mixing angle θ_{13} with a significance of 5.2 standard deviations were reported. The value of sin^2 θ_{13} was determined with a χ^2 constructed with pull terms accounting for the correlation of the systematic errors. We show that a direct applying of the KamLAND parameters of mixing to Daya Bay-experiment under nonequilibrium geoneutrino spectrum of the nuclear burning process within the framework of nonzero nuclear georeactor χ^2 -hypothesis will produce a high uncertainty level and, as a result, a substantial distortion of the actual value of the neutrino mixing angle θ_{13}.

hep-ph↗

arXiv2012

Superluminal neutrinos and quantum cross-correlation theory of neutrino source location

Based on the developed cross-correlation theory for remote location of neutrino source with two-detector setup for neutrino detection the modification of arrangement of the OPERA experiment is suggested. Within the framework of computing experiment based on the OPERA experimental data we show that the use of this theory makes it possible not only to determine with high accuracy the delay time between neutrino signals but to eliminate the errors of blind analysis by which all necessary time corrections for determination of signal "technologically unremovable" delay time between CERN and GSL are performed.

physics.data-an↗

arXiv2011

KamLAND-experiment and Soliton-like Nuclear Georeactor. Part 1. Comparison of Theory with Experiment

We give an alternative description of the data produced in the KamLAND experiment, assuming the existence of a natural nuclear reactor on the boundary of the liquid and solid phases of the Earth's core. Analyzing the uncertainty of antineutrino spectrum of georeactor origin, we show that the theoretical (which takes into account the soliton-like nuclear georeactor) total reactor antineutrino spectra describe with good accuracy the experimental KamLAND-data over the years of 2002-2007 and 2002-2009, respectively. At the same time the parameters of mixing (Δ(m21)^2=2.5\cdot 10^-5 eV^2, tan^2θ12=0.437) calculated within the framework of georeactor hypothesis substantially differ from the parameters of mixing (Δ(m21)^2=7.49\cdot 10^-5 eV^2, tan^2θ12=0.436) obtained in KamLAND-experiment for total exposure over the period of 2002-2009. By traingulation of KamLAND and Borexino data we have constructed the coordinate location of soliton-like nuclear georeactors on the boundary of the liquid and solid phases of the Earth core. Based on the necessary condition of full synchronization of geological (magnetic) time scale and time evolution of heat power of nuclear georeactor, which plays the role of energy source of the Earth magnetic field, and also the strong negative correlation between magnetic field of the solar tachocline zone and magnetic field of the Earth liquid core (Y-component) we have obtain the estimation of nuclear georeactor average heat power ~30 TW over the years 2002-2009.

astro-ph.EP↗