Physics of Atomic Nuclei最新文献

The article examines the possibilities of using neutral particle diagnostics to measure ion temperature and the isotopic composition of deuterium–hydrogen plasma in the Tokamak with Reactor Technologies (TRT). To determine the most favorable mutual arrangement of the diagnostic equipment, computer modeling of deuterium and hydrogen atomic fluxes was performed for the “active” diagnostic variant (with injection of a diagnostic atomic beam into the plasma) and the “passive” variant (without injection of a beam). As an example, the baseline operating regime with a plasma deuterium-to-hydrogen density ratio of 90% (D)/10% (H) is considered. It is shown that, in the “active” variant, the diagnostics allows local measurements of ion temperature and the plasma isotopic ratio with a spatial resolution of ≈13 cm. In the “passive” variant, this value is ≈30 cm. The temporal resolution is no worse than 10 ms for the “passive” variant and 1 ms for the “active” variant.

Future fusion reactors will require highly efficient methods for maintaining and heating the plasma. One of the most promising methods for solving this problem is the use of atomic sources with an energy level of about 1 MeV. Currently, it is impossible to obtain a high neutral yield efficiency for negative ion sources using gas charge exchange targets. An alternative method for neutralization is to use the effect of photodetachment of an excess electron from the ion. The idea of this method is based on the accumulation of high-power laser radiation in a mirror trap. The effectiveness of this approach directly depends on the amount of accumulated energy in the system of dielectric mirrors with a high reflectivity of more than 0.9999. Owing to the location of the mirrors close to the flow of high-energy charged particles, it is necessary to study the dependence of the degradation of the reflectance on bombardment by these particles. This paper examines two models of mirrors coated with the most popular materials TiO₂–SiO₂ and ZrO₂–SiO₂. A mirror model with a protective finishing layer based on the above materials is also proposed. As estimates show, the most resistant is a mirror coated with zirconium oxide and silicon oxide. The expected damage level at a fluence of 10¹³ cm^‒2 should not exceed the critical value of 6.1 × 10¹³ cm^‒2, as for the modified mirror.

Deuteron photodisintegration is calculated in the photon energy range (500{-}600) MeV, adopting a standard theory in which the nucleonic one-body current, meson exchange currents and isobar excitations are taken into account. The final-state interaction in the isospin-1 states is treated within a three-body (pi NN) model approach. The main attention is paid to the possible contribution of the (d^{*}(2380)) dibaryon. Its influence on this reaction is compared with its role in coherent (pi^{0}pi^{0}) photoproduction on a deuteron at the same energies.

The paper presents the results of measuring the distribution of ionization losses along the track of a recoil nucleus (({}^{210})Pb) with an initial energy of 146.5 keV from the decay of ({}^{214})Po. The measurements were carried out using a multi-cell matrix ((3times 3)) end-cap proportional counter (MCPC). Each cell is an end-face proportional counter (d=5) mm with a ring anode (d=0.7) mm. The MTPC was filled with a mixture of (96.3%textrm{Ar}+3.7%textrm{Xe}) at a pressure of 62 Torr. Recoil nuclei were emitted from the source surface in the central part of the drift electrode. The sour electric field of daughter products of ({}^{222})Rn decay from an auxiliary xenon carrier gas. Calibration was carried out using the energy releases of (alpha)-particles from the same source at a distance between the drift electrode and the recording plane. It was determined that the amplitude of pulses from recoil nuclei at the peak of the spectrum corresponds to an energy of (63.1pm 2.9) keV.

The results of pulsed measurements of the current–voltage characteristics of tapes based on high temperature superconductors are presented. A model was developed that describes the features of their formation at liquid nitrogen temperature. It is shown that, at currents significantly exceeding the critical current, stable states arise that possess a pronounced hysteretic character. The analysis carried out makes it possible to predict the behavior of the superconductor under operation at alternating current. The results discussed should be taken into account when designing large-scale superconducting magnetic systems, such as magnet coils for controlled thermonuclear fusion, which are subject to intense electromagnetic disturbances.

The results of an experiment and calculations aimed at studying the transmission of monochromatic neutrons by a lead single crystal are presented. The temperature dependence of the total cross-section obtained in the experiment is well described by a calculation taking one-, two- and three-phonon neutron scattering into consideration. An additional temperature-independent component of the total neutron interaction cross-section has been found. It is assumed that this component is associated with the presence of a small number of impurity atoms, which strongly absorb neutrons, in the studied lead sample. It is shown that in the absence of a neutron-absorbing impurity in lead, a lead single crystal can be used as a gamma-radiation filter without a significant neutron loss.

In accordance with the current requirements of Russian and foreign regulatory authorities, the modeling of beyond design basis accidents must be accompanied by a sensitivity analysis of the results of calculation. The outcome of the sensitivity analysis is the determination of the degree of influence of each uncertainty on the parameters under investigation. Within the scope of the performed work, an approach to performing sensitivity analysis using the SUSA program and the TRAP-KS software package was proposed, demonstrated by the example of beyond design basis accidents such as “trip of different number of reactor coolant pump sets with common-cause failure of programmable automatics systems,” “loss of vacuum in the condenser or other cases leading to turbine trip with common-cause failure of programmable automatics systems,” and “loss of nonemergency a.c. power to the station auxiliaries (loss of NPP power supply) with common-cause failure of programmable automatics systems.” These scenarios were selected on the basis of the condition of achieving maximum values of acceptance criteria: maximum cladding temperature, maximum pressure in the primary and secondary circuits, respectively. The results of the sensitivity analysis presented in this work include values characterizing the spread of the criterion parameters (maximum cladding temperature, maximum pressure in the primary and secondary circuits), Spearman rank correlation coefficients, and probability density function graphs and distribution charts of the results of calculation. The approach discussed in this paper allows for compliance with the current requirements of international and Russian supervisory bodies and can later be extended to all NPP projects with VVER reactor units. Additionally, this approach may be further applied to beyond design basis accidents involving failures of the accident protection system (ATWS) and failures of the industrial circuit due to a common cause.

In the paper, a methodological approach to the calculation of neutronic characteristics during the burnup of a block-type HTGR core using the MCU-HTR code based on the Monte Carlo method has been presented. A description of the developed full-scale three-dimensional model of the core and the approximations used and also some calculated results have been provided to demonstrate the capability of MCU-HTR to process and visually represent the output data.

ENDA-INR is a sea level prototype of the running now at high altitude in China ENDA (Electron-Neutron Detector array), being a part of the LHAASO experiment. The main task of the ENDA is measuring of primary cosmic ray energy spectrum using hadronic EAS component. The latter is a principal point because only hadrons form the EAS ‘‘skeleton’’ which defined all its properties at observation level. Preliminary experimental results obtained after 3.7 years of measurements are presented and analyzed.

In case of diboson production in (pp) collisions there is a non-negligible probability that some events passing the final selection in data are actually from different overlapping hard-scatter processes occurring within the same bunch-crossing. Such events, that consist of combination of two processes associated with different primary vertices, correspond to so-called pile-up background. Its contribution should be considered in analysis of diboson production at collider experiments. This article discusses an overlay Monte Carlo approach to obtain a theoretical prediction of the pile-up event count. According to the resulting estimate of the proposed method the impact of the pile-up background can be either subtracted from the data in the region of interest or accounted as an additional systematic uncertainty for the final result.