Vol 81, No 9 (2018)

In dissociation in nuclear track emulsion of 4.5 and 1 A GeV/c¹²C nuclei, the formation of triplets of α particles in the Hoyle state (the second excited state 0⁺) is observed. This state is identified by the invariant mass, calculated from pair angles in the α triples in approximation of conservation of momentum per nucleon of the parent nucleus. An estimate of the contribution of the Hoyle state to the dissociation of ¹²C→ 3α is 10–15%.

It has been shown experimentally that, in a complex field of ionizing particles generated by cosmic rays, the highest values of the specific absorbed energy and, therefore, the density of charge formed during the ionization correspond to the locations of ion stopping. The modeling shows that, in the same locations, the ratio of the energy absorption by the nuclear continuum to the ionizing particle energy absorption by the electronic continuum of the medium linearly depends on the mass of the projectile.

This article presents experimental results on significant increase in the strength properties of the rapidly quenched ferritic/martensitic stainless steel obtained by consolidation of the rapidly quenched powder which was revealed during tension tests of the ring specimens of the nuclear fuel cladding tubes after exposure at 600°C in lithium with 0.05% hydrogen in comparison with exposure in pure lithium. The tension tests of the ring specimens of the nuclear fuel cladding tubes were carried out at room temperature. The microstructure and distribution of carbon, boron, carbide, and boride forming substitution alloying elements were investigated in detail after testing of rapidly quenched ferritic/martensitic stainless steel in pure lithium, lithium with 0.05% hydrogen and in argon environment. Significantly finer grains and formation of finely dispersed precipitates and pores in the ferritic/martensitic stainless steel after exposure in lithium with hydrogen addition are, obviously, the main reasons for the detected increase in the strength properties and decrease in plasticity.

In this paper, we have developed a model for calculating of the fission rate and burnup in an uranium- gadolinium fuel (UGF) pellet. The heterogeneous fission rate distribution at beginning of life of the uranium-gadolinium fuel is shown to lead to the formation of a radial gradient of the porosity in the UGF pellet and to the heterogeneous radiation-induced densification of the fuel. We have also developed physical models of thermophysical properties of He, ZrO₂, and zirconium cladding. Spatial and time temperature distributions in UGFE are calculated.

Problems relating to the high-accuracy computation of the Coulomb functions are considered and appropriate algorithms are described, including the representation by series, numerical integration of the Coulomb equation, and computation by means of recurrence relations.

The problem of noise filtering in observations of 2D functions of muon flux intensity distributions from the URAGAN hodoscope is considered. A filtering method based on the construction of sliding approximate local 2D models is proposed. A filtering algorithm based on sliding local piecewise linear 2D models is developed. The results of testing the algorithm on model and experimental observations for problems of Forbush decrease detection are presented. Errors of the algorithm are estimated on the basis of statistical modeling.

In this paper, we have developed a model of radiation-induced densification of uranium-gadolinium fuel. The fuel is established to be in the brittle state under irradiation in the volume of uranium-gadolinium fuel pellet containing a burnable neutron absorber and in the plastic state out of this volume. The plastic zone volume increases during burnup of the neutron absorber. The relative change in a pellet volume or length of a fuel rod for uranium-gadolinium fuel is shown to be lower than that for uranium oxide nuclear fuel having the same microstructure and irradiated under the same conditions (the neutron flux).

The design, procedure of assembling, and tests of drift tubes with the diameter of 30 and 15 mm made of mylar film 125 μm thick covered with aluminum from both sides are presented. The assembly technology of three-layer chambers of such tubes is described and some results showing the technical performance of the chambers are given.

The new coordinate-tracking detector based on drift chambers TREK, for research of ultrahighenergy cosmic rays is under development at National Research Nuclear University MEPhI. At the present, a prototype of the future detector—coordinate-tracking unit based on drift chambers (CTUDC)—is functioning. The prototype consists of 16 drift chambers. Results of experimental series have shown wide capabilities of this type of detectors for registration of muon bundles, including bundles with high density of particles. Results of operation of the prototype and prospects of developing a full-size detector TREK are presented.

Research on the use of photonuclear reactions in the production of isotopes for nuclear medicine is reviewed. The review includes the analysis of distinctive features of isotope production in electron accelerators and assessment of the possibility of such production. The review also presents the results of experimental studies on the production of short-lived ¹⁸F, ⁴⁷Sc, and ⁶⁷Cu radioisotopes with significantly high total activities in a split microtron with the electron energy of ~55MeV and the separation of ¹⁸F and ⁶⁷Cu with high specific activities from the targets.

The origin of cosmic rays is one of the most important questions in modern astrophysics. Leading world observatories are engaged in their search in our Galaxy and beyond. Current observations of bright sources of hard X-rays and gamma radiation require precise models of cosmic-ray accelerators and emission generation. Recent detection of astrophysical neutrinos with the energy exceeding 10¹⁵ eV achieved by the IceCube Neutrino Observatory and registration by the LOFAR observatory of the light cosmic-ray component at 10¹⁶–10¹⁷ eV have given rise to a wide discussion of whether its sources are galactic or extragalactic. H.E.S.S. observations of high-energy gamma-ray sources in compact massive clusters Westerlund 1 and Cl*1806-20 triggered a new search for the models of effective accelerators of high-energy cosmic rays, socalled galactic PeVatrons. In this paper, the properties of compact massive young stellar clusters as possible sources of cosmic rays, neutrinos, and gamma emission are discussed. We suppose that an expanding supernova remnant in a compact massive cluster is an effective cosmic-ray accelerator up to the energies of 10¹⁵ eV and beyond. Energy spectra of particles being accelerated in the system of colliding shocks generated by a supernova remnant interaction with nearby stellar winds have a broken power-law shape with a strong upturn around several teraelectronvolts and a cutoff energy at tens of petaelectronvolts. These sources provide the maximal emission flux at the maximal energies of the spectrum. Teraelectronvolt sources detected by H.E.S.S. could be related to supernova remnants in Westerlund 1 and Cl*1806-20 and be responsible for the 10% of the IceCube neutrino events. We have also shown that PeVatrons in the systems of colliding shocks can provide up to 80% of the light cosmic-ray component at the energies of 10¹⁶–10¹⁷ eV detected at the Earth.

Results of investigation of the high-energy cosmic-ray flux anisotropy using data on muon bundles are presented. The events were recorded in the period of 2013–2017 with the DECOR coordinate-tracking detector, which is a part of the unique scientific setup of the Experimental complex NEVOD. Methods for experimental data processing and taking atmospheric effects into account are described. Results of the analysis of two types of muon bundle events, which correspond to different ranges of primary particle energies (E > 10¹⁵ eV and E > 10¹⁶ eV) are discussed. Upper limits of the anisotropy amplitude for the two types of events are obtained.

The method of flicker-noise spectroscopy is used for remote identification of geoeffective disturbances of the solar wind. The method is based on the study of short-term variations in the cosmic-ray flux that arise when it crosses the perturbed regions in the inner heliosphere. The magnitude of the effect is usually small and it is hidden in statistical noise. The analysis uses data from a continuous flux of secondary atmospheric muons. Bumps of the “nonstationarity” parameter of time series of muons indicate the emergence of advanced signals (predictors) 1–3 days before the disturbances enter the Earth’s magnetosphere. Geoeffective events with a low threshold (A_p > 30 nT) for various types of solar wind are analyzed. The results are obtained using a ground-based muon hodoscope URAGAN (Moscow). The technique can be used for continuous monitoring of space weather.