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A multichannel scintillation spectrometer with a thickness of 2.5X0 has been calibrated on a secondary electron beam with energies of 23−280 MeV at the Pakhra accelerator of the Lebedev Physical Institute. The relative energy resolution of the spectrometer is determined by the electron energy and the spectrometer thickness. The best relative energy resolution of the spectrometer is attained at an electron energy of ~90 MeV; its values are δ = 13 and 9.4% at spectrometer thicknesses of 1.0X0 and 2.5X0, respectively.

The physical aspects and main results of reactor tests of a two-stage core consisting of fresh fuel assemblies and a significant number of fuel assemblies from the previous core, which are left for re-burning on the KV-1 test facility in a 3+ run, are presented. In spite of the significant heterogeneity of the core and the complexity of its computational and experimental neutronics modeling, neutronics engineering codes made it possible to calculate the governing neutronics parameters with acceptable accuracy. The combination of re-burning and make-up fuel assemblies made it possible to test fuel assemblies with high power contrast, including in the natural circulation regime in a wide power range. The technical solutions implemented in the 3+ run made it possible to create a database for validating with minimal financial cost and test time the resource reliability of cores which are under construction and cores for future ship nuclear power facilities.

The results of measurements of the dependence of the full width at half-maximum and the relative intensity of spectral peaks of parametric X-ray radiation (PXR) for various crystallographic planes on the grain size of a micrometer diamond powder are presented.

The calibration results are presented for a scintillation hodoscopic spectrometer of charged particles, which has been designed for an experiment on the search for a heavy electron on the bremsstrahlung photon beam at the Pakhra accelerator of the LPI. The relative energy and coordinate resolutions of the spectrometer at electron energy E = 40 MeV are δ = 22% and σx = 9.5 mm, respectively. It has been determined that the width of electromagnetic showers in the transverse direction can be described by the energy dependences Δ ~ lnE at E 100 MeV.

In this paper, we report the characteristics of the generated beams, the extracted electron beam and the beam of secondary electrons/positrons, of the LPI accelerator complex Pakhra as of November 2019 for testing and calibrating detectors used in large accelerator and astrophysical experiments. At energies of 250–500 MeV of the electron beam ejected into Hall 1 from the S-25R synchrotron, its energy resolution is δ ~ 1% and the intensity can be changed by collimators in the range of 103–1010 s–1. The quasi-monochromatic beam of secondary electrons produced in Hall 2 typically has an energy in the range of 50–300 MeV, a corresponding energy resolution of δ = 14–2%, and an intensity of ~ 102 s–1. The performed simulation of the characteristics of the secondary positron beam allowed selecting the optimal geometry of the setup and showed good agreement with the experimental data obtained later.

Maps are plotted for the hot plastic deformation of titanium-based alloys with a high-temperature polymorphic transformation, namely, martensitic 23A, 5VA and PT3V alloys. Hot plastic compression is modeled using a DIL 805 A/D dilatometer. Samples in the form of ∅5 × 10 mm cylinders are compressed to a strain of 0.3 in the temperature range 600–1100°C at a strain rate from 10–3 to 10 s–1. The α ↔ β transformation temperatures are 800–900°C in alloy 23A, 880–900°C in 5VA, and 900–920°C in PT3V, and they fall into the temperature range of hot compression. The process maps show the effect of mechanical energy dissipation in changing the shape and structure of the samples. The dissipation of introduced mechanical energy is found to be due to the operation of the following two structural mechanisms: accommodative elastoplastic relaxation in ensembles of lattice defects with η ≈ 25% and the hcp ↔ bcc crystallographic transformation with an efficiency η ≈ 15%.

A complex of accessory W-bearing tantalo-niobates (columbite-(Fe), columbite-(Mn), tantalite-(Mn), microlite group minerals, and Ta-bearing rutile) involving “wolframoixiolite” has been found for the first time in Li–F granite and ongonite of the Arga–Ynnakh–Khaya Pluton in East Yakutia. The rocks that contain wolframoixiolite, as well as the composition and typical features of the mineral, are described: its high Fe concentration, the leading mineral-forming role of niobium, widely variable W and Ta contents, and paragenesis with W-bearing columbite-(Mn), Ta–Nb ferberite, lepidolite, and topaz. Wolframoixiolite from the Arga–Ynnakh–Khaya Pluton is formed by polymorphic transition of columbite-(Fe) at the late stage of Li–F granite crystallization. A review of accessory mineralization in rare-metal Li–F granites of Eurasia, taking the new finding into account, indicates that wolframoixiolite is a typical accessory phase in Li–F granites and may indicate rare-metal granite magmatism accompanied with tin–rare-metal mineralization.

—The problem of the origin of “white granite” in the Kester harpolith of the Arga–Ynnakh–Khaya Pluton is discussed. The morphology, occurrence, and nature of the intrusive contacts of the Kester harpolith prove its magmatic origin. The petrographic and petrochemical properties of “white granite” allow its identification as a postorogenic rare-metal high-phosphorus granite of the Li-F geochemical type. The magmatic genesis of the “white granite” texture is supported by statistical methods. The composition, typomorphic properties, ontogenetic features internal structure and relationship of accessory minerals indicate that the major accessories of the granite, that is, cassiterite, columbite, tantalite, “wolframoixiolite,” zircon, and ferberite, were formed at the late stage of the low-temperature rare-metal granitic melt. The Kester harpolith within the Arga–Ynnakh–Khaya granite pluton and the eponymous tin–rare-metal deposit genetically related to it are a part of the Far East Superprovince of rare-metal granites.

The characteristics of systems based on Cherenkov counters for monitoring the intensity of a bremsstrahlung photon beam at the S-25R Pakhra accelerator of the Lebedev Physical Institute are presented.

Characteristics of the calibration quasi-monochromatic secondary electron beam of the S-25R “Pakhra” accelerator of the Lebedev Physical Institute, based on the SP-57 magnet are presented. At the electron beam energy of 280 MeV, a collimator diameter in front of trigger counters of 3 mm, and a copper converter thickness of 1–3 mm, the relative energy resolution and beam intensity are δ = 2.2—4.4% and ~16—23 e–/s, respectively.

The phenomenon of an abnormally high concentration of tantalum (5.3–17.9% of Ta2O5) in accessory cassiterite from lithium–fluoric granites of the Arga-Ynnakh-Khaysky massif in East Yakutia is described. The significant isomorphic capacity of the cassiterite structure in relation to the tapiolite impurity, which reaches 15.1–39.8%, is established. It is concluded that the origin of tantalum-bearing cassiterite is determined by the specific crystallization conditions of lithium–fluoric granites, and their wide distribution in the Far East of Russia requires further study of the typochemistry of accessory cassiterite from rare-metal granites and genetically related metasomatites.

The pyrochlore-group minerals in ongonite and zwitter of the Verkhneurmiysky granite pluton in the Badzhal district, Russian Far East are reported. The composition, genesis, and crystallization sequence are characterized. Three rare species of pyrochlore, pyrochlore-I and pyrochlore-II in ongonite, and pyrochlore-III in zwitter are found for the first time in the Russian Far East. Pyrochlore-I is a possible new member of the pyrochlore group, bismuth-bearing “oxyferropyrochlore”; pyrochlore-II is an uranium-bearing and iron-bearing hydrokenopyrochlore; and pyrochlore-III is a lead-and iron-bearing hydrokenopyrochlore. All three pyrochlore species result from an alteration of early accessory minerals: niobium wolframite, samarskite, ishikawaite, wolframoixiolite, scheelite, and fergusonite. The Far East pyrochlore is characterized by extremely high Ta, W, and Fe contents. Compositional variations in pyrochlore are caused by substitution of Nb, Ta, W at the B site of the crystal structure and exchange of U, Pb, Bi, and Fe at the A site. The Ta, Bi, and Th concentrations decrease during transition from the late magmatic to greisen stage; the mineral forming significance of Nb, W, U, Y, Pb, and H2O increases as followed: Ta, Nb, Bi, Fe, Th, As, P, Ca, Ti → Nb, Ta, W, U, Fe, HREE, Sc, Mn, Na, H2O → Nb, Pb, W, Fe, Y, H2O.

The design of a fast relativistic electron beam monitor based on a Cherenkov counter capable of determining the intensity in the range of 106–1011 electron/s is described.

The results of calibration of the total-absorption Cherenkov spectrometer based on TF-1 lead glass of a thickness 14.8X0 using a quasi-monochromatic electron beam are presented. It is found that the energy resolution is 89–10% in the electron beam energy range E = 6–285 MeV, correspondingly.

The developmental history of the series-produced core for nuclear icebreakers and its conceptual and structural designs and the computational-methodological base of the physical design are presented. The fundamental differences from VVER-type power reactor cores, which are due to the specific operating conditions of ice breakers, are discussed. Measurements of the basic neutronic characteristics of a series-produced icebreaker core are presented and compared with calculations performed with the tested software system VKN-02. Experimental data confirm that the accuracy of the VKN-02 system in calculating the neutronic characteristics determining nuclear safety and the thermal engineering reliability of an icebreaker core is acceptable.

The characteristics of the quasi-monochromatic calibration beam of secondary electrons at the Pakhra accelerator (Lebedev Physical Institute) on the basis of the SP-57 magnet are presented. The energy resolution of the beam with a copper converter 0.1–5.0 mm thick and an interpolar magnet gap of 6 cm is δ = 10.0–4.5% in accordance with the energy in the electron-beam energy range E = 98–294 MeV.

The by-products of the Far East Sn deposits related to Li–F granites include trace elements. The petrography and mineral composition of the Sn-bearing metasomatites of the Verkhneurmiysky ore cluster (VUOC) of the Amur region (feldspatites, greisens, zwitters, turmalinites, and chloritites) and the multistage complex rare-metal (RM) mineralization of the Sn occurrences in area of Li–F granites are studied. The minerals of strategic metals (Nb, Ta, W, Y, REE (from La to Lu), Be, Li, Rb, Zr, Hf, In, Sc, Se, Cd, and Te) are found. The RMs occur as minerals (fergusonite, plumbopyrochlore, allanite, monazite, roquesite, sakuraiite, etc.) and isomorphic substitution in the ore (wolframite; cassiterrite; Cu, Sn, Fe, Mo, Zn, and Pb sulfides; native bismuth; etc.) and rock-forming (fluorite, siderophyllite, muscovite, and epidote) minerals. Some RMs (Y, REEs, Nb, In, and Sc) most frequently occur in Sn-bearing metasomatites. The RM minerals formed during the VUOC evolution (from the premineral feldspatite to the postmineral chloritite stage) with decreasing intensity of RM mineral formation and compositional evolution from lithophile to chalcophile RMs: (LREE, Zr, Hf) → (W, Nb, Ta, Y, HREEs, Sc) → (Sn, In, Cd, Se, Te). The formation of the VUOC RM mineralization was caused by magmatic, metasomatic, and crystal chemical factors. The possible complex exploration of the Far East Sn deposits is shown for areas of Li–F granites.

For the first time, lithium-fluoric granites and ongonites of the Arga-Ynnakh-Khaysky massif (East Yakutia) have been revealed to contain an accessory complex of tungsten-bearing tantalum-niobates ( columbite-(Fe), columbite-(Mn), tantalite-(Mn), minerals of microlite group, tantalic rutile ) including «wolframoixiolite». These rocks containing wolframoixiolite, their composition and typomorphic features are described: they are highly ferriferous, with major geochemical role of niobium and wide variations of tungsten and tantalum concentrations. Wolframoixiolite occurs there in paragenesis with tungsten-bearing columbite-(Mn), tantalum-niobium ferberite, lepidolite and topaz. Wolframoixiolite of the Arga-Ynnakh-Khaysky massif was formed on a late-magmatic stage of lithium-fluoric granites crystallization by polymorphic transformation of columbite-(Fe). The study of accessory mineralization in rare-metal granites of Eurasia allows, taking into account a new find, to draw a conclusion, that wolframoixiolite is typomorphic accessory mineral in lithium-fluoric granites and may be looked as the indicator of rare-metal-granite magmatism with accompanying tin-rare-metal ore mineralization.

The possibility of using the effect of full energy absorption in a light scintillator when an electron beam passes through it to determine the energy characteristics of a low and medium energy beam (the absorbed energy method) is experimentally presented. The energy calibration of the quasi-monochromatic electron beam of the Pakhra accelerator of the P. N. Lebedev Physical Institute of the Russian Academy of Sciences using scintillation detectors with a thickness of 14.5, 20, 23.5 and 51.2 cm was performed. For electron beam energies up to about 100 MeV and scintillation detector thicknesses from 5 to 20 cm the accuracy of electron beam energy determination was 10 to 20%, respectively., Comment: 11 pages, 10 figures, 5 references , scientific article

The results of calibration by cosmic muons of a shower lead-scintillation spectrometer of the sandwich type designed to work in high-intensity photon and electron beams with an energy of 0.1 - 1.0 GeV are presented. It was found that the relative energy resolution of the spectrometer depends on the angle of entry of cosmic muons into the spectrometer in the vertical plane and does not depend on the angle of entry in the horizontal plane. The relative energy resolution of the spectrometer was 16%. Placing an additional lead-scintillation assembly in front of the spectrometer improved the relative energy resolution of the spectrometer to 9%., Comment: 8 pages, 5 figures, 5 references

Niobium minerals in zwitter and lithium–fluorine granite of the Verkhneurmiysky granitic massif in the Amur River region—fergusonite-(Y), euxenite-(Y), samarskite-(Yb), aeschynite, Nb-bearing wolframite— have been described and the similarity of their species composition established. The same-named and crystal-chemically allied minerals from zwitter and granite are characterized by similar complexes of such trace elements as W, REE, Mn, Fe, Pb, U, and Sc. A genetic link between Sn-bearing zwitter and Li–F granite is stated. Compositional varieties of niobium minerals in granite and zwitter reflect a change in the physicochemical conditions of mineral formation, when the magmatic stage is followed by a pneumatolytic–hydrothermal process. The postmagmatic evolution of niobium minerals is characterized by increased concentrations of Y, Pb, U, Fe and decreased concentrations of W, Ta, REE, Ti, Sc, and Th. The mineral occurrences in the western sector of the Verkhneurmiysky Cu–W–Sn cluster are appraised as promising for Nb, Y, and REE. Fergusonite, samarskite, euxenite, and Nb-bearing wolframite are indicators of rare metal mineralization.

The paper reports the results of SIMS and SEM-EDS study of rock-forming minerals from melt pockets in the central part of a spinel peridotite xenolith taken from Quaternary alkaline basalts of Sverre Volcano in the northwestern part of West Spitsbergen Island. Olivine and clinopyroxene are analyzed to trace changes related to the metasomatic interaction between spinel lherzolite and a carbonate melt with formation of corresponding secondary minerals and silicate glass. It is established that the metasomatic interaction of the carbonate melt with minerals of host spinel lherzolite is accompanied by partial recrystallization of olivine and clinopyroxene, or crystallization of the second generation of these minerals. Percolating carbonate melt caused significant changes in the major, trace, and rare-earth element composition of the considered minerals, thus placing constraints on the use of the composition of these minerals for calculation of P–T parameters, estimating equilibrium, and modeling petrological processes in mantle.

Problems of the synthesis of ultrawideband fixed phase shifters with a new structure of the electric circuit of the phase-shifting channel formed by means of connection of two identical elements consisting of weakly coupled stepped transmission lines with stubs have been solved. The advantage of the proposed structure over the available structures is shown.

The results of experimental investigations of the spatial and energy distributions of the thermal and epithermal neutrons in a cassette fuel assembly, similar in design to that developed for the RITM-200 reactor core in the universal nuclear icebreaker, are presented. The measurements were performed using activation detectors with the isotopes 63Cu, 55Mn, and 197Au. It is shown that the structural nonuniformities of the fuel assembly (central water cavity, reactivity compensation system absorbing rod, strongly screened rods with consumable absorber) create significant thermal neutron flux nonuniformity over the cross-section of a fuel assembly. The flux distribution of epithermal neutrons with energy >0.4 eV is almost uniform. The experimental data are supported by calculations.

Accessory wolframite with an extraordinarily high rhenium content (2.93–3.52%) in ongonite from the Badzhal area in the Far East is described. The capacity of tungsten isomorphic substitution with rhenium in wolframite is studied. The appearance of rhenium-bearing wolframite is caused by specific conditions of the crystallization of rare-metal granite magmas.

Here is considered local melting events realizable under nonequlibrium thermodynamic conditions and phase-structural transformations of materials produced by additive technology using steel powders of different chemical composition. The mechanism of formation of nano- and micro-particlesis, which are crystallization nucleus and hardening units is illustrated here. The formation of such particles occurs due to condensation mechanism in the sequence: steam – cluster – quasinanoparticle. The quality of obtained material is defined by the degree and quality of this process.