New measurements of the neutron electric dipole moment

We report a new measurement of the neutron electric dipole moment with the PNPI EDM spectrometer using the ultracold neutron source PF2 at the research reactor of the ILL. Its first results can be interpreted as a limit on the neutron electric dipole moment of |d _n | < 5.5 × 10^?26 e cm (90% confidence level).     

Search for sterile neutrinos in the neutrino-4 experiment

An experimental search for sterile neutrinos has been carried out at a neutrino facility based on the SM-3 nuclear reactor in Dimitrovgrad, Russia. The movable detector with passive shielding against the external radiation may be positioned at a distance varying between 6 and 12 m from the center of the reactor. The antineutrino flux has for the first time been measured using a movable detector placed close to the antineutrino source. The accuracy of the measurements is largely restricted by the cosmic background. The results of the measurements performed at small and large distances are analyzed in terms of the sterile-neutrino model parameters Δm ₁₄ ² and sin²2θ₁₄.     

A Complex Approach to Noninvasive Estimation of Microcirculatory Tissue Impairments in Feet of Patients with Diabetes Mellitus using Spectroscopy

We investigate conditions for the occurrence of a bistable response from a thin layer of an ensemble of two-level inhomogeneously broadened emitters upon their interaction with resonant radiation. A Lorentz correction to the local field that acts on emitters is taken into account. Bistability phase diagrams in the parameter space (inhomogeneous broadening, detuning away from resonance, and local field) are calculated, and the occurrence of optical hysteresis of the system is demonstrated. In addition to this, we study the switching time from the lower stable branch of the bistable characteristics to the upper one and vice versa against the intensity of the driving field, which determines the operation speed of a bistable device. The possibility of using a thin layer of resonant emitters as a multichannel all-optical switch is discussed.     

Evaluated integral cross sections of the <Superscript>7</Superscript>Li(<Emphasis Type="Italic">p</Emphasis>, α)<Superscript>4</Superscript>He reaction

New data on the energy dependence of integral cross sections of the ⁷Li(p, α)⁴He reaction are obtained to develop the SaBa (Sarov Base) library of evaluated and experimental nuclear data at the Russian Federal Nuclear Center, All-Russia Research Institute of Experimental Physics [1]. The sum of smooth and resonance parts is used as an approximating function in the current version of the SaBa database. The smooth part is described by cubic splines. Lorentzians are used to describe resonance regions. Experimental data already available in the SaBa library are analyzed to obtain new evaluated data on the ⁷Li(p, α)⁴He reaction, and a search is conducted for new data in domestic and foreign literary sources.     

Synthesis and properties of polyvinylidene fluoride high-temperature treatment products

Simultaneous thermal, gravimetric and mass spectrometric analyses made it possible to reveal considerable differences in fluorine desorption and changes in weight of filmy samples of original and partly chemically dehydrofluorinated polyvinylidene fluoride (PVDF) under an increase in temperature up to 800°C in argon flow. To determine the thermal treatment effect on the final material’s properties, the PVDF film was heated in a backing vacuum (0.5 Torr) up to 600°C with 40-minute isothermal exposure at a maximum temperature. Raman scattering spectroscopy was applied to compare molecular structures of the final products obtained by the high-temperature treatment of all samples and to prove their similarity. The spectrum of the chemically dehydrofluorinated sample, not subjected to a thermal effect, was characterized by a weak band in the region of 2000–2200 cm^–1, characteristic of the carbyne-like structures dominated by a polyyne type.

     

On the Possibility of Measuring the Ratio GA/GV by means of Polarized Ultracold Neutrons

The possibility of experimentally determining the ratio λ of the axial weak-interaction constant G_A to the vector weak-interaction constant G_V by simultaneously measuring the electron and neutrino asymmetries at the same setup is discussed. The proposed measurement and data-processing procedures are described in detail. The determination of λ by the method in question permits disregarding the possible contribution of the Fierz interference term and dispensing with an accurate measurement of the neutron polarization. It is shown that this method makes it possible to measure λ to a precision at a level of 10⁻⁴.

     

Experimental search for neutron–mirror neutron oscillations using storage of ultracold neutrons

The idea of a hidden sector of mirror partners of elementary particles has attracted considerable interest as a possible candidate for dark matter. Recently it was pointed out by Berezhiani and Bento that the present experimental data cannot exclude the possibility of a rapid oscillation of the neutron n to a mirror neutron n′ with oscillation time much smaller than the neutron lifetime. A dedicated search for vacuum transitions n→n^′$\mathrm{n}\to {\mathrm{n}}^{\prime }$ has to be performed at weak magnetic field, where both states are degenerate. We report the result of our experiment, which compares rates of ultracold neutrons after storage at a weak magnetic field well below 20 nT and at a magnetic field strong enough to suppress the seeked transitions. We obtain a new limit for the oscillation time of n–n′ transitions, τosc(90% C.L.)>414 s${\tau }_{\mathrm{osc}}(90\mathrm{\%}\text{C.L.})>414\text{s}$. The corresponding limit for the mixing energy of the normal and mirror neutron states is δm(90% C.L.)<1.5×¹⁰⁻¹⁸ eV$\delta m(90\mathrm{\%}\text{C.L.})<1.5\times {10}^{\mathrm{-18}}\text{eV}$.     

New Phases in the Lithiumnitridovanadate System — The Solid Solution Li7‐2xMgx[VN4] with 0 ≤ x ≤ 1

Solid solution phases Li_7‐2xMg_x[VN₄] (0 < x ≤ 1) with varying Mg‐content are obtained as yellow microcrystalline powders from heat treatment of mixtures of VN, Li₃N and Mg₃N₂ or from mixtures of Li₇[VN₄] and Mg₃N₂ at 1370 K in N₂ atmosphere at ambient pressure. At substitution parameter values of x > 0.5 a subsequent distortion from the ideal cubic unit cell to an orthorhombic unit cell is observed. The crystal structure of Li_7‐2xMg_x[VN₄] with x ≈ 1 was refined from neutron and X‐ray powder diffraction data (space group Pbca, No. 61, a = 963.03(3) pm, b = 958.44(3) pm, c = 951.93(2) pm, neutron pattern 14° — 156° 2θ, step non‐linear ≈ 0.0782° 2θ, No. of measured points 1816, R_p = 0.089, R_wp = 0.115, R_Bragg = 0.155, R_F = 0.114; X‐ray pattern 10° — 98° 2θ, step 0.005° 2θ, No. of measured points 17600, R_p = 0.028, R_wp = 0.045, R_Bragg = 0.113, R_F = 0.133, structure variables: 45). The crystal structure resembles a Li₂O type superstructure with the atomic arrangement of β‐Li₇[VN₄] and with two crystallographic Li‐sites each substituted by Mg with statistical occupation factors of 0.5. Chemical analyses prove the composition and XAS spectroscopy at the V K‐edge support the +5 oxidation state assignment for vanadium. XAS data also support the tetrahedral coordination of vanadium by N as indicated by the structure refinements.     

Synthesis,Crystal Structure and Lithium Motion of Li8SeN2 and Li8TeN2

The compounds Li₈EN₂ with E = Se, Te were obtained in form of orange microcrystalline powders from reactions of Li₂E with Li₃N. Single crystal growth of Li₈SeN₂ additionally succeeded from excess lithium. The crystal structures were refined using single‐crystal X‐ray diffraction as well as X‐ray and neutron powder diffraction data (I4₁md, No. 109, Z = 4, Se: a = 7.048(1) Å, c = 9.995(1) Å, Te: a = 7.217(1) Å, c = 10.284(1) Å). Both compounds crystallize as isotypes with an anionic substructure motif known from cubic Laves phases and lithium distributed over four crystallographic sites in the void space of the anionic framework. Neutron powder diffraction pattern recorded in the temperature range from 3 K to 300 K and X‐ray diffraction patterns using synchrotron radiation taken from 300 K to 1000 K reveal the structural stability of both compounds in the studied temperature range until decomposition. Motional processes of lithium atoms in the title compounds were revealed by temperature dependent NMR spectroscopic investigations. Those are indicated by significant changes of the ⁷Li NMR signals. Lithium motion starts for Li₈SeN₂ above 150 K whereas it is already present in Li₈TeN₂ at this temperature. Quantum mechanical calculations of NMR spectroscopic parameters reveal clearly different environments of the lithium atoms determined by the electric field gradient, which are sensitive to the anisotropy of charge distribution at the nuclear sites. With respect to an increasing coordination number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), and Li(1), respectively, the values of the electric field gradients decrease. Different environments of lithium predicted by quantum mechanical calculations are confirmed by ⁷Li NMR frequency sweep experiments at low temperatures.