AbstractThe results of calculation of fluxes of ultracold (UCNs), very cold, and cold neutrons at the output of neutron guides of the UCN source with superfluid helium at the WWR-M reactor are presented. UCN density ρ_35L = 1.3 × 10^4 n/cm^3 in the trap of the electric dipole moment (EDM) spectrometer was obtained by optimizing source parameters. This UCN density in the EDM spectrometer is two orders of magnitude higher than the UCN density at the output of the available UCN sources. The flux density of cold neutrons with a wavelength of 2–20 Å at the output of a neutron guide with a cross section of 30 × 200 mm^2 should be as high as 1.1 × 10^8 n/(cm^2 s), while the flux density of very cold neutrons (50–100 Å) at the output of the same neutron guide should be 2.3 × 10^5 n/(cm^2 s). An extensive program of fundamental and applied physical research was mapped out for this source.

The results of experimental verification of the feasibility of enhancing the efficiency of neutron-beam polarizers based on magnetized supermirrors are presented. The idea is to use both spin components of a neutron ensemble in a beam. The positive component is reflected from one magnetized mirror, and the negative component, which passes through it, is rotated by 180° and reflected from another mirror. Both beams were detected by a single detector. With the coefficients of reflection of spin components from the mirrors and the efficiency of rotation of the negative component factored in, an approximately twofold enhancement of the neutron intensity was obtained at an average polarization of ~66%. A monochromatic neutron beam was used in these experiments.

The results of experimental verification of the possibility of increasing the neutron beams luminosity of polarizing devices based on magnetized supermirrors are presented. The essence of the experiment is to use both components of the neutron spins in the beam. The positive component is reflected from one magnetized mirror, and the passing mirror opposite component after turning 180 degree is reflected from another similar mirror. Both beams were recorded with one detector. Taking into account the reflection coefficients of the components by the mirrors and the efficiency of the rotation of the opposite component, an increase in the neutron intensity was obtained approximately twice with an average polarization of about 66%. The experiments were performed on a monochromatic neutron beam.

The results of calculation of fluxes of ultracold (UCNs), very cold, and cold neutrons at the output of neutron guides of the UCN source with superfluid helium at the WWR-M reactor are presented. UCN density ρ35L = 1.3 × 104 n/cm3 in the trap of the electric dipole moment (EDM) spectrometer was obtained by optimizing source parameters. This UCN density in the EDM spectrometer is two orders of magnitude higher than the UCN density at the output of the available UCN sources. The flux density of cold neutrons with a wavelength of 2–20 Å at the output of a neutron guide with a cross section of 30 × 200 mm2 should be as high as 1.1 × 108 n/(cm2 s), while the flux density of very cold neutrons (50–100 Å) at the output of the same neutron guide should be 2.3 × 105 n/(cm2 s). An extensive program of fundamental and applied physical research was mapped out for this source.

The main directions of development of the project on the modernization and improvement of the REVERANS reflectometer, which is proposed to be installed at the PIK reactor (REVERANS-2), are described. They include the substitution of magnetic materials in instrument construction and the replacement of the autonomous table for samples; the equipment of the instrument with a polarimeter to measure the polarization components of incident and reflected neutron beams; and replacement of the electronics and mechanisms for moving the platforms. The REVERANS-2 parameters expected after modernization are given.

The closed porous structure in ceramic materials is investigated by spin-echo small-angle neutron scattering. A series of ceramic samples of oxygen–ion conductors based on bismuth molybdate with the general formula Bi 12.8 X 0.2 Mo 5 O 34 ± δ ( X = Mg, Ba, Ca, Sr) is obtained by powder sintering for 6−45 h at a temperature close to the melting point. The samples are characterized by scanning electron microscopy and X-ray fluorescence analysis. It is found that they had a stoichiometric chemical composition, are singlephase, and contain clean pores between crystal grains. The pore size is determined by spin-echo small-angle neutron scattering and ranges from 2.2 to 3.5 μm. It is demonstrated that longer sintering times correspond to larger pores (the increase in their average diameter is as large as 30%). It is found that the studied materials lack a fractal pore structure.

We made software to simulate Larmor precession in a setup for SESANS with adiabatic/RF flippers in magnets, existing at PNPI. The final polarisation of a divergent “gribbon beam” of height 2 cm is calculated as a function of λ. For λ = 6 Å, flippers 56 cm apart and RF frequency 1 MHz we find spin-echo length δ = 0.9 δm. We show numerically, how λ is converted to δ. Extension to δ = 20 δm is realistic.

A device that forms a vertically diverging neutron beam is described. The device allows scanning at the angle of incidence of neutrons on a fluid surface in a reflectometer with a vertical scattering plane. Computer simulation of the former is carried out, and the beam characteristics (horizontal and vertical divergences and the neutron energy spectrum) are obtained. These characteristics are compared with experimental data. Three units are the main advantages of the former: specially fabricated input and output collimators and neutron filters. The reasons for differences in the experimental and simulated data are discussed.

The possibility of application of a foil with an electric current to modulate a beam of polarized neutrons to measure their spectrum is discussed. The experimental results of this application are presented for the measurement of spectra with various wavelength distributions of neutrons. The advantages of this chopper are noted.

We discuss the present status and the prospects of Spin-Echo Small-Angle Neutron Scattering (SESANS) against the background of the available expertise and the neutron source PIK at PNPI (Gatchina). Two options for SESANS instruments are reviewed: (1) monochromatic with π-flipping permalloy foils and (2) with adiabatic radio frequency spin flippers in a white beam, combined with time-of-flight data collection. A software tool for quantitative prediction of the technical properties of option (2) is developed. For both options, we show that a SESANS instrument which can compete with instruments elsewhere, is realistic. For option (2), we suggest a perspective of spin-echo-length range such that neutron interference experiments become feasible.

The results of the first experiments with a spin-echo small-angle neutron scattering (SESANS) device built at the VVR-M reactor at the St. Petersburg Institute of Nuclear Physics (Gatchina) are presented. SESANS utilizes the possibilities of the spin-echo method for determining the structural characteristics of materials in real space with on the 10–104-nm length scale. Validation measurements are conducted using SiO2 colloidal particles. Samples of SiO2 spheres with a diameter determined through scanning electron microscopy and synchrotron-radiation ultra-small-angle scattering are used for calibration of the device. Approximation of the data obtained with the SESANS device was conducted using the autocorrelation function for dilute monodisperse spheres. The sizes of the spheres determined via SESANS are in agreement with those determined by other methods within the experimental error.

The behavior of a magnetic flux in a ceramic high-temperature superconductor with rotation of a magnetic field through a specified angle has been investigated using polarized neutrons. Two models of penetration of a weak magnetic field into a granular superconductor have been discussed. Based on the obtained distributions of the rotation angle and the magnitude of the magnetic field inside the sample, the choice is made in favor of one of these models.

The most detailed and reliable information about the magnetic state (magnetization depth profiles) of layers can be obtained by neutron reflectometry with vector polarization analysis. Two schemes of realization of this technique are considered. Precession coils designed to manipulate the polarization vector of monochromatic beams are used in scheme I. This scheme was tested at the neutron reflectometer NR-4M (PNPI, Gatchina). The earliest experimental data on the polarization vector rotation are reported, giving direct evidence of the wave function phase shift of a massive particle, the neutron, under total reflection. The basic elements for scheme II are remanent supermirrors. This scheme is designed for use with a white beam and is advantageous for pulse neutron sources. The effect of stray fields produced by remanent supermirrors on the neutron polarization has been theoretically and experimentally evaluated; efficient ways of compensating the stray fields are proposed.

The Pd1−x Fe x )0.95Mn0.05 alloy with random competing interaction was studied by measuring the muon spin relaxation in an external transverse magnetic field and in a zero magnetic field. Using the measured temperature dependence of the dynamic relaxation rate λ and the characteristics of the distribution of local static fields, the phase states of the sample under study are refined. In particular, it is shown that the ferromagnetic and spin-glass states coexist simultaneously in the sample below 25 K. Combined studies of the sample using the μSR and neutron depolarization methods made it possible to determine the size of magnetic inhomogeneities to be 2–6 μm in the temperature range 5–40 K.

To study the free surface of liquids, a Reverans reflectometer with a vertical neutron scattering plane has been designed and is fabricated at Petersburg Nuclear Physics Institute. This reflectometer is intended to investigate surfaces and interfaces in liquid magnetic or nonmagnetic systems. The principles of reflectometer operation are described. The general view of the reflectometer with ready units is presented and its main technical parameters are given. The results of preliminary tests are reported.