Peculiarities of neutron waveguides with thin Gd layer

Peculiarities of the formation of a neutron enhanced standing wave in the structure with a thin highly absorbing layer of gadolinium are considered in the article. An analogue of the poisoning effect well known in reactor physics was found. The effect is stronger for the Nb/Gd/Nb system. Despite of this effect, for a Nb/Gd bilayer and a Nb/Gd/Nb trilayer placed between Al2O3 substrate and Cu layer, it is shown theoretically and experimentally that one order of magnitude enhancement of neutron density is possible in the vicinity of the Gd layer. This enhancement makes it possible to study domain formation in the Gd layer under transition of the Nb layer(s) into the superconducting state (cryptoferromagnetic phase).Comment: 5 pages, 2 figure

Raduga experiment: Multizonal photographing the Earth from the Soyuz-22 spacecraft

The main results of the scientific research and 'Raduga' experiment are reported. Technical parameters are presented for the MKF-6 camera and the MSP-4 projector. Characteristics of the obtained materials and certain results of their processing are reported

A hydrodynamic model for asymmetric explosions of rapidly rotating collapsing supernovae with a toroidal atmosphere

We numerically solved the two-dimensional axisymmetric hydrodynamic problem of the explosion of a low-mass neutron star in a circular orbit. In the initial conditions, we assumed a nonuniform density distribution in the space surrounding the collapsed iron core in the form of a stationary toroidal atmosphere that was previously predicted analytically and computed numerically. The configuration of the exploded neutron star itself was modeled by a torus with a circular cross section whose central line almost coincided with its circular orbit. Using an equation of state for the stellar matter and the toroidal atmosphere in which the nuclear statistical equilibrium conditions were satisfied, we performed a series of numerical calculations that showed the propagation of a strong divergent shock wave with a total energy of 0.2x10^51 erg at initial explosion energy release of 1.0x10^51 erg. In our calculations, we rigorously took into account the gravitational interaction, including the attraction from a higher-mass (1.9M_solar) neutron star located at the coordinate origin, in accordance with the rotational explosion mechanism for collapsing supernovae.W e compared in detail our results with previous similar results of asymmetric supernova explosion simulations and concluded that we found a lower limit for the total explosion energy.Comment: 13 pages, 5 figures, 2 table

Magnetic and Superconducting Phase Diagram of Nb/Gd/Nb trilayers

We report on a study of the structural, magnetic and superconducting properties of Nb(25nm)/Gd($d_f$)/Nb(25nm) hybrid structures of a superconductor/ ferromagnet (S/F) type. The structural characterization of the samples, including careful determination of the layer thickness, was performed using neutron and X-ray scattering with the aid of depth sensitive mass-spectrometry. The magnetization of the samples was determined by SQUID magnetometry and polarized neutron reflectometry and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The analysis of the neutron spin asymmetry allowed us to prove the absence of magnetically dead layers in junctions with Gd interlayer thickness larger than one monolayer. The measured dependence of the superconducting transition temperature $T_c(d_f)$ has a damped oscillatory behavior with well defined positions of the minimum at $d_f$=3nm and the following maximum at $d_f$=4nm; the behavior, which is in qualitative agreement with the prior work (J.S. Jiang et al, PRB 54, 6119). The analysis of the $T_c(d_f)$ dependence based on Usadel equations showed that the observed minimum at $d_f$=3nm can be described by the so called "$0$" to "$\pi$" phase transition of highly transparent S/F interfaces with the superconducting correlation length $\xi_f \approx 4$nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures with $d_f \sim \xi_f$ which are of topical interest in superconducting spintronics

On the feasibility to study inverse proximity effect in a single S/F bilayer by Polarized Neutron Reflectometry

Here we report on a feasibility study aiming to explore the potential of Polarized Neutron Reflectometry (PNR) for detecting the inverse proximity effect in a single superconducting/ferromagnetic bilayer. Experiments, conducted on the V(40nm)/Fe(1nm) S/F bilayer, have shown that experimental spin asymmetry measured at T = 0.5TC is shifted towards higher Q values compared to the curve measured at T = 1.5TC. Such a shift can be described by the appearance in superconducting vanadium of magnetic sub-layer with thickness of 7 nm and magnetization of +0.8 kG.Comment: Changes in the 2nd version: small mistypes are corrected. Manuscript submitted to JETP let. 4 pages, 2 figure

A Rotating Collapsar and Possible Interpretation of the LSD Neutrino Signal from SN 1987A

We consider an improved rotational mechanism of the explosion of a collapsing supernova. We show that this mechanism leads to two-stage collapse with a phase difference of \sim 5 h. Based on this model, we attempt a new interpretation of the events in underground neutrino detectors on February 23, 1987, related to the supernova SN 1987A.Comment: 18 pages, 3 figures, 9 table

Photon emission from bare quark stars

We investigate the photon emission from the electrosphere of a quark star. It is shown that at temperatures T\sim 0.1-1 MeV the dominating mechanism is the bremsstrahlung due to bending of electron trajectories in the mean Coulomb field of the electrosphere. The radiated energy for this mechanism is much larger than that for the Bethe-Heitler bremsstrahlung. The energy flux from the mean field bremsstrahlung exceeds the one from the tunnel e^{+}e^{-} pair creation as well. We demonstrate that the LPM suppression of the photon emission is negligible.Comment: 35 pages, 5 figure

Magnetic proximity effect in [Nb/Gd] superlattices seen by neutron scattering

We have used spin-polarized neutron reflectometry to investigate the magnetization profile of superlattices composed of ferromagnetic Gd and superconducting Nb layers. We have observed a partial suppression of ferromagnetic (F) order of Gd layers in [Gd($d_F$)/Nb(25nm)]$_{12}$ superlattices below the superconducting (S) transition of the Nb layers. The amplitude of the suppression decreases with increasing $d_F$. By analyzing the neutron spin asymmetry we conclude that the observed effect has an electromagnetic origin - the proximity-coupled S layers screen out the external magnetic field and thus suppress the F response of the Gd layers inside the structure. Our investigation demonstrates the considerable influence of electromagnetic effects on the magnetic properties of S/F systems