Superfluid dynamics in neutron star crusts

A simple description of superfluid hydrodynamics in the inner crust of a neutron star is given. Particular attention is paid to the effect of the lattice of nuclei on the properties of the superfluid neutrons, and the effects of entrainment, the fact that some fraction of the neutrons are locked to the motion of the protons in nuclei

EXPERIMENTAL DETERMINATION OF EXCHANGE INTEGRALS IN MAGNETITE

De nouvelles expériences de diffusion inélastique de neutrons, au moyen d'un spectromètre à 3 axes, conduisent à une meilleure connaissance des intégrales d'échange dans la magnétite. De nouvelles branches ont été observées. Leurs fréquences peuvent être très bien ajustées dans le modèle d'Heisenberg, mais pas leurs intensités.New experiments of inelastic neutron scattering, by means of a triple-axis spectrometer, lead to a better knowledge of the exchange integrals in magnetite. New optical branches have been observed. Their frequencies may very well be fitted in the Heisenberg model, but not their intensities

Dense packing of molecular hydrogen in a porous hydride and the value of in situ diffraction studies of gas adsorption

Nanoporous materials have attracted great attention for gas storage, however, high volumetric storage capacity remains still a challenge. We investigate [1] a magnesium borohydride framework with small pores and a unique partially negatively-charged non-flat interior for hydrogen and nitrogen uptake by using neutron powder diffraction, volumetric gas adsorption, inelastic neutron scattering, and first-principles calculations. Hydrogen and nitrogen occupy distinctly different adsorption sites in the pores with very different limiting capacities: 2.33 H2 and 0.66 N2 per Mg(BH4)2. Molecular hydrogen is packed extremely dense with about twice the density of liquid hydrogen (144 g H2/L of pore volume), independently measured by three experimental methods. A penta-dihydrogen cluster is discovered where H2 molecules in one position have rotational freedom whereas in another have a well-defined orientation and a directional interaction with the framework. This study [1] reveals that densely packed hydrogen can be stabilized in small-pore materials at ambient pressures. Studies of physisorbed hydrogen require the use of neutron powder diffraction. For heavier molecules, in situ X-ray powder diffraction allows to study adsorption thermodynamics and kinetics [2, 3], revealing simultaneously the microscopic origins of guest-host and guest-guest interactions. (Quasi)-equilibrium isotherms and isobars can be built directly from sequential Rietveld refinements, both on adsorption and desorption, thus addressing the hysteresis and kinetics of gas adsorption/desorption. Detailed picture of guest reorganization with an increasing uptake can be obtained. [1] H. Oh, …, Y. Filinchuk, Small-pore hydridic frameworks store densely packed hydrogen. Nature Chem., 2024, DOI: https://doi.org/10.1038/s41557-024-01443-x [2] I. Dovgaliuk, V. Dyadkin, M. Vander Donckt, Y. Filinchuk, D. Chernyshov, ACS Appl. Mater. Interfaces 12, 2020, 7710. [3] I. Dovgaliuk, I. Senkovska, X. Li, V. Dyadkin, Y. Filinchuk, D. Chernyshov, Angew. Chem. Int. Ed., 60, 2021, 5250

Multi-milliampere compact cyclotrons used as neutron sources

Recent developments in accelerator technology enable high current proton or deuteron beams production up to several milliamps, providing attractive sources for high neutron yield production. Be(p,n), Be(d,n) and /sup 238/U(X,n) reactions are discussed to produce high energy and thermal neutron yields. A 140 MeV, 2.5 mA extracted beam cyclotron is also proposed to feed a spallation neutron source, generating thermal neutron fluxes similar in intensity to those produced by nuclear reactors.Anglai

Production by \Sigma

Introduction The inclusive production of \Xi \Gamma --Hyperons in high energy collisions of different hadrons with target nuclei allows to study the role of the projectile valence quarks in the production process. It gives therefore insight in the physics of the hadronisation process. The inclusive production of hyperons has been studied mostly in proton-- and neutron--beams [1][7]. \Xi \Gamma --production in \Xi \Gamma --Be-- and \Xi \Gamma --N-- interactions was measured in a previous experiment with the SPS charged hyperon beam at CERN [11,12]. The measurements were performed in different kinematical regions and therefore a comparison of the different results is difficult. The WA89 experiment gives the opportunity to measure the \Xi \Gamma --production under homogeneous conditions with different types of beam particles on several targets. 2. Experiment WA89 The Experiment WA89 (Fi