A. Steyerl

Viscosity effect on capillary waves at liquid interfaces

We discuss the viscosity damping effect on capillary waves in a binary-liquid system, using the linearized Navier-Stokes equation. The damping correction for the dispersion relation depends on the wave vector k as well as the interfacial tension. The calculated k-dependence of damping is characterized by a critical capillary-wave-number value , which separates the regions of weak and strong damping. The surface and interfacial roughnesses of a binary liquid system with large liquid depths are calculated and compared to experiments. Although the analysis has been restricted to the classical, macroscopic level, we obtain a noticeable modification from earlier hydrodynamic results for capillary wave damping and liquid-liquid interfacial roughness.

Neutron lifetime from a liquid walled bottle

The neutron lifetime has been measured in a storage experiment by counting the ultra-cold neutrons remaining in a fluid walled bottle as a function of the duration of storage. Wall losses are eliminated by varying the bottle volume to surface ratio. Our result is τβ = (887.6 ± 3) s.

Specular and diffuse reflection and refraction at surfaces

Abstract Reflection and refraction of waves at perfect and imperfect surfaces and interfaces is an old and vast topic with a wide range of applications ranging from geology to studies of the surface of distant planets and from sound waves to gamma-rays. Neutron and X-ray reflectometry constitute just one example. Information on the geometry, chemistry and magnetic field distribution at and near a surface is contained in the specularly reflected and transmitted beams as well as in the angular distribution of non-specular diffraction. We show that several methods of calculating these radiation fields provide equivalent results, and we extend the well-known methods applicable to beam incidence at large angles far exceeding the critical angle for total reflection, to the interesting regions of intermediary and subcritical angels.

Ultracold neutrons: Production and experiments☆

Abstract The research with ultracold neutrons has greatly profited from the new intense sources which have become operational in recent years. The strongest source available at present is the Turbine Source at the High-Flux Reactor of the Institut Laue-Langevin which provides a flux increase by more than an order of magnitude over previous facilities. We report on some of the experiments conducted at this source and discuss further possible applications of ultracold neutrons.

Ultracold Neutron Depolarization in Magnetic Bottles

We analyze the depolarization of ultracold neutrons confined in a magnetic field configuration similar to those used in existing or proposed magneto-gravitational storage experiments aiming at a precise measurement of the neutron lifetime. We use an extension of the semi-classical Majorana approach as well as an approximate quantum mechanical analysis, both pioneered by Walstrom et al. [Nucl. Instr. Meth. Phys. Res. A 599, 82 (2009)]. In contrast with this previous work we do not restrict the analysis to purely vertical modes of neutron motion. The lateral motion is shown to cause the predominant depolarization loss in a magnetic storage trap. The system studied also allowed us to estimate the depolarization loss suffered by ultracold neutrons totally reflected on a non-magnetic mirror immersed in a magnetic field. This problem is of preeminent importance in polarized neutron decay studies such as the measurement of the asymmetry parameter A using ultracold neutrons, and it may limit the efficiency of ultracold neutron polarizers based on passage through a high magnetic field.

Looking for surface states of ultra-cold neutrons

Abstract We report experiments testing the question whether or not ultra-cold neutrons (UCN) stored in traps with total-reflecting walls are temporarily adsorbed to the walls. A hypothetical process of sticking to the walls is theoretically intriguing but it can apparently make plausible the puzzling observations made in UCN storage experiments over the years.

Dynamics of pseudo-partial wetting studied by neutron reflectometry

Abstract The structural changes occurring in oil layers during condensation of deuterated octane (C 8 D 18 ) on the surface of a solid (single-crystal silicon) and a liquid (water solution with low (0.08 wt%) concentration of a non-ionic surfactant (C 10 E 4 ) have been studied by neutron reflectometry. The results demonstrate the presence of pseudo-partial wetting during condensation. The van der Waals attractive potential stabilizes a thin oil film coexisting with the residual droplet. We report a study of the growth dynamics of the residual droplet.

A multilayer ultracold neutron turbine source for a long-pulse spallation source

Abstract We have developed a concept for an ultracold neutron (UCN) turbine source based on a long-pulse spallation source. Using a single reflection from a receding blade, the turbine converts cold neutrons from the primary moderator to UCN. The UCN pulse length is spread out in time and is comparable to the primary pulse interval, producing a quasi-continuous UCN source. The principal parameters for such a design are the primary source pulse length, the flight path distance, and the velocity acceptance interval of the reflector. Taking advantage of recent advances in multilayer reflector preparation, we propose W11B4C multilayer reflectors with a high-reflectivity plateau in the velocity range of 80±5 m/s. We have simulated a multilayer turbine which converts 160±5 m/s neutrons from a 1 ms primary source with a 2.5 m incident flight path to UCN with an efficiency, in terms of phase space density, of about 4.4%. For a ∼1 MW long-pulse spallation source with 1 ms pulse length and 60 Hz frequency, and a time average flux in a liquid hydrogen moderator of 1 × 1014 n/cm2 s, this corresponds to a UCN source flux of 1.9 × 105 n/cm2 s, a total UCN current of 3.3 × 107 n/s, and a UCN density (for velocity ≤6.2 m/s) of 500 n/cm3.

Ultracold neutron turbine for the advanced neutron source

Abstract The paper describes a design for an ultracold neutron turbine source which has been developed for the planned Advanced Neutron Source at Oak Ridge. An “S”-shaped neutron guide transports very cold neutrons from a horizontal Cold Source to the turbine location. For the design neutron velocity of 40 m/s, this guide approaches the efficiency of a straight guide, while it filters strongly against neutrons with velocities above 60 m/s. The proposed turbine is designed for operation at a peripheral velocity of 20 m/s. This design speed, slower than that of existing turbines, has been chosen to minimize the effect of the circular turbine motion. The lower speed, coupled with the use of 58 Ni as the turbine blade material, allows a significant increase in performance with fewer blades.

Possible investigation of liquid-vapor phase transition with a realistic interface using long-wavelength neutrons

Abstract It is shown that the coexistence curve of a classical fluid ( 4 He as an example) with realistic interface profiles can be mapped with high precision, minimal gravity distortion, and to the immediate vicinity of the critical point by employing the interference of long wavelength neutrons from a thin film of the fluid.