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We report a measurement of the reflection of ultracold neutrons from flat, large-area plates of different Fermi potential materials with low surface roughness. The results were used to test two diffuse reflection models, the well-known Lambert model and the micro-roughness model which is based on wave scattering. The Lambert model fails to reproduce the diffuse reflection data. The surface roughness b and correlation length w , obtained by fitting the micro-roughness model to the data are in the range 1 $ \le$ b $ \le$3 nm and 10 $ \le$ w $ \le$120 nm, in qualitative agreement with independent measurements using atomic force microscopy. [ABSTRACT FROM AUTHOR]

Abstract: The Fermi potential V f of diamond-like carbon (DLC) coatings produced with laser-controlled vacuum arc deposition and that of diamond, Al, Si, Be, Cu, Fe and Ni was measured using two different methods, (i) transmission of slow neutrons through foils in a time-of-flight experiment and (ii) cold neutron reflectometry (CNR). For diamond-like carbon in transmission we obtain V f =(249±14)neV. This is approximately the same as for beryllium and consistent with the theoretical expectations for the measured diamond (sp3) content of 45%. For an sp3-content of 67%, we find V f =(271±13)neV from reflectometry, again in agreement with theory. These findings open new perspectives in using DLC as storage volume and neutron guide coatings for ultracold neutron sources. [Copyright &y& Elsevier]

Abstract: We have produced hydrogen-free diamond-like carbon (DLC) films by vacuum arc deposition for use as wall coating material in ultracold neutron (UCN) applications. The sp3 fraction, the main quality factor for DLC used in UCN applications, was varied from 0.4 to 0.9, the coating thickness between 10 nm and 120 nm. The samples were characterized by using X-ray Absorption Near-Edge Spectroscopy (XANES), X-ray induced Photoelectron Spectroscopy (XPS), Laser induced surface Acoustic Waves (LAwave), cold neutron reflectometry and Raman spectroscopy at visible excitation wavelength. We observe reasonable agreement between the different results for film thicknesses below 20 nm. For larger thickness, we find that the surface-sensitive methods XPS and XANES yield smaller sp3 fractions (by up to 20%) than the bulk-sensitive LAwave, being consistent with the assumption of a lower-density surface layer on a nominal-density bulk layer. [Copyright &y& Elsevier]

Abstract: To complete our study of ultracold neutron (UCN) storage-vessel coatings, we have measured the Fermi potential for neutrons on diamondlike carbon coatings produced by laser induced vacuum arc deposition. A sample with an sp3 content of 0.45, measured using, for the first time, neutron transmission had a Fermi potential of . A second sample with an sp3 fraction of 0.67, measured using cold neutron reflectometry, gave . These values complete the demonstration that there is a viable alternative to Be in UCN physics. [Copyright &y& Elsevier]

Abstract: The GEANT4 code has been adapted to include the influence of gravity and inhomogeneous, slowly time-varying magnetic fields on neutrons. Ultracold neutrons (UCN) are introduced as a new class of particles. All relevant processes for the interactions at material boundaries and inside materials are implemented. The GEANT4 environment allows for an effective handling of complicated geometries. [Copyright &y& Elsevier]

Abstract: We describe the production, characterization and performance of magnetron-sputtered Be coatings on aluminum, copper and stainless steel substrates. The coating thickness is typically 300nm. Small samples were characterized by means of Optical Microscopy (OM), Atomic Force Microscopy (AFM) and X-ray induced Photoelectron Spectroscopy (XPS) and Elastic Recoil Detection Analysis (ERDA). The coating quality and adhesion following thermal cycling and neutron irradiation were tested with respect to future applications as storage containers in Ultracold Neutron (UCN) sources. The fractional uncoated area was determined to be 10−4 to 10−5 by OM and XPS. These results were confirmed by foil transmission measurements with UCN in the energy range 180 to 230neV. The storage time of a 250l Be-coated Cu container was determined for UCN energies up to 60neV at room temperature and around 90K and the wall loss factor η extracted. We obtained η (90K)=2.7×10−5 and η(300K)=1.1×10−4 in good agreement with previously published results. [Copyright &y& Elsevier]

Abstract: For the first time, ultracold neutrons have been stored in a volume formed of foils coated with diamond-like carbon. The coefficients for loss, η, and depolarization, β, per wall collision were determined simultaneously. The results for different samples, and , are among the best values measured for high Fermi potential materials without elaborate surface pre-treatment. Thin foil storage material will be widely applicable, e.g., in neutron β-decay studies. [Copyright &y& Elsevier]

Abstract: We have built a novel apparatus for the investigation of materials for the storage of ultracold neutrons. Neutrons are filled into a storage volume, confined at the bottom by a magnetic field, at the top by gravity and at the sides by the slit-less sample surface under investigation. For different beryllium and diamond-like carbon samples, storage times up to 200s were obtained at room temperature. The corresponding loss parameters for ultracold neutrons varied between 4.2 and per wall collision. [Copyright &y& Elsevier]

Abstract: Solid deuterium (sD) is a favourite converter material for the production of ultra-cold neutrons (UCN) in the next generation of UCN sources. In order to investigate sD properties relevant for this purpose, an apparatus for the preparation and characterization of ortho-D crystals has been built. It will be used for measurements of neutron transmission and scattering cross-sections as well as irradiation experiments with simultaneous optical control of the target conditions. The present paper describes the main components of the apparatus, i.e. the cryogenic optical D cell, the gas system, the optical photography system and the Raman spectroscopy system. [Copyright &y& Elsevier]