A.A. van Well

Double-disk chopper for neutron time-of-flight experiments

Abstract A chopper consisting of two coupled disks is described. It produces neutron pulses with a wavelength-dependent burst time. In a large wavelength range the burst time is, in good approximation, proportional to the neutron wavelength.

Non-analytic dispersion relations in liquid argon

Abstract Neutron scattering experiments on liquid argon reveal an anomalous approach to the hydrodynamic limit for the frequency of sound and for the ratio of the sound and heat mode damping factors. In both cases the behavior agrees with non-analytic dispersion relations predicted by the mode coupling theory.

ROG, the neutron reflectometer at IRI, Delft

Abstract A description is given of an optimally designed neutron reflectometer. The background to the design is explained, calibration measurements are discussed and data handling procedures are described. Finally, the possibilities of the reflectometer are shown with several reflectivity measurements.

Structure of grafted polymers, investigated with neutron reflectometry

Neutron reflectometry is used to investigate the structure of polymers end-grafted to an interface at high grafting densities, so-called brushes. Our system consists of polystyrene-polyethyleneoxide (PS-PEO) diblock copolymers, irreversibly adsorbed at the air/D2O interface. At relatively low grafting densities the density profile of a monodisperse brush is block-like, with a tail region in which the density smoothly decays towards zero. At high grafting density the profile is predominantly parabolic. Bimodal brushes are examined for several length ratios and mixing ratios. At a given grafting density the extension of the long chains is larger in a bimodal brush than in a monodisperse. This additional extension increases with increasing length and fraction of small chains. Good agreement is found between the density profiles obtained from analysis of the neutron reflectometry data and profiles predicted by the Scheutjens–Fleer self-consistent-field model.

Ex situ reflection mode EXAFS at the Ti K-edge of lithium intercalated TiO2 rutile

Abstract The near surface structure of Li-intercalated rutile TiO2-electrodes was investigated with grazing incidence reflection mode XAFS (EXAFS and XANES) spectroscopy. Though real in situ experiments are not feasible due to the extremely strong parasitic absorption of the electrolyte, a new cell was constructed which enables the electrochemical processing of samples which are sensitive towards oxidation as well as it permits reflection mode X-ray experiments after the controlled emersion of the electrodes from the electrolyte. Our results show that even Li containing electrolytes and Li intercalated electrodes can be processed inside the cell. During the electrochemical Li intercalation in rutile, only a thin surface layer of some few nm thickness was changed by the lithiation, the thickness of which is increasing with decreasing intercalation potential. A detailed XANES and EXAFS data analysis gives strong evidence that the structure of this layer is identical compared to that of polycrystalline Li-titanate Li0.6TiO2 (anatase type space group imma).

Design and performance of a novel neutron powder diffractometer: PEARL at TU Delft

The performance of the new neutron powder diffraction instrument PEARL that is installed at the research reactor of Delft University of Technology is reported. It is based on the optimization concepts developed by Cussen [Nucl. Instrum. Methods Phys. Res. Sect. A (2007), 583, 394–406], which lead to high performance competing with existing constant-wavelength neutron powder diffractometers, despite the relatively low source brightness of the 2 MW reactor of Delft University of Technology.

Observation of the Zeeman splitting for neutrons reflected by magnetic layers

Abstract The Zeeman splitting was measured for neutrons specularly reflected from a magnetic layer in a particular geometry. The neutron spins were quantized along an external magnetic field H, and the reflecting layer was magnetized in a different direction, causing some of the reflected neutrons to flip spin. The laws of conservation of energy and momentum for the spin-flipped neutrons impose the condition θf2 = θi2 ± 1.47 × 10−7 Hλ2, where θi, θf are, respectively, the incident and reflected angles in radians, H is expressed in kOe and λ (the neutron wavelength) in A. Spin-flipped neutrons are reflected at an angle significantly different from the angle of incidence even in fields of a few kOe, although the Zeeman splitting energy amounts to less than 10−7 eV.

ROG, the new neutron reflectometer at IRI, Delft

Abstract A description is given of the neutron reflectometer ROG, recently installed at IRI. The neutron wavelength is determined by time of flight. Wavelengths from 0.08 to 0.8 nm can be used. First experimental results are presented.

Quasi-in-situ reflection mode XANES at the Ti K-edge of lithium intercalated TiO2 rutile and anatase

Abstract The near surface structure of Li-intercalated rutile and anatase TiO 2 electrodes was investigated with grazing incidence reflection mode XANES spectroscopy. Though real in situ experiments are not feasible due to the extremely strong parasitic absorption of the electrolyte, a new cell was constructed. It enables the electrochemical processing of samples which are sensitive to oxidation as well as it permits reflection mode X-ray experiments after the controlled emersion of the electrodes from the electrolyte. Our results show that even Li containing electrolytes and Li intercalated electrodes can be processed inside the cell. During the electrochemical Li intercalation in rutile, only a thin surface layer of some few nm thickness was changed by the lithiation. The structure of this layer seems to have a similar structure compared to the Li titanate Li 0.6 TiO 2 (space group imma). The anatase layer could be fully intercalated showing the characteristic Li-titanate structure. In the surface region the Li intercalation results in an edge shift that corresponds to Ti 3+ states in contrast to the Ti 3.4+ states in the bulk.

Testing a multilayer mirror system in use for polarised neutrons

Abstract The transmission of a curved system of multilayers is investigated theoretically as well as experimentally. The new feature of this work is the consideration of different indices of reflection on both sides of the mirrors. It appears that the experimental result is systematically by about 30% lower as theoretically expected, which most probably is due to the imperfect planeness of the mirror.