Tobias Panzner

Optical properties of boron carbide near the boron K edge evaluated by soft-x-ray reflectometry from a Ru/B 4 C multilayer

Soft-x-ray Bragg reflection from two Ru/B(4)C multilayers with 10 and 63 periods was used for independent determination of both real and imaginary parts of the refractive index n = 1 - delta + ibeta close to the boron K edge (approximately 188 eV). Prior to soft x-ray measurements, the structural parameters of the multilayers were determined by x-ray reflectometry using hard x rays. For the 63-period sample, the optical properties based on the predictions made for elemental boron major deviations were found close to the K edge of boron for the 10-period sample explained by chemical bonding of boron to B(4)C and various boron oxides.

Focusing neutrons with a combination of parabolic and elliptical supermirrors

Cold-neutron focusing is a challenge with regard to improving the flux at the sample, decreasing measurement time and/or gaining statistical reliability. Several techniques are used for neutron focusing, such as simple or multi-beam collimation, refractive or magnetic lenses, and focusing mirrors. In this work, a new device for focusing neutrons using a combination of a parabolic supermirror, an asymmetric slit system and an elliptical supermirror is presented. The aim of this focusing system is to improve the neutron flux at the sample compared to other techniques without either achromatism or absorption. The performance of the device obtained by simulations and measurements with a prototype on a small-angle neutron scattering setup shows a flux gain of four at the sample position and an intensity gain higher than 100 when the sample size can be increased compared to classical setups. Finally the applications for neutron instruments are commented on.

White beam x-ray waveguide optics

We report a white beam x-ray waveguide (WG) experiment. A resonant beam coupler x-ray waveguide (RBC) is used simultaneously as a broad bandpass (or multibandpass) monochromator and as a beam compressor. We show that, depending on the geometrical properties of the WG, the exiting beam consists of a defined number of wavelengths which can be shifted by changing the angle of incidence of the white x-ray synchrotron beam. The characteristic far-field pattern is recorded as a function of exit angle and energy. This x-ray optical setup may be used to enhance the intensity of coherent x-ray WG beams since the full energetic acceptance of the WG mode is transmitted.

Using parabolic supermirror lenses to focus and de-focus a neutron beam

We designed a focus/defocus neutron optics system, in order to investigate the performance, precision, efficiency, and operational and designing challenges of such coupled 2- lens systems, which could potentially find applications where small beam cross sections are beneficial, e.g., virtual neutron source concepts and high efficiency chopper systems. Our particular prototype (as described and discussed in this paper) has already been used in an on-going experiment, involving neutron spin filtering with dynamically polarized protons. After the designing and construction phases, we continued by performing a long series of simulations and measurements, in order to facilitate the alignment of the lenses, and investigate and understand the behaviour and output of the system. All measurements were performed at the BOA beamline at PSI. The simulations were particularly useful in aligning the lenses: tilts as small as 0.04° could easily be accounted for in our simulations and guide successfully the experimental aligning procedure of the first lens. Although harder to do in the case of two lenses, we were still able to reproduce fairly successfully with our simulations, tilts from both lenses. We have noticed (both in our experiments and simulations) that the sensitivity of such a set-up is ~ 0.01°.

Stresses and Strains in Cruciform Samples Deformed in Tension

The stress and strain relationship in the gauge region of six cruciform geometries is studied: the ISO standard geometry with slits in arms, two geometries with thinned gauge areas, two geometries with thinned gauge areas and slits in arms, and one modified ISO standard geometry with slits in arms and a thinned gauge area. For all the geometries, finite element simulations are performed under uniaxial loading to compare the plastic strain, the von Mises stress distribution and the in-plane stress evolution. Results show that less plastic strain can be achieved in the gauge of the two ISO standard geometries. For the remaining cruciform geometries, a strong non-linear coupling between applied forces in arms and gauge stresses is generated. The evolution of this non-linear coupling depends on the geometry type, applied biaxial load ratio and the elastic-plastic properties of the material. Geometry selection criteria are proposed to reduce this non-linear coupling.

X-ray and VIS light scattering from light-induced polymer gratings

Abstract Sinusoidally shaped surface relief gratings made of polymer films containing azobenzene moieties can be created by holographic illumination with laser light of about λ ≈ 500 nm. The remarkable material transport takes place at temperatures far (100 K) below the glass transition temperature of the material. As probed by visible light scattering the efficiency of grating formation crucially depends on the polarization state of the laser light and is maximal when circular polarization is used. In contrast to VIS light scattering X-ray diffraction is most sensitive for periodic surface undulations with amplitudes below 10 nm. Thus, combined in-situ X-ray and visible light scattering at CHESS were used to investigate the dynamics of surface relief grating formations upon laser illumination. The time development of grating peaks up to 9th order at laser power of P = 20 mW/cm2 could be investigated, even the onset of grating formation as a function of light polarization. A linear growth of grating amplitude was observed for all polarizations. The growth velocity is maximal using circularly polarized light but very small for s-polarized light.

Tailoring phase-space in neutron beam extraction

Abstract In view of the trend towards smaller samples and experiments under extreme conditions it is important to deliver small and homogeneous neutron beams to the sample area. For this purpose, elliptic and/or Montel mirrors are ideally suited as the phase space of the neutrons can be defined far away from the sample. Therefore, only the useful neutrons will arrive at the sample position leading to a very low background. We demonstrate the ease of designing neutron transport systems using simple numeric tools, which are verified using Monte-Carlo simulations that allow taking into account effects of gravity and finite beam size. It is shown that a significant part of the brilliance can be transferred from the moderator to the sample. Our results may have a serious impact on the design of instruments at spallation sources such as the European Spallation Source (ESS) in Lund, Sweden.

In Situ Neutron Diffraction and Acoustic Emission During the Biaxial Loading of AZ31 Alloy

The evolution of twinning in randomly textured magnesium alloy and rolled AZ31 alloy during biaxial mechanical tests has been monitored using concurrent application of acoustic emission and neutron diffraction methods. The influence of the loading path on twinning is discussed in detail. It is shown that the twinning is strongly sensitive to the load path.

Influence of the Loading Path on the Deformation Mechanisms of Magnesium Alloys

The evolution of deformation mechanisms in randomly textured magnesium alloy during uniaxial and biaxial mechanical tests has been monitored using concurrent application of acoustic emission and neutron diffraction methods. The influence of the loading path on both twinning and dislocation slip is discussed in detail. It is shown that both the twinning and non-basal slip are sensitive to the loading direction.

Neutron optics in cryogenic sample environment

Neutron focusing devices can be used to enhance neutron instruments when measuring small samples. However, for an optimum performance they need to be as close as possible to the sample which, in most situations, conflicts with the need for sample environment such as pressure cells, cryostats or magnets. In this paper we explore the potential and feasibility to incorporate a neutron lens based on supermirror technology into a cryostat containing a Paris-Edinburgh pressure cell. We present experimental results on the performance of super-mirrors between 5 and 300 K. Based on the experimental results we estimate the expected gain factors for a setup with a parabolic lens and a pressure cell in a cryogenic environment using Monte Carlo simulations.