G. Frei

Bio: G. Frei is an academic researcher from Paul Scherrer Institute. The author has contributed to research in topics: Neutron imaging & Neutron. The author has an hindex of 22, co-authored 38 publications receiving 2008 citations. Previous affiliations of G. Frei include United States Department of Energy.

The ICON beamline – A facility for cold neutron imaging at SINQ

Abstract: The beamline for Imaging with COld Neutrons (ICON) at Swiss spallation neutron source (SINQ) at Paul Scherrer Institut has a flexible design to meet the requests from a wide user community. The current status of the beamline and its characteristics are described. The instrumentation includes three experimental positions from which two are equipped with digital camera based imaging detectors. Tomographic imaging is among the standard methods available at the beamline. Advanced methods such as energy-selective imaging and grating interferometry are available as instrument add-ons which are easily installed.

Neutron Phase Imaging and Tomography

Abstract: We report how a setup consisting of three gratings yields quantitative two- and three-dimensional images depicting the quantum-mechanical phase shifts of neutron de Broglie wave packets induced by the influence of macroscopic objects. Since our approach requires only a little spatial and chromatic coherence it provides a more than 2 orders of magnitude higher efficiency than existing techniques. This dramatically reduces the required measurement time for computed phase tomography and opens up the way for three-dimensional investigations of previously inaccessible quantum-mechanical phase interactions of neutrons with matter.

Energy-selective neutron transmission imaging at a pulsed source

Abstract: Energy-selective neutron radiography experiments were carried out at the ISIS pulsed spallation source. This neutron transmission imaging technique combines the hardware used for conventional neutron radiography with the Bragg edge transmission features of time-of-flight methods. The main component of the energy-selective radiography set-up was a gated image-intensified CCD camera that viewed a neutron sensitive scintillation screen via a mirror. Energy resolution was obtained via synchronization of the light-intensifier with the pulse structure of the neutron source. It is demonstrated that contrast enhancement of materials can be straightforwardly achieved, and that microstructural features in metal samples can be directly visualized with high spatial resolution by taking advantage of the Bragg edges in the energy dependent neutron cross sections.

The micro-setup for neutron imaging: A major step forward to improve the spatial resolution

Abstract: To overcome present limitations of the spatial resolution in neutron imaging a newly designed setup was realized at the ICON facility [G. Kuhne et al., ICON—the new facility for cold neutron imaging at the Swiss spallation neutron source SINQ, Swiss Neutron News 28 (December 2005), pp. 20–29, 〈 http://sgn.web.psi.ch/sgn/snn/snn_28.pdf 〉], which is installed at the cold neutron beam line 52 at the Swiss spallation neutron source SINQ [G.S. Bauer, Nucl. Instr. and Meth. A 463 (2001) 505] since 2005. It was found by dedicated performance measurements, that the inherent spatial resolution of this locally fixed neutron imaging device is better than 50 μm, corresponding to 20 line pairs/mm in spatial frequency at 10% of the modulation transfer function (MTF). Therefore, the system has the potential to perform neutron tomography investigations with a resolution better than that previously achieved. This article describes the design features, details of the installation and the results from first test measurements. It gives an outlook for the further potential of this technique in both radiography and tomography applications.

The Direct Sampling method to perform multiple‐point geostatistical simulations

Abstract: [1] Multiple-point geostatistics is a general statistical framework to model spatial fields displaying a wide range of complex structures. In particular, it allows controlling connectivity patterns that have a critical importance for groundwater flow and transport problems. This approach involves considering data events (spatial arrangements of values) derived from a training image (TI). All data events found in the TI are usually stored in a database, which is used to retrieve conditional probabilities for the simulation. Instead, we propose to sample directly the training image for a given data event, making the database unnecessary. Our method is statistically equivalent to previous implementations, but in addition it allows extending the application of multiple-point geostatistics to continuous variables and to multivariate problems. The method can be used for the simulation of geological heterogeneity, accounting or not for indirect observations such as geophysics. We show its applicability in the presence of complex features, nonlinear relationships between variables, and with various cases of nonstationarity. Computationally, it is fast, easy to parallelize, parsimonious in memory needs, and straightforward to implement.

Coherent methods in the X-ray sciences

Abstract: X-ray sources are developing rapidly and their coherent output is growing correspondingly. The increased coherent flux from modern X-ray sources is being matched with an associated development in experimental methods. This article reviews the literature describing the ideas that utilize the increased brilliance from modern X-ray sources. It explores how ideas in coherent X-ray science are leading to developments in other areas, and vice versa. The article describes measurements of coherence properties and uses this discussion as a base from which to describe partially coherent diffraction and X-ray phase-contrast imaging, with applications in materials science, engineering and medicine. Coherent diffraction imaging methods are reviewed along with associated experiments in materials science. Proposals for experiments to be performed with the new X-ray free-electron lasers are briefly discussed. The literature on X-ray photon-correlation spectroscopy is described and the features it has in common with other coherent X-ray methods are identified. Many of the ideas used in the coherent X-ray literature have their origins in the optical and electron communities and these connections are explored. A review of the areas in which ideas from coherent X-ray methods are contributing to methods for the neutron, electron and optical communities is presented.

A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

Abstract: aLawrence Berkeley National Laboratory, Berkeley, California 94720, USA bLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USA cUnited Technologies Research Center, East Hartford, Connecticut 06118, USA dSchool of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom eChemical and Biomolecular Engineering Department, University of California, Berkeley, California 94720, USA fFuel Cell Research and Development, General Motors, Pontiac, Michigan 48340, USA gBallard Power Systems, Burnaby, British Columbia V5J 5J8, Canada hFuel Cell Research Centre, Queens University, Kingston, Ontario K7L 3N6, Canada iDepartment of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA jDepartment of Mechanical Aerospace and Biomedical Engineering, University of Tennessee at Knoxville, Knoxville, Tennessee 37996, USA kDepartment of Mechanical Engineering Technology, SUNY Alfred State College, Alfred, New York 14802, USA lDepartment of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G, Canada