arXiv subjects

R. Gaehler

Publications and source records attributed to R. Gaehler.

5 recordsLinked to original sources

arXiv2006

Imaging with Scattered Neutrons

We describe a novel experimental technique for neutron imaging with scattered neutrons. These scattered neutrons are of interest for condensed matter physics, because they permit to reveal the local distribution of incoherent and coherent scattering within a sample. In contrast to standard attenuation based imaging, scattered neutron imaging distinguishes between the scattering cross section and the total attenuation cross section including absorption. First successful low-noise millimeter-resolution images by scattered neutron radiography and tomography are presented.

nucl-ex↗

arXiv2006

Neutron Radiography Analysis of a Transient Liquid Phase Joint

Neutron radiography in many cases is the only non-destructive technique available for the analysis of a wide range of samples from metallurgy, materials engineering and materials testing. In this paper the potential of the technique is illustrated for a transient liquid phase (TLP) joint. TLP bonding produces interface free and stress free joints. The quality and properties of the joint depend on the diffusion of an interlayer into the base material. A TLP joint is visualised and the diffusion profile of the boron contained in the bonding additives is determined. Parameters of the bonding process are determined quantitatively from this profile, and flaws in the joint are detected.

cond-mat.mtrl-sci↗

arXiv2005

A time lens for high resolution neutron time of flight spectrometers

We examine in analytic and numeric ways the imaging effects of temporal neutron lenses created by traveling magnetic fields. For fields of parabolic shape we derive the imaging equations, investigate the time-magnification, the evolution of the phase space element, the gain factor and the effect of finite beam size. The main aberration effects are calculated numerically. The system is technologically feasible and should convert neutron time of flight instruments from pinhole- to imaging configuration in time, thus enhancing intensity and/or time resolution. New fields of application for high resolution spectrometry may be opened.

cond-mat.other↗

arXiv2000

Comment on "Giant absorption cross section of ultracold neutrons in Gadolinium"

Rauch et al (PRL 83, 4955, 1999) have compared their measurements of the Gd cross section for Ultra-cold neutrons with an exptrapolation of the cross section for thermal neutrons and interpreted the discrepancy in terms of coherence properties of the neutron. We show the extrapolation used is based on a misunderstanding and that coherence properties play no role in absorption.

quant-ph↗

arXiv1997

Space-Time Approach to Scattering from Many Body Systems

We present scattering from many body systems in a new light. In place of the usual van Hove treatment, (applicable to a wide range of scattering processes using both photons and massive particles) based on plane waves, we calculate the scattering amplitude as a space-time integral over the scattering sample for an incident wave characterized by its correlation function which results from the shaping of the wave field by the apparatus. Instrument resolution effects - seen as due to the loss of correlation caused by the path differences in the different arms of the instrument are automatically included and analytic forms of the resolution function for different instruments are obtained. The intersection of the moving correlation volumes (those regions where the correlation functions are significant) associated with the different elements of the apparatus determines the maximum correlation lengths (times) that can be observed in a sample, and hence, the momentum (energy) resolution of the measurement. This geometrical picture of moving correlation volumes derived by our technique shows how the interaction of the scatterer with the wave field shaped by the apparatus proceeds in space and time. Matching of the correlation volumes so as to maximize the intersection region yields a transparent, graphical method of instrument design. PACS: 03.65.Nk, 3.80 +r, 03.75, 61.12.B

physics.optics↗