Design and validation of a neutron double crystal monochromator for ICON

Abstract

Many applications using neutron imaging for materials science use diffraction-based contrast to explore and understand the condition of the samples. Diffraction-based methods require wavelength resolution. The neutron imaging instrument ICON at Paul Scherrer Institut has, until recently, only provided this functionality using a velocity selector. We designed a new double crystal monochromator (DCM) for the conditions at ICON as an option to meet the wavelength resolution demands of specific advanced methods such as diffraction contrast neutron imaging. The DCM can also be combined with the velocity selector. The device uses two pyrolitic graphite crystals as active components, allowing the selection of wavelengths in the interval 2–6 Å. This wavelength interval covers the main applications for wavelength-selective imaging considered at ICON. The device is designed for installation near the instrument shutter system. This position has the advantage that the effective field of view is maximized at the experiment position due to the beam divergence of the ICON. On the other hand, this position means that the beam displacement relative to the initial beam is relatively short. Thus, shielding is vital for the installation. We describe the device design and show the results from the first characterization experiments.