Small Angle Neutron Scattering (SANS) and Reflectometry at the European Spallation Source
Small Angle Neutron Scattering (SANS)
Small Angle Neutron Scattering (SANS) is one of most heavily used method with respect to both, total number of users as well as the variety of scientific areas. SANS instruments are the flagships at neutron sources. They allow to measure structures on the nanometer scale. Their large importance in material science, soft matter, biology and life sciences relates to the special contrasts available with neutrons. In particular H/D replacement in organic substances and magnetic scattering in hard matter allow unique insights.
An instrument concept which ideally exploits the pulse structure at the ESS allows to access a large dynamical range of length scales, which at a continuous reactor source would require several instrument set-ups.
For the planned time-of-flight mode of a SANS machine at the ESS conventional instrument concepts have to be adapted to the neutron pulse structure in particular with respect to the broad wavelength band at the ESS. Significant development work has still to be done on broadband polarization and polarization analysis. Concepts to cope with the fast λ-variation of the resolution have to be found. Finally, the potential of focusing concepts to largely extend resolution or improve flux at the sample shall be investigated. Latter will allow to reach the micrometer range or to measure small samples at reduced Q-resolution.
The work on a innovative SANS instrument at the ESS encompassing the design of neutron optics for a fast change of collimation condition in the sub-second time interval and a concept for a small sample instrument is done in collaboration with the Helmholtz centers in Berlin and Geesthacht.
Reflectometry is a powerful tool to investigate magnetic layer structures or adsorbed films on surfaces of liquids and solids. Operated in the time-of-flight mode, reflectometer are well adapted to the properties of a long pulse spallation source. The very high intensity of the neutron pulses at the ESS will allow to deal with new challenges in this area of science.
However, to optimize the use of reflectometry at the ESS development work has to be done. This relates in particular to question how to exploit the long, intense neutron pulses having at the same time a variable Q-resolution. Furthermore, concepts for the non- specular scattering and the grazing-incidence option have to be worked out.
Based on the moderator spectrum by means of simulation questions like moderator-instrument distance, neutron transport and focusing, polarization and polarization analysis, pulse shaping and spin echo encoding are addressed.
The work on reflectometry at the ESS is done in collaboration with the Helmholtz centers in Berlin and Geesthacht.