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Understanding surface chemistry and the properties of layers and buried interfaces is a key challenge in life science and soft matter research. Examples include biological membranes, drug delivery systems, cosmetics and food. Neutron reflectometry is well suited to probing interface systems, and FREIA is a reflectometer optimised for soft condensed matter and life sciences. Both the structure and kinetics in thin film samples are of interest, particularly during their formation and in response to environmental changes. FREIA will allow experiments to be carried out without moving the sample, meaning that fast simultaneous measurements can be made over a very broad structural range to follow dynamic processes, such as chemical reactions, deposition of coatings and encapsulation/release from smart materials.
The challenges to be met in soft condensed matter and the life sciences are as wide ranging as the topics investigated. These include, but are not limited to:
Time-of-flight (tof) neutron reflectometry offers the possibility to record a range of Q-values simultaneously, allowing determination of both structure and chemical composition as a function of time. The key challenge lies in matching the time-resolution and the dynamic Q-range of the measurements to the time scales of the structural changes investigated. The key scientific drivers for FREIA are to allow fast kinetic measurements with the broadest possible simultaneous Q-range, and to provide high-throughput measurements across the scientific scope.
The instrument views the upper cold moderator and consists of a single elliptical guide, which is inclined at 2° below the x-axis and has its first vertical focal point in the cold moderator.
The guide has elliptical top/bottom faces while the horizontal guide with is constant at 4cm. The first 13m of the elliptical guide encloses a horizontal S-bender with 3 channels (m=3.2) and 130m radius of curvature. The elliptical guide and has a variable m-coating on the top and bottom faces varying from m=6 at the start/end to m=3 in the middle and back. The elliptical guide ends at 20m, and is followed by a 15cm gap for a solid-state silicon S-bender (upgrade option) for polarizing the beam, the collimation section. The 2m collimation section consists of interchangeable 3 guide sections, each designed to work with the polarized beam upgrade option:
The detector, designed in-house at ESS is located at a fixed distance of 3 m from the sample and has 0.5 mm x 2.5 mm resolution on the 250 mm x 250 mm area.
The instrument proposal described the instrument performance with the TDR moderator in terms of a series of virtual experiments that were benchmarked against experimental data from FIGARO at ILL.
In terms of measurement times, the gain factor for the TDR moderator was ~25. Since the proposal, the ESS moderator upgrade and optimization of the bender configuration change have resulted in an additional gain factor of 3.5 over this, making the full gain factor 80 for 5MW operations. This is applicable for all of the FREIA operating modes relative to like-for-like conditions on existing instruments. At 2MW, FREIA can therefore be expected to perform with a gain factor of approximately 30.
The guide geometry of FREIA enables the fast kinetics mode without moving the sample or detector in a manner that is not available on any existing instrument.
The extremely fast measurements possible on FREIA will enable both kinetic and large parametric studies of complex systems not accessible with neutrons today and will also increase the experimental throughput by at least an order of magnitude.