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4SEASONS is a Fermi chopper spectrometer in operation at the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). 4SEASONS is expected to facilitate highefficiency measurements of weak inelastic signals on novel spin and lattice dynamics using thermal neutrons. The spectrometer is equipped with a coupled moderator and sophisticated components such as an elliptical converging neutron guide with high-critical-angle supermirrors, long (2.5 m) position-sensitive detectors, and a Fermi chopper appropriate for multiple-incident-energy (multi-E i ) measurements by the repetition-rate multiplication technique. Herein, we discuss in detail the design and performance of the spectrometer, and present some examples of the measurements obtained using this spectrometer.

Structural characterization of interfaces composed of soft materials (soft interfaces) helps in understanding their physical behavior. Neutron reflectometry is one of the most powerful tools to characterize interfacial structures with spatial resolution in nanometers. We have installed a novel horizontal-type time-of-flight neutron reflectometer SOFIA (SOFt Interface Analyzer) at the Japan Proton Accelerator Research Complex. The instrument is capable of accepting two downward neutron beams, at 2.21 and 5.71 to horizontal, which dedicate neutron reflectivity (NR) measurements over a wide range of neutron momentum transfer q (q ¼ (4p/k)sinh, where k and h are wavelength and incident angle, respectively). The accuracy of NR up to q ¼ 6 nm À1 was confirmed by measuring deuterated polystyrene (d-PS) thin films on a silicon (Si) wafer and multilayers of cadmium stearate prepared by the Langmuir-Blodgett method. NR at the deuterium oxide (D 2 O)/Si disk showed specular reflection down to 10 À6-10 À7 and q up to 2.0 nm À1 along the perpendicular to the sample surface, which improved the precise analysis of swollen polyelectrolyte brush structure at the D 2 O interface. Then, time-resolved in-situ NR measurements were carried out at 1-min intervals to observe interfacial mixing of d-PS on the PS brush surface during 398 K annealing, demonstrating that nonequilibrium behavior at the interfaces can be analyzed on the order of minutes.

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