Progress in High Resolution Chopper Spectrometer HRC by improving collimator and Fermi chopper

The High Resolution Chopper Spectrometer (HRC) is installed at the Japan Proton Accelerator Research Complex (J-PARC) and is utilized for a wide range of dynamical studies of materials over a wide energy-momentum space with high resolution. Neutron Brillouin scattering (NBS), i.e., inelastic neutron scattering close to the forward direction, can be performed with the HRC, because this instrument utilizes low angle detectors and high-energy neutrons which facilitates a high resolution. Since the solid angle of the detection area for NBS experiments is limited to very low scattering angles, improvements of the HRC are required to increase the neutron flux with reducing the background. Given the success of the HRC for NBS studies, the neutron intensities for NBS experiments have been improved by changing the detector layout, reducing deformation of the slit package during rotation of the Fermi chopper, and fabricating a longer collimator. At present, we have made further improvements. At around the incident neutron energy Ei = 100 meV, the neutron flux was significantly increased for an energy resolution of ΔE∕Ei = 2%, and the best energy resolution achieved was nearly 1% resolution with an acceptable neutron flux.