Pulsed neutron-beam flux with the supermirror neutron guide system at AISTANS

Neutron-beam flux spectra at the compact electron accelerator-driven pulsed neutron facility AISTANS were measured at a detector position of 8 m from the neutron source. Based on the measured spectra, the characteristics of the neutron beam from the decoupled ~ 20 K solid methane moderator and the amplification of the neutron-beam flux at the detector position when supermirror guide tubes are installed in the beamline between the moderator and detector position were analyzed. A neutron spectral temperature of 32.6 K was observed, suggesting a physical temperature for the moderator of roughly 26 K with an electron beam power on a neutron production target of ~ 1 kW. Furthermore, the absolute intensity of the measurement spectrum was of the same order (approximately 2/3) as that of the simulation calculation. The geometrical neutron path and neutron phase space through the supermirror guide tubes were investigated diagrammatically to find the relationship between the neutron reflection position and wavelength and measured imaging quality. The increase in neutron flux at the detector when supermirror guide tubes are used was measured experimentally, and the results showed reasonable agreements with those of the simulation calculations. This amplification factor reached a value of approximately 6 at a wavelength of around 0.4 nm and approximately 8 for the long neutron wavelength exceeding 0.7 nm.