Design of a compact electron accelerator-driven pulsed neutron facility at AIST

Abstract We have designed and been constructing a compact accelerator-driven neutron facility for Bragg edge transmission imaging of structural materials to obtain position dependent crystallographic information. In order to combine a high neutron wavelength resolution, which is especially required for strain measurements, and an intense neutron beam flux at the sample position, which is required for obtaining high quality statistics within practical measurement times, the components of the neutron facility are optimized. To achieve a high wavelength resolution while maintaining an intense neutron beam flux at the sample position, a solid methane decoupled cold moderator at about 20 K coupled with neutron guide tubes is employed. The target–moderator system, especially the moderator thickness was optimized using the Monte-Carlo simulation code PHITS. Neutrons will be produced using a 35-MeV electron accelerator which is currently under construction. The accelerator has a design maximum beam power of 10 kW, a maximum repetition rate of 100 Hz and a maximum pulse width of 10 μ s . The combination of the flight path length of about 8 m and the repetition rate is suitable for efficient Bragg edge measurements. The pulse width of the electron beam is suitable to achieve a high wavelength resolution with the solid methane decoupled moderator. The estimated flux of the neutron beam at the sample position is 1.2 × 10 4 ∼ 4 . 5 × 10 4 /cm 2 /s depending on the usage of super mirror guide tubes. The wavelength resolution at the sample is 0.5 ∼ 0.7% in the wavelength region from 0.3 to 0.4 nm.