Monte-Carlo simulations of small angle neutron scattering instruments at European spallation source

Abstract

Monte-Carlo simulations of small angle neutron scattering (SANS) instruments have been performed using the VITESS software package in order to investigate the performance of such neutron spectrometers at high-power spallation sources as European spallation source (ESS). The performed simulations show that a low Q-range SANS instrument down to Q = 3 × 1 0 - 4 Å - 1 can be suitably built using a 60 m free neutron flight path (30 m collimation length and 30 m sample to detector distance) and a wavelength range up to 20 Å. Free neutron flight paths of 30 and 4 m with wavelength ranges of 4.6–6.5 and of 4.6–10 Å cover accessible Q-ranges of 2×10 −3–6×10 −2 and 2×10 −2–0.45 Å −1, respectively, with fair resolution and large overlap regions. The total length of the instrument would be 66 m from source to detector. Instruments with significantly larger neutron flight paths show no further gain in its performance. Highest count rates were received at the proposed long pulse target station of ESS with up to an order of magnitude intensity gain compared to the proposed short pulse target station of ESS or the ILL as neutron source in the three wavelength ranges anticipated.