Monte Carlo simulations of the S-shaped neutron guides with asymmetric concave and convex surface coatings

Abstract

During the last decades, neutron beam transportation has been a well-known and established subject of designing proper neutron guides. However, sometimes unusual adaptation or adjustments are required out of original projects and after the operation beginning of facilities. An inter-center transfer of instrument locations also requires a new approach that is not described in detail in the literature. Inside these situations, the use of S-shaped guides has not been fully discussed in the literature. From a geometrical analysis, we have developed a construction formalism of a minimal S-shaped guide by only considering the exclusion of the Line-of-Sight. The guide model has been studied through the wavelength cutoff and the neutron transport efficiency analysis. Here, Monte Carlo simulations using MCSTAS software have been applied. By intending to optimize these guide systems, simulations of this study also consider scenarios that have different supermirrors. A formalism to determine wavelength cutoff for unique and variable index guide systems has also been developed. There is a good correspondence between the theoretical cutoff wavelength values and the corresponding values obtained through Monte Carlo simulations. In addition, we have found specific configurations that combine efficient neutron transport and lower m-values on the convex surfaces of curved guides that form the S-shaped guide.