The Union components are a set of McXtrace components, originally developed for McStas by Mads Bertelsen [Ber17; BJL17] and subsequently ported to McXtrace, that take a fundamentally different approach to sample and sample-environment simulation than ordinary McXtrace components. This chapter explains the concepts behind the Union components and how to use them from an instrument file; the full parameter reference for every individual Union component is auto-generated from the component headers and found in the Component Manual’s Union chapter.
The McXtrace port covers the core of the framework – processes, materials, geometries, masks, exit volumes and the master component – but not (yet) every feature of the McStas original: there is currently no logger, absorption-logger, conditional or surface (reflection/refraction) support, and no ray-history tagging system. Everything described in this chapter is available; where a feature exists in McStas but not McXtrace, this is noted explicitly.