User and Programmers Guide to the Neutron Ray-Tracing Package McStas, version 3.9

6  The Union components

The Union components are a set of McStas components, originally developed by Mads Bertelsen [Ber17; BJL17], that take a fundamentally different approach to sample and sample-environment simulation than ordinary McStas 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.

6.1 Motivation
6.1.1 Volumes, priority and overlap
6.2 Component classes
6.2.1 Loading the Union library
6.2.2 Scattering processes
6.2.3 Union_make_material
6.2.4 Geometry components
6.2.5 Union_master
6.2.6 Surfaces
6.2.7 Logger components
6.2.8 Conditional components
6.2.9 Tagging: ray histories
6.3 The propagation algorithm
6.3.1 Basic Monte Carlo step
6.3.2 Intersection and destination lists
6.3.3 Known limitations
6.4 A complete example
6.5 Further examples and worked tutorials