A sample environment defines the container + components used to hold a sample during a run. This page details the process of a sample environment within Mantid.
A sample environment is defined by:
At a minimum a sample environment is expected to define a container with both its geometry and composition.
An environment definition is contained within a file using XML syntax. A minimal structure with a single container would have the following form:
<!-- Filename: CRYO-01.xml -->
<environmentspec>
<materials>
<material id="vanadium" formula="V"/>
</materials>
<components>
<containers>
<container id="10mm" material="vanadium">
<geometry>
<!-- geometry of container -->
</geometry>
<samplegeometry>
<!-- geometry of sample -->
</samplegeometry>
</container>
</containers>
</components>
</environmentspec>
The geometry of both the sample and container are defined using the same syntax used in the instrument definition files to define detector shapes. See here for detail on defining shapes in XML.
Multiple containers container be specified in the definition. The correct container for a run must be chosen by the user at the time the environment is attached to a workspace with the Environment option on the SetSample algorithm.
Each component is assigned a material, which defines properties such as the number density and neutron scattering cross sections, amongst other things. All materials defined for an environment must be defined within the <materials> tags and each material must have a unique id within the file. The id is used to reference the material when defining a container or component.
The other attributes define the properties of the material. The allowed attributes map to the arguments of a similar name on the SetSampleMaterial algorithm
A given setup may have other components within the beam that must be included. These container be included using the component tag rather than the container tag. For example, a heat shield container be added to the above definition like so:
<!-- Filename: CRYO-01.xml -->
<environmentspec>
<materials>
<material id="vanadium" formula="V"/>
<material id="aluminium" formula="Al"/>
</materials>
<components>
<containers>
<container id="10mm" material="vanadium">
<geometry>
<!-- geometry of container -->
</geometry>
<samplegeometry>
<!-- geometry of sample -->
</samplegeometry>
</container>
</containers>
<component id="heat-shield" material="aluminium">
<geometry>
<!-- geometry of sheild-->
</geometry>
</component>
</components>
</environmentspec>
A new material, aluminium has been added to the materials list and the heat shield is defined as an arbitrary component. The component tag behaves in a similar fashion to the container tag with the exception that it container not contain a samplegeometry.