Reflectometry Glossary

A

Alignment: The process of finding the position of an axis where it is centered/perpendicular to the neutron beam by scanning over a range of positions. This position is then usually defined as 0.

Diagram of axis conventions available here

Axis, X: Translation across the natural beam.

Axis, Y: Height relative to the natural beam.

Axis, Y: Displacement along the natural beam.

Axis, Chi: Yaw angle of a component relative to the natural beam. (Rotation in XZ Plane)

Axis, Phi: Pitch angle of a component relative to natural beam. (Rotation in YZ Plane)

Axis, Psi: Roll angle of a component relative to natural beam. (Rotation in XY Plane)

Axis, Long: Z Translation axis of disused INTER detector (pre tank upgrade)

Axis, Seesaw: Rotation of a bench around its centre, achieved by applying an equal but inverse height offset to its front and back height jacks. Used for bench alignment. Different to Bench Angle which rotates around the virtual sample point

B

Beam, Incoming: The source of the beam segment before interacting with a given a component as described by Y, Z and Angle coordinates. This is the outgoing beam of the last reflecting component the beam has interacted with, or the natural beam if no reflections apply.

Beam, Outgoing: The origin of the beam path segment after interacting with a given component. This becomes the incoming beam

Beam, Natural: The neutron beam as it enters an instrument blockhouse without any additional reflections. This is a downward 1.5° for TS1 beamlines and a downward 2.3° for TS2 beamlines. The natural beam defines the Z axis of the Y/Z tracking plane used by the reflectometry server, since axes get aligned to it i.e. an axis' position is redefined to 0 when it is centred on the natural beam.

Beam, Straight Through: See Natural Beam

Beam, Reflected: The current beam path including any reflections from mirrors & sample (often contrasted with the theoretical Natural Beam)

Beamline Object: The top level object holding & coordinating the whole geometry model inside the reflectometry server.

C

Component: An item on the beamline that interacts with the beam in some way (tracking or modifying its path)

Component, Passive: An item on the beamline which interacts with the beam but does not change the direction of the incoming beam e.g. slits

Component, Reflecting: An item on the beamline that can change the direction of the incoming beam for e.g. a super mirror

Configuration: Configuration in reflectometry defines the beamline and the components in the beamline. Reflectometry configuration is written in python.

D

Detector, Point (0D): A simple tube is used to integrate intensity, the detector itself has no position sensitivity, just the angle it is positioned at

Detector, Linear (1D): Also referred to as linear, area or multi-detector, where a stack of tubes/pixels is used to integrate intensity with either vertical or horizontal position sensitivity equal to the pixel size

Detector, Area (2D): Also referred to as area detector. Similar to the 1D but with both vertical and horizontal position sensitivity. Note pixels may not be uniform in horizontal/vertical size.

E

Engineering Correction: A correction that is added to setpoints / removed for readback values for a given axis at the Composite Driver level. These corrections can be of fixed value, or calculated by a user function or an interpolation matrix. These exist to account for slight inaccuracies in engineering, e.g. a mirror that is not perfectly flat.

I

Incident Angle: See Theta

M

Mirror: Some samples, such as liquids, cannot be angled. Mirrors can be used to change the incident angle of the beam to enable multiple angles to be measured from the surface, essentially angling the whole beamline around the sample instead rather than the other way around.

Mirror, Polarising: A mirror that additionally polarises the neutrons that it reflects.

Mirror, Super: Non-polarising mirror designed specifically for reflecting neutrons.

P

Parameter: A top-level user parameter, describing some value relative to the incoming beam. (aka. Beamline Parameter)

V

Virtual Sample Point: The theoretical intersection between the incoming beam at the sample and its movement axes.