base class, extends NXobject


A neutron optical element to direct the path of the beam.

NXguide is used by neutron instruments to describe a guide consists of several mirrors building a shape through which neutrons can be guided or directed. The simplest such form is box shaped although elliptical guides are gaining in popularity. The individual parts of a guide usually have common characteristics but there are cases where they are different. For example, a neutron guide might consist of 2 or 4 coated walls or a supermirror bender with multiple, coated vanes.

To describe polarizing supermirrors such as used in neutron reflection, it may be necessary to revise this definition of NXguide to include NXpolarizer and/or NXmirror.

When even greater complexity exists in the definition of what constitutes a guide, it has been suggested that NXguide be redefined as a NXcollection of NXmirror each having their own NXgeometry describing their location(s).

For the more general case when describing mirrors, consider using NXmirror.

NOTE: The NeXus International Advisory Committee welcomes comments for revision and improvement of this definition of NXguide.


nsurf: number of reflecting surfaces

nwl: number of wavelengths

Groups cited:

NXdata, NXgeometry, NXoff_geometry, NXtransformations


@default: (optional) NX_CHAR

Declares which child group contains a path leading to a NXdata group.

It is recommended (as of NIAC2014) to use this attribute to help define the path to the default dataset to be plotted. See https://www.nexusformat.org/2014_How_to_find_default_data.html for a summary of the discussion.

description: (optional) NX_CHAR

A description of this particular instance of NXguide.

incident_angle: (optional) NX_FLOAT {units=NX_ANGLE}

TODO: documentation needed

bend_angle_x: (optional) NX_FLOAT {units=NX_ANGLE}

TODO: documentation needed

bend_angle_y: (optional) NX_FLOAT {units=NX_ANGLE}

TODO: documentation needed

interior_atmosphere: (optional) NX_CHAR

Any of these values: vacuum | helium | argon

external_material: (optional) NX_CHAR

external material outside substrate

m_value: (optional) NX_FLOAT (Rank: 1, Dimensions: [nsurf])

The m value for a supermirror, which defines the supermirror regime in multiples of the critical angle of Nickel.

substrate_material: (optional) NX_FLOAT (Rank: 1, Dimensions: [nsurf])

TODO: documentation needed

substrate_thickness: (optional) NX_FLOAT (Rank: 1, Dimensions: [nsurf]) {units=NX_LENGTH}

TODO: documentation needed

coating_material: (optional) NX_FLOAT (Rank: 1, Dimensions: [nsurf])

TODO: documentation needed

substrate_roughness: (optional) NX_FLOAT (Rank: 1, Dimensions: [nsurf]) {units=NX_LENGTH}

TODO: documentation needed

coating_roughness: (optional) NX_FLOAT (Rank: 1, Dimensions: [nsurf]) {units=NX_LENGTH}

TODO: documentation needed

number_sections: (optional) NX_INT {units=NX_UNITLESS}

number of substrate sections (also called nsurf as an index in the NXguide specification)

depends_on: (optional) NX_CHAR

NeXus positions components by applying a set of translations and rotations to apply to the component starting from 0, 0, 0. The order of these operations is critical and forms what NeXus calls a dependency chain. The depends_on field defines the path to the top most operation of the dependency chain or the string “.” if located in the origin. Usually these operations are stored in a NXtransformations group. But NeXus allows them to be stored anywhere.

The entry opening of the guide lies on the reference plane. The center of the opening on that plane is the reference point on the x and y axis. The reference plane is orthogonal to the z axis and is the reference point along the z axis. Given no bend in the guide, it is parallel with z axis and extends in the positive direction of the z axis.


GEOMETRY: (optional) NXgeometry

DEPRECATED: Use the field depends_on and NXtransformations to position the guid and NXoff_geometry to describe its shape instead

TODO: Explain what this NXgeometry group means. What is intended here?

reflectivity: (optional) NXdata

Reflectivity as function of reflecting surface and wavelength

@signal: (optional) NX_CHAR

Obligatory value: data

@axes: (optional) NX_CHAR

Obligatory value: surface wavelength

@surface_indices: (optional) NX_CHAR

Obligatory value: 0

@wavelength_indices: (optional) NX_CHAR

Obligatory value: 1

data: (optional) NX_NUMBER (Rank: 2, Dimensions: [nsurf, nwl])

reflectivity of each surface as a function of wavelength

surface: (optional) NX_NUMBER (Rank: 1, Dimensions: [nsurf]) {units=NX_ANY}

List of surfaces. Probably best to use index numbers but the specification is very loose.

wavelength: (optional) NX_NUMBER (Rank: 1, Dimensions: [nwl]) {units=NX_WAVELENGTH}

wavelengths at which reflectivity was measured

OFF_GEOMETRY: (optional) NXoff_geometry

This group describes the shape of the beam line component

TRANSFORMATIONS: (optional) NXtransformations

This is the group recommended for holding the chain of translation and rotation operations necessary to position the component within the instrument. The dependency chain may however traverse similar groups in other component groups.

Hypertext Anchors

List of hypertext anchors for all groups, fields, attributes, and links defined in this class.

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