3.3.2.13. NXsas

Status:

application definition, extends NXobject

Description:

Raw, monochromatic 2-D SAS data with an area detector. ...

Raw, monochromatic 2-D SAS data with an area detector.

This is an application definition for raw data (not processed or reduced data) from a 2-D small angle scattering instrument collected with a monochromatic beam and an area detector. It is meant to be suitable both for neutron SANS and X-ray SAXS data.

It covers all raw data from any monochromatic SAS techniques that use an area detector: SAS, WSAS, grazing incidence, GISAS

It covers all raw data from any SAS techniques that use an area detector and a monochromatic beam.

Symbols:

The symbol(s) listed here will be used below to coordinate fields with the same shape.

nXPixel: Number of pixels in x direction.

nYPixel: Number of pixels in y direction.

Groups cited:

NXcollimator, NXdata, NXdetector, NXentry, NXgeometry, NXinstrument, NXmonitor, NXmonochromator, NXsample, NXshape, NXsource

Structure:

ENTRY: (required) NXentry

title: (optional) NX_CHAR ⤆

start_time: (optional) NX_DATE_TIME ⤆

end_time: (optional) NX_DATE_TIME ⤆

definition: (required) NX_CHAR ⤆

Official NeXus NXDL schema to which this file conforms. ...

Official NeXus NXDL schema to which this file conforms.

Obligatory value: NXsas

INSTRUMENT: (required) NXinstrument ⤆

name: (required) NX_CHAR ⤆

Name of the instrument actually used to perform the experiment.

SOURCE: (required) NXsource ⤆

type: (required) NX_CHAR ⤆

Type of radiation source.

name: (optional) NX_CHAR ⤆

Name of the radiation source.

probe: (required) NX_CHAR ⤆

Name of radiation probe, necessary to compute the sample contrast. ...

Name of radiation probe, necessary to compute the sample contrast.

Any of these values: neutron | x-ray

MONOCHROMATOR: (required) NXmonochromator ⤆

wavelength: (required) NX_FLOAT {units=NX_WAVELENGTH} ⤆

The wavelength (\(\lambda\)) of the radiation.

wavelength_spread: (optional) NX_FLOAT

delta_lambda/lambda (:math:`\Delta\lambda/\lambda`): ...

delta_lambda/lambda (\(\Delta\lambda/\lambda\)): Important for resolution calculations.

COLLIMATOR: (optional) NXcollimator ⤆

GEOMETRY: (required) NXgeometry ⤆

SHAPE: (required) NXshape ⤆

shape: (required) NX_CHAR ⤆

Any of these values: nxcylinder | nxbox

size: (required) NX_FLOAT {units=NX_LENGTH} ⤆

The collimation length.

DETECTOR: (required) NXdetector ⤆

data: (required) NX_NUMBER (Rank: 2, Dimensions: [nXPixel, nYPixel]) ⤆

This is area detector data, number of x-pixel versus ...

This is area detector data, number of x-pixel versus number of y-pixels.

Since the beam center is to be determined as a step of data reduction, it is not necessary to document or assume the position of the beam center in acquired data.

It is necessary to define which are the x and y directions, to coordinate with the pixel size and compute Q.

distance: (required) NX_FLOAT {units=NX_LENGTH} ⤆

The distance between detector and sample.

x_pixel_size: (required) NX_FLOAT {units=NX_LENGTH} ⤆

Physical size of a pixel in x-direction.

y_pixel_size: (required) NX_FLOAT {units=NX_LENGTH} ⤆

Physical size of a pixel in y-direction.

polar_angle: (optional) NX_FLOAT {units=NX_ANGLE} ⤆

azimuthal_angle: (optional) NX_FLOAT {units=NX_ANGLE} ⤆

rotation_angle: (optional) NX_FLOAT {units=NX_ANGLE}

aequatorial_angle: (optional) NX_FLOAT {units=NX_ANGLE}

beam_center_x: (optional) NX_FLOAT {units=NX_LENGTH} ⤆

This is the x position where the direct beam would hit the detector. ...

This is the x position where the direct beam would hit the detector. This is a length, not a pixel position, and can be outside of the actual detector.

It is expected that data reduction will determine beam center from the raw data, thus it is not required here. The instrument can provide an initial or nominal value to advise data reduction.

beam_center_y: (optional) NX_FLOAT {units=NX_LENGTH} ⤆

This is the y position where the direct beam would hit the detector. ...

This is the y position where the direct beam would hit the detector. This is a length, not a pixel position, and can be outside of the actual detector.

It is expected that data reduction will determine beam center from the raw data, thus it is not required here. The instrument can provide an initial or nominal value to advise data reduction.

SAMPLE: (optional) NXsample ⤆

name: (required) NX_CHAR ⤆

Descriptive name of sample.

aequatorial_angle: (optional) NX_FLOAT {units=NX_ANGLE}

MONITOR: (optional) NXmonitor ⤆

mode: (required) NX_CHAR ⤆

Count to a preset value based on either clock time ...

Count to a preset value based on either clock time (timer) or received monitor counts (monitor).

Any of these values: monitor | timer

preset: (required) NX_FLOAT

Preset value for time or monitor.

integral: (required) NX_FLOAT {units=NX_ANY}

Total integral monitor counts.

DATA: (required) NXdata ⤆

@signal: (optional) NX_CHAR ⤆

Name the *plottable* field. The link here defines this name as ...

Name the plottable field. The link here defines this name as data.

Obligatory value: data

data: link (suggested target: /NXentry/NXinstrument/NXdetector/data)

Hypertext Anchors

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

NXDL Source:

https://github.com/nexusformat/definitions/blob/main/applications/NXsas.nxdl.xml