# 3.3.2.13. NXsas¶

Status:

application definition, extends NXobject

Description:

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:

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.

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

name: (optional) NX_CHAR

probe: (required) NX_CHAR

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.

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 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 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 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 (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 data.

Obligatory value: data