Redirect to released documentation

**Status**:

contributed definition, extendsNXobject, version 1.0

**Description**:

Implementation of the canSAS standard to store reduced multi-dimensional small-angle scattering data.

for more details, see:

**Symbols**:

No symbol table

**Groups cited**:*NXcollection*,*NXcollimator*,*NXdata*,*NXdetector*,*NXinstrument*,*NXorientation*,*NXparameters*,*NXprocess*,*NXsample*,*NXsource*,*NXsubentry*,*NXtranslation*

**Structure**:

(subentry):NXsubentryPlace the canSAS

SASentrygroup as a child of a NeXusNXentrygroup.Note: It is required for all numerical objects to provide a

unitsattribute that describes the engineering units. Use the Unidata UDunits [1] specification as this is compatible with various community standards.

[1] The UDunits specification also includes instructions for derived units.

@canSAS_class:NX_CHAROfficial canSAS group:

SASentryObligatory value:

SASentry

@version:NX_CHARDescribes the version of the canSAS standard used to write this data. This must be a text (not numerical) representation. Such as:

@version="1.0"Obligatory value:

1.0

definition:NX_CHAROfficial NeXus NXDL schema to which this subentry conforms.

Obligatory value:

NXcanSAS

title:NX_CHARTitle of thisSASentry.

run:NX_CHARRun identification for this

SASentry. For many facilities, this is an integer. Use multiple instances ofrunas needed.

@name:NX_CHAROptional string attribute to identify this particularrun. Could use this to associate (correlate) multipleSASdataelements withrunelements.

(data):NXdataA

SASDatagroup contains reduced a single small-angle scattering data set that can be represented as or .

Qcan be either a vector () or a vector magnitude ()The name of each

SASdatamust be unique within a SASentry group. Such assasdata01.A

SASdatagroup has several attributes:

- I_axes
- Q_indices
- Mask_indices
To indicate the dependency relationships of other varied parameters, use attributes similar to

@Mask_indices(such as@Temperature_indicesor@Pressure_indices).

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASdata

Obligatory value:

SASdata

@I_axes:NX_CHARComma-separated list that describes the names of the data objects that correspond to the indices of the

Idata object. Such as:@I_axes="Temperature,Time,Pressure,Q,Q"Since there are five items in the list, the intensity field

Imust be a five-dimensional array (rank=5).

@Q_indices:NX_CHARArray that describes which indices (of the data object) are used to reference the

Qdata object. The items in this array use zero-based indexing. Such as:@Q_indices=1,3,4which indicates that

Qrequires three indices from the data object: one for time and two for Q position. Thus, in this example, theQdata is time-dependent: .

@Mask_indices:NX_CHARArray that describes which indices (of the data object) are used to reference the

Maskdata object. The items in this array use zero-based indexing. Such as:@Mask_indices=3,4which indicates that Q requires two indices from the data object for Q position.

Q:NX_NUMBER{units=NX_PER_LENGTH}Array of data to accompany .

may be represented either as the three-dimensional scattering vector or by the magnitude of the scattering vector, .

When we write , we may refer to either or both of or , depending on the context.

@uncertainty:NX_CHARTypically the estimated standard deviation. More general, this is the estimate of the uncertainty of each “math:Q.

Can use this to describe the slit-length at each datum. Use a subgroup to describe any supplementary uncertainty data such as two-dimensional.

(optional for numerical arrays) Name of the data object (in this SASdata group) that provides the uncertainty to be used for data analysis.

I:NX_NUMBERArray of intensity () data.

The intensity may be represented in one of these forms:

absolute units: differential cross-section per unit volume per unit solid angle (typical units: 1/cm/sr)

absolute units: differential cross-section per unit atom per unit solid angle (typical units: cm^2)

arbitrary units: usually a ratio of two detectors but units are meaningless (typical units: a.u.)This presents a few problems for analysis software to sort out when reading the data. Fortunately, it is possible to analyze the

unitsto determine which type of intensity is being reported and make choices at the time the file is read. But this is an area for consideration and possible improvement.One problem arises with software that automatically converts data into some canonical units used by that software. The software should not convert units between these different types of intensity indiscriminately.

A second problem is that when arbitrary units are used, then the set of possible analytical results is restricted. With such units, no meaningful volume fraction or number density can be determined directly from .

In some cases, it is possible to apply a factor to convert the arbitrary units to an absolute scale. This should be considered as a possibility of the analysis process.

@uncertainty:NX_CHARTypically the estimated standard deviation. for Poisson statistics. More generally, though, this is the estimate of the uncertainty of each “math:I.

(optional for numerical arrays) Name of the data object (in this SASdata group) that provides the uncertainty to be used for data analysis.

Idevis the canonical name from the 1D standard. The multi-D standard allows for this name to be described in this attribute.

Qmean:NX_CHAR{units=NX_PER_LENGTH}Mean value of for this data point. Useful when describing data that has been binned from higher-resolution data. It is unexpected forQandQmeanto have different units.

ShadowFactor:NX_CHAR{units=NX_DIMENSIONLESS}A numerical factor applied to pixels affected by the beam stop penumbra. Used in data files from NIST/NCNR instruments.

See: J.G. Barker and J.S. Pedersen (1995)

J. Appl. Cryst.28, 105-114.

(parameters):NXparametersSupplementary Uncertainty Data

@canSAS_class:NX_CHARad hoc canSAS group: NXcanSAS (contributed definition); SASuncertainties

Obligatory value:

SASuncertainties

(instrument):NXinstrumentThis the SAS instrument.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASinstrument

Obligatory value:

SASinstrument

(collimator):NXcollimatorDescription of a collimating element in the instrument.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SAScollimation

Obligatory value:

SAScollimation

length:NX_NUMBER{units=NX_LENGTH}Amount/length of collimation inserted (as on a SANS instrument)

aperture:NXparametersDescription of a slit or aperture.

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

@name:NX_CHAROptional name attribute for this aperture

@type:NX_CHAROptional text attribute to describe the type of aperture (pinhole, 4-blade slit, Soller slit, ...).

distance:NX_NUMBER{units=NX_LENGTH}Distance from this collimation element to the sample.

size:NXparametersOpening dimensions of this aperture.

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

x:NX_NUMBER{units=NX_LENGTH}Dimension of the collimation in .

y:NX_NUMBER{units=NX_LENGTH}Dimension of the collimation in .

z:NX_NUMBER{units=NX_LENGTH}Dimension of the collimation in .

While is allowed by the canSAS standard, it may not make sense to use it in some situations. Use of may be ignored by processing software.

(detector):NXdetectorDescription of a detector in the instrument.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASdetector

Obligatory value:

SASdetector

name:NX_CHARIdentifies the name of this detector

SDD:NX_NUMBER{units=NX_LENGTH}Distance between sample and detector.

slit_length:NX_NUMBER{units=NX_PER_LENGTH}Slit length of the instrument for this detector, expressed in the same units as .

offset:NXparametersOffset of the detector position.

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

x:NX_NUMBER{units=NX_LENGTH}

y:NX_NUMBER{units=NX_LENGTH}

z:NX_NUMBER{units=NX_LENGTH}While is allowed by the canSAS standard, it may not make sense to use it in some situations. Use of may be ignored by processing software.

orientation:NXparametersThe orientation element describes simple rotations about a single axis (rather than a full set of rotations as in a crystallographic context).

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

roll:NX_NUMBER{units=NX_LENGTH}Roll is rotation about the axis.

pitch:NX_NUMBER{units=NX_LENGTH}Pitch is rotation about the axis.

yaw:NX_NUMBER{units=NX_LENGTH}Yaw is rotation about the axis.

beam_center:NXparametersPosition of the beam center on the detector

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

x:NX_NUMBER{units=NX_LENGTH}

y:NX_NUMBER{units=NX_LENGTH}

z:NX_NUMBER{units=NX_LENGTH}While is allowed by the canSAS standard, it may not make sense to use it in some situations. Use of may be ignored by processing software.

pixel_size:NXparameterssize of the pixels on this detector.

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

x:NX_NUMBER{units=NX_LENGTH}

y:NX_NUMBER{units=NX_LENGTH}

z:NX_NUMBER{units=NX_LENGTH}

(source):NXsourceDescription of the radiation source.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASsource

Obligatory value:

SASsource

radiation:NX_CHARName of the radiation used. Note that this is

notthe name of the facility!Any of these values:

Spallation Neutron SourcePulsed Reactor Neutron SourceReactor Neutron SourceSynchrotron X-ray SourcePulsed Muon SourceRotating Anode X-rayFixed Tube X-rayUV LaserFree-Electron LaserOptical LaserIon SourceUV Plasma Sourceneutronx-raymuonelectronultravioletvisible lightpositronproton

beam_shape:NX_CHARText description of the shape of the beam (incident on the sample).

wavelength:NX_NUMBER{units=NX_WAVELENGTH}wavelength () of radiation incident on the sample

wavelength_min:NX_NUMBER{units=NX_WAVELENGTH}Some facilities specify wavelength using a range. This is the lowest wavelength in such a range.

wavelength_max:NX_NUMBER{units=NX_WAVELENGTH}Some facilities specify wavelength using a range. This is the highest wavelength in such a range.

wavelength_spread:NX_NUMBER{units=NX_WAVELENGTH}Some facilities specify wavelength using a range. This is the width of such a range.

beam_size:NXparametersPhysical dimension of the beam (incident on the sample). If beam is round, just use .

@canSAS_class:NX_CHAR

ad hoccanSAS_class.Obligatory value:

container

x:NX_NUMBER{units=NX_LENGTH}

y:NX_NUMBER{units=NX_LENGTH}

z:NX_NUMBER{units=NX_LENGTH}

(sample):NXsampleDescription of the sample.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASsample

Obligatory value:

SASsample

ID:NX_CHARText string that identifies this sample.

thickness:NX_FLOAT{units=NX_LENGTH}Thickness of this sample

transmission:NX_NUMBER{units=NX_DIMENSIONLESS}Transmission () of this sample. Note that there is nounitsattribute as this number is dimensionless.

temperature:NX_NUMBER{units=NX_TEMPERATURE}Temperature of this sample.

details:NX_CHARAny additional sample details.

position:NXtranslationLocation of the sample in , , and .

orientation:NXorientationOrientation (rotation) of the sample.

(process):NXprocessDescription of a processing or analysis step.

Add additional fields as needed to describe value(s) of any variable, parameter, or term related to the

SASprocessstep. Be sure to includeunitsattributes for all numerical fields.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASprocess

Obligatory value:

SASprocess

name:NX_CHAROptional name for this data processing or analysis step

date:NX_DATE_TIMEOptional date for this data processing or analysis step. [2]

[2] (1, 2)ISO-8601 standard time representation.

Use a format for the date which is machine-readable such as ISO-8601 (e.g.,

yyyy-mm-ddThh:mm:ss) or modified ISO-8601 (e.g.,yyyy-mm-dd hh:mm:ss).See: http://www.w3.org/TR/NOTE-datetime or http://en.wikipedia.org/wiki/ISO_8601 for more details.

description:NX_CHAROptional description for this data processing or analysis step

term:NX_CHARSpecifies the value of a single variable, parameter, or term (while defined here as a string, it could be a number) related to the

SASprocessstep.The name

termis not required, it could take any name.

(collection):NXcollectionDescribes anything about

SASprocessthat is not already described.Any content not defined in the canSAS standard can be placed at this point.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASprocessnote

Obligatory value:

SASprocessnote

(collection):NXcollectionFree form description of anything not covered by other elements.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SASnote

Obligatory value:

SASnote

(data):NXdataThis describes certain data obtained from a variable-wavelength source such as pulsed-neutron source.

@canSAS_class:NX_CHAROfficial canSAS group: NXcanSAS (contributed definition); SAStransmission_spectrum

Obligatory value:

SAStransmission_spectrum

@name:NX_CHARIdentify what type of spectrum is being described. It is expected that this value will take either of these two values:

value meaning sample measurement with the sample and container can measurement with just the container

@timestamp:NX_DATE_TIMEISO-8601 time [2]

lambda:NX_NUMBER{units=NX_WAVELENGTH}Wavelength of the radiation.

T:NX_NUMBER{units=NX_DIMENSIONLESS}

**Source**:- Automatically generated from https://github.com/nexusformat/definitions/blob/master/contributed_definitions/NXcanSAS.nxdl.xml