SANSILLReduction v2¶

See Also¶

SANSILLMultiProcess, SANSILLIntegration

DarkCurrent¶

The dark current refers to the blocked beam measurement with cadmium or B4C. There is not much to do in this case, except time or monitor normalisation.

EmptyBeam¶

The empty beam measurement can be used for 2 purposes: beam center finding and flux calculation. It produces 2 outputs respectively. The main one is the time or monitor normalized empty beam measurement, which has sample logs BeamCenterX and BeamCenterY. Those are the coordinates of the calculated center-of-mass of the beam footprint. BeamRadius parameter is used as the radius of the circle where to search for it. This workspace itself is corrected for the beam center and the dark current can be subtracted if provided. One should be able to inspect by eye that at this stage the Z axis (i.e. the beam) passes through the center-of-mass of the signal. The second output is the integrated flux workspace which sums the intensities in a given radius around the Z after having corrected for the beam center. Here, TransmissionBeamRadius is used for the integration circle.

Transmission¶

Transmission calculation is a critical part of the reduction. Transmission refers to the central transmission value, which is calculated as the ratio of the integrated intensity transmitted through the sample and the empty beam flux. However, when applying the transmission correction, it is applied in a 2theta-dependent way, in order to account for flight path difference of the neutrons within the flat plate sample. For cylindrical samples, 2theta-dependence must be switched off. TransmissionBeamRadius governs the size of the circle to integrate the intensities within. Transmission runs can be concatenated, which can generate a single transmission workspace that can be later applied in a vectorized way. Of course, only transmissions measured at the same wavelength can be concatenated, as the transmission is wavelength dependent. Furthermore, the transmission runs are also allowed to be kinetic, in which case the transmissions will be calculated frame-by-frame, i.e. in a time-dependent fashion. Transmissions runs input can also have duplicated runs, in case the same transmission needs to be applied to more than one sample (see the dedicated section below). Transmission values must be positive and less than unity.

EmptyContainer¶

This is the container the samples are measured in. Empty container must be provided with its own transmission, which is typically close to 1, but still it is needed to perform the subtraction correctly. The container workspace is the first process type that is also normalized by the solid angle. This is just to allow the containers to be measured at different distances if needed. However, typically they are measured at the same beamline configurations as the samples.

Water¶

This refers to the incoherent isotropic standard sample, which is typically water, but can also be vanadium. This can be used for 2 purposes: correcting for relative inter-pixel detector efficiencies and, in case of water, calibrating the absolute scale. The water measurement can be used in 2 ways: dividing sample by the water, in which case it will effectively correct for both, or generating a sensitivity workspace. The latter only captures the detector efficiencies, but does not alter the absolute scale. The advantage of that is that it can be measured once, and reused in many experiments, at any distances and wavelengths. Furthermore, with D22 detector which can be moved laterally, one can perform water measurements with and without lateral offset to obtain the efficiency map without a beam stop shadow in the middle. When dividing sample by the water, they must be in the same units; that is, either both in absolute scale (already divided by the empty beam flux), or both not in absolute scale. Otherwise the algorithm will throw an error. In case they are not in absolute scale individually, they must be measured with the same distance. In the contrary, if both are already in absolute scale (so divided by the respective empty beam fluxes), the water normalisation can be safely done, even if the water is at a different distance. This is typically the case, as at large distances, water does not scatter enough to have a reasonable statistics in a short time. The absolute water cross-section must be relatively flat as a function of Q, and around 0.9 - 1.0 depending on the wavelength. Corrected water measurement is also referred to as flat field.

Solvent¶

One can perform solvent (buffer) subtraction in 3 ways:

• Reducing both the solvent and the sample as samples, then subtracting the 1D curves I(Q). This is the recommended way if the solvent doesn’t have much statistics, in which case pixel-by-pixel subtraction in 2D might be tricky.
• Providing the solvent in the container as an empty container. In this case, when doing empty container subtraction, it will effectively subtract also the solvent. This is the recommended way, if the solvent and the sample are measured in the same empty container.
• Process the solvent as Solvent, then subtract it from the sample. In this case the subtraction will be done pixel-by-pixel in 2D. This is the only way if the solvent is measured in a different container than the sample.

Therefore, this process type is useful only in the case 3 above.

Sample¶

Below is the treatment of the samples. This is similar to the solvent diagram above (solvent is treated just as a sample), except that here one can also provide the solvent input for the subtraction. Sample runs can be standard monochromatic, or kinetic. It is not allowed to have a duplicated run number in the runs list. It will concatenate the runs along the a-axis of the workspace, corresponding to the listing dimension in the input files. Sample runs can have blanks corresponding to missing measurements, see the dedicated section below.

Full Treatment¶

Full treatment is built by stacking up unary reductions with corresponding ProcessAs. The diagram below illustrates the flow of processing. Letters denote the dark current (Cd/B4C) (DC), empty beam (EB), transmission (TR), empty container (EC), flat field (water) (FF), solvent (buffer) (SB), and sample (SA).