ReflectometryBeamStatistics v1¶

Summary¶

Calculates statistical quantities of a reflectometry workspace.

Properties¶

Description¶

This algorithm computes quantities needed by ReflectometryMomentumTransfer and ReflectometrySumInQ, and adds the results to the sample logs of ReflectedBeamWorkspace. The following sample logs get added:

beam_stats.beam_rms_variation

$=2 \sqrt{2 \ln 2} s \sqrt{\sigma}$, where $s$ is PixelSize and $\sigma$ is the variance of the intensity (integrated over all wavelengths) distribution of the detectors in the foreground region.

beam_stats.bent_sample

1 if the sample can be regarded as non-flat and the beam is collimated, 0 in the case of divergent beam.

bean_stats.first_slit_angular_spread

$=0.68 x_{slit1} / d_{slits}$, where $x_{slit1}$ is the size of the first slit and $d_{slits}$ is the distance between the first and second slit.

beam_stats.incident_angular_spread

$=0.68 \sqrt{x_{slit1}^2 + x_{slit2}^2} / d_{slits}$, where $x_{slit1}$ is the size of the first and $x_{slit2}$ the size of the second slit while $d_{slits}$ is the distance between the slits.

beam_stats.sample_waviness

The heuristically calculated root mean squared sample waviness.

beam_stats.second_slit_angular_spread

$=0.68 x_{slit2} / (d_{slit2} + l_2)$, where $x_{slit2}$ is the size of the second slit, $d_{slit2}$ is the second slit-to-sample distance and $l_2$ is the sample-to-reflected foreground centre distance.

Additionally, beam_stats.beam_rms_variation is cached to the sample logs of DirectLineWorkspace removing the need to recalculate the quantity every time the same direct beam passed to this algorithm.

Usage¶

Example - ReflectometryBeamStatistics

dir = Load('ILL/D17/317369.nxs')
ref = Load('ILL/D17/317370.nxs')

ReflectometryBeamStatistics(
    ReflectedBeamWorkspace=ref,
    ReflectedForeground=[199, 202, 205],
    DirectLineWorkspace=dir,
    DirectForeground=[200, 202, 205],
    PixelSize=0.001195,
    DetectorResolution=0.00022,
    FirstSlitName='slit2',
    FirstSlitSizeSampleLog='VirtualSlitAxis.s2w_actual_width',
    SecondSlitName='slit3',
    SecondSlitSizeSampleLog='VirtualSlitAxis.s3w_actual_width')
run = ref.run()
bent = run.getProperty('beam_stats.bent_sample').value
print('Bent sample? {}'.format('yes' if bent == 1 else 'no'))
rms = run.getProperty('beam_stats.beam_rms_variation').value
print('Beam RMS variation: {:.3}'.format(rms))
run = dir.run()
rms = run.getProperty('beam_stats.beam_rms_variation').value
print('RMS variation cached in dir: {:.3}'.format(rms))

Output:

Bent sample? no
Beam RMS variation: 0.00236
RMS variation cached in dir: 0.00208

Categories: AlgorithmIndex | ILL\Reflectometry | Reflectometry

Source¶

C++ header: ReflectometryBeamStatistics.h

C++ source: ReflectometryBeamStatistics.cpp