void SANSDirectBeamScaling::exec()
{
MatrixWorkspace_const_sptr inputWS = getProperty("InputWorkspace");
const double beamRadius = getProperty("BeamRadius");
const double attTrans = getProperty("AttenuatorTransmission");
const double attTransErr = getProperty("AttenuatorTransmissionError");
// Extract the required spectra into separate workspaces
std::vector<detid_t> udet;
std::vector<size_t> index;
udet.push_back(getProperty("BeamMonitor"));
// Convert UDETs to workspace indices
inputWS->getIndicesFromDetectorIDs(udet,index);
if (index.size() < 1)
{
g_log.debug() << "inputWS->getIndicesFromDetectorIDs() returned empty\n";
throw std::invalid_argument("Could not find the incident beam monitor spectra\n");
}
const int64_t numHists = inputWS->getNumberHistograms();
Progress progress(this,0.0,1.0,numHists);
// Number of X bins
const int64_t xLength = inputWS->readY(0).size();
// Monitor counts
double monitor = 0.0;
const MantidVec& MonIn = inputWS->readY(index[0]);
for (int64_t j = 0; j < xLength; j++)
monitor += MonIn[j];
const V3D sourcePos = inputWS->getInstrument()->getSource()->getPos();
double counts = 0.0;
double error = 0.0;
int nPixels = 0;
// Sample-detector distance for the contributing pixels
double sdd = 0.0;
for (int64_t i = 0; i < int64_t(numHists); ++i)
{
IDetector_const_sptr det;
try {
det = inputWS->getDetector(i);
} catch (Exception::NotFoundError&) {
g_log.warning() << "Spectrum index " << i << " has no detector assigned to it - discarding" << std::endl;
continue;
}
// Skip if we have a monitor or if the detector is masked.
if ( det->isMonitor() || det->isMasked() ) continue;
const MantidVec& YIn = inputWS->readY(i);
const MantidVec& EIn = inputWS->readE(i);
// Sum up all the counts
V3D pos = det->getPos() - V3D(sourcePos.X(), sourcePos.Y(), 0.0);
const double pixelDistance = pos.Z();
pos.setZ(0.0);
if (pos.norm() <= beamRadius) {
// Correct data for all X bins
for (int64_t j = 0; j < xLength; j++)
{
counts += YIn[j];
error += EIn[j]*EIn[j];
}
nPixels += 1;
sdd += pixelDistance;
}
progress.report("Absolute Scaling");
}
// Get the average SDD for the counted pixels, and transform to mm.
sdd = sdd/nPixels*1000.0;
error = std::sqrt(error);
// Transform from m to mm
double sourceAperture = getProperty("SourceApertureRadius");
sourceAperture *= 1000.0;
// Transform from m to mm
double sampleAperture = getProperty("SampleApertureRadius");
sampleAperture *= 1000.0;
//TODO: replace this by some meaningful value
const double KCG2FluxPerMon_SUGAR = 1.0;
// Solid angle correction scale in 1/(cm^2)/steradian
double solidAngleCorrScale = sdd/(M_PI*sourceAperture*sampleAperture);
solidAngleCorrScale = solidAngleCorrScale*solidAngleCorrScale*100.0;
// Scaling factor in n/(monitor count)/(cm^2)/steradian
double scale = counts/monitor*solidAngleCorrScale/KCG2FluxPerMon_SUGAR;
double scaleErr = std::abs(error/monitor)*solidAngleCorrScale/KCG2FluxPerMon_SUGAR;
scaleErr = std::abs(scale/attTrans)*sqrt( (scaleErr/scale)*(scaleErr/scale) +(attTransErr/attTrans)*(attTransErr/attTrans) );
scale /= attTrans;
std::vector<double> output;
output.push_back(scale);
output.push_back(scaleErr);
setProperty("ScaleFactor", output);
}