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DepolarizedAnalyserTransmission v1¶

Summary ¶

Calculate the transmission rate through a depolarized He3 cell.

Properties ¶

Name	Direction	Type	Default	Description
DepolarizedWorkspace	Input	MatrixWorkspace	Mandatory	The fully depolarized helium cell workspace. Should contain a single spectra. Units must be in wavelength.
EmptyCellWorkspace	Input	MatrixWorkspace	Mandatory	The empty cell workspace. Must contain a single spectra. Units must be in wavelength
PxDStartingValue	Input	number	12.6	Starting value for the depolarized cell transmission fit property pxd.
StartX	Input	number	1.75	StartX value for the fit.
EndX	Input	number	14	EndX value for the fit.
IgnoreFitQualityError	Input	boolean	False	Whether the algorithm should ignore a poor chi-squared (fit cost value) of greater than 1 and therefore not throw an error.
OutputWorkspace	Output	TableWorkspace	Mandatory	The name of the table workspace containing the fit parameter results.
OutputFitCurves	Output	MatrixWorkspace		The name of the workspace containing the calculated fit curve.

Takes a pair of monitor-normalised, single-spectra workspaces representing a depolarized helium cell and the empty cell to calculate the transmission of the depolarized cell, as described by Wildes [1] and by Krycka et al. [2].

\[T(\lambda) = T_E(\lambda) * exp(-\mu) = T_E(\lambda) * exp(-0.0733 * p * d * \lambda)\]

We first normalise the depolarised workspace \(T(\lambda)\) by the empty cell workspace \(T_E(\lambda)\), accounting for the neutrons lost to the glass cell and only considering the helium inside:

\[\frac{T(\lambda)}{T_E(\lambda)} = exp(-\mu) = exp(-0.0733 * p * d * \lambda)\]

We can then determine the cell path length multiplied by the gas pressure \(p * d\) by using an exponential fit to the curve of \(exp(-0.0733 * p * d * \lambda)\). The parameters table is then output, allowing for \(p * d\) (PxD) to be used in further corrections. Optionally, the calculated fit curves can also be output. See Fit v1 for more details.

A polarised He₃ cell decays over time. At the end of its life, the cell is be actively depolarized and a run is created to find the depolarized transmission rate through the helium. This allows for more effective efficiency corrections.

When depolarized, \(P_{He} = 0\), allowing the transmission to be be determined using the above equations.

Usage ¶

Example - Calculate Transmission

# Create example workspaces.
CreateSampleWorkspace(OutputWorkspace='mt', Function='User Defined', UserDefinedFunction='name=LinearBackground, A0=-0.112, A1=-0.004397', XUnit='wavelength', NumBanks=1, BankPixelWidth=1, XMin=3.5, XMax=16.5, BinWidth=0.1)
CreateSampleWorkspace(OutputWorkspace='dep', Function='User Defined', UserDefinedFunction='name=ExpDecay, Height=0.1239, Lifetime=1.338', XUnit='wavelength', NumBanks=1, BankPixelWidth=1, XMin=3.5, XMax=16.5, BinWidth=0.1)

output = DepolarizedAnalyserTransmission("dep", "mt")

print("PXD Value = " + str(output.column("Value")[0]) + ".")