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PEARLTransfit v1¶

Summary ¶

Reads high-energy neutron resonances from the downstream monitor data on the PEARL instrument,then fits a Voigt function to them to determine the sample temperature. A calibration must be run for each sample pressure. Can be used on a single file, or multiple files, in which case workspaces are summed and the average taken.

Properties ¶

Name	Direction	Type	Default	Description
Files	Input	list of str lists	Mandatory	Files of calibration runs (numors). Must be detector scans. Allowed extensions: [‘.raw’, ‘.s0x’, ‘.nxs’]
FoilType	Input	string	Hf01	Type of foil included with the sample. Allowed values: [‘Hf01’, ‘Hf02’, ‘Ta10’, ‘Irp6’, ‘Iro5’, ‘Iro9’]
Ediv	Input	string	0.0025	Energy step in eV
ReferenceTemp	Input	string	290	Enter reference temperature in K
Calibration	Input	boolean	False	Calibration flag, default is False in which case temperature measured
Debug	Input	boolean	False	True/False - provides more verbose output of procedure for debugging purposes
EstimateBackground	Input	boolean	True	Estimate background parameters from data.
Bg0guessFraction	Input	number	0.84	Starting guess for constant term of polynomial background is calculated as Bg0guessScaleFactor*y0 wherey0 is the intensity in the first bin of the data to be fitted.
Bg1guess	Input	number	0.0173252	Starting guess for linear term of polynomial background.
Bg2guess	Input	number	4e-07	Starting guess for quadratic term of polynomial background.

Description ¶

PEARL high-pressure, high-temperature measurements rely on the use neutron transmission data to determine the sample temperature. Typically Hf foil is included with the sample, though others can be used, provided they have well characterised resonances. Transfit is an algorithm which reads high-energy neutron resonances from the downstream monitor data on the PEARL instrument. It fits a Voigt function to them to determine the sample temperature. It is broadly similar to the Fortran77 version originally implemented on PEARL through OpenGenie. As currently coded – this is only appropriate for use on the PEARL instrument.

Full details of how the temperature information is extracted from the peak shape parameters, can be found in the references below. Essentially, there are two components contributing to the peak shape, the Gaussian and Lorentzian. First, the calibration run must be performed to fit the instrument contributions to the line-shape, and account for any other effects to the line-shape at a given sample pressure. After this, only the Gaussian component is fitted to extract the temperature. Note that a recalibration is required for each given sample pressure.

References ¶

‘Temperature measurement in a Paris-Edinburgh cell by neutron resonance spectroscopy’ - Journal Of Applied Physics 98, 064905 (2005) ‘Remote determination of sample temperature by neutron resonance spectroscopy’ - Nuclear Instruments and Methods in Physics Research A 547 (2005) 601-615

Categories: AlgorithmIndex | Diffraction\Fitting