Steps of nonlinearity determination
In order to determine the nonlinearity curve of a measurement system, first take some measurements with calibration sources, and import them into your HyperLab database.
Our example will work with HyperLab's sample spectra belonging a measure­ment setup with 70 keV - 3300 keV range.
Please load the spectrum files into the database and also set their corresponding source values, as specified in section “Importing sample spectra”.
Perform a batch or individual evaluation on all measurements, and open a multi-line spectrum with the Peak evaluator. Check the FWHM calibration, and adjust the region fits, if necessary. Finally save the peak list, which will be input for the nonlinearity evaluation.
When all measurement are properly fitted, similar statistics will be displayed about them at the right side of the Main Module window as you can see in this picture.
Open Analyses node under your project, then click on Nonlinearity analyses and select Create a new nonlinearity analysis task.
A new window appears now, where basic parameters of nonlinearity fit algorithm may be specified.
You can specify a descriptive name of the new nonlinearity analysis, and thresholds for the identification of peaks.
The Peak identification limit is used when peaklist peaks and nuclear library peaks are matched. If the difference between peak centroids is below this value, the peaks will be considered as matching. Its usual value is 3 channels, which is appropriate for measurement setups with moderate nonlinearity.
The Radiation intensity limit is used when radiations are loaded for a selected decay from the database. The 0.005 default value load the radiations where the intensity is greater than 0.5% of the decay's strongest line. When you are ready, press OK.
The Nonlinearity evaluator appears now with the empty Input data sheet.
Click Add measurement button at the right. The Measurement selector window appears now.
Select the 56Co sample measurement from the project, named COD0111A.DAT.
When you click OK in the measurement selector window, HyperLab performs the steps as follows.
  • Loads the peaks from the most recent peak evaluation of the measurement.
  • Checks if a source is specified for the measurement. If found, loads the source isomers, their decays and radiations.
  • Limits the radiations to those whose intensity is over the preset intensity limit and which have a radiation usage flag stating that the radiation is usable for nonlinearity evaluations.
  • Matches the loaded radiations and peaks, by applying the preset matching limit.
  • If at least 3 matching peak-radiation pairs are found within a peak list, the measurement may be used for nonlinearity evaluation.
  • Checks if enough input data points exist for a polynomial fit. The number of data points must exceed the number of fitted parameters, i.e. the degree of fitting polynomial plus two linear shifting parameters for each measurement.
If enough data points are supplied, the fit is performed and the tab Fit becomes active, displaying the fitted nonlinearity curve.
Now you can add your other measure­ments to the fit one-by-one, or more at a time.
Finally a multi-isotope nonlinearity curve may be constructed.
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