Fitting

A fit consists of markers and parameters and is autonomous, i.e. if you delete the spectrum you have fitted, the fit will still be there. So you may load or activate another spectrum while keeping the markers and use the same fit on it.

To obtain best fit results you have to define fit- and background-regions as well as peak markers. To define the fit-region, i.e. the region of the spectrum containing the peak(s) to be fitted, press r for the left border and press r again for the right border of the fit-region. Now mark all peaks to be fitted inside the fit-region by pressing p over each peak. Then you can perform the fit by pressing F or with the command:

Optionally you can further improve the fit by defining an arbitrary number of background-regions using the hotkey b once for the left and once for the right border of each background-region. Press B to fit spectral background inside the background-regions and F afterwards to fit peak(s). The background fitted to the background-regions will be used for the fit inside the fit-region. Note, though TV supports only one fit-region, any number of background-regions can be defined for the fit. Figure 4.4 on page

shows spectra with fits. In its upper pane no fit parameters have been changed and the fit does not suit very good as you can see.

If you want to save your fit results to a file it must be opened first. To open the file enter the command:

If you want to set new markers to perform another fit, you have to delete the old markers first. Best you can do this by pressing -F. You can recover fit markers that have been deleted accidentally with the command:

**Figure 4.4:** Graphic-display window with a ²²⁶ Ra spectrum loaded and a fit attached. **Upper:** The fit parameters are set to their default values. **Middle:** Left tail parameter is set free. **Lower:** Left tail and step height parameters are set free.
$\begin{figure} \begin{center} \leavevmode \epsffile {pictures/fit-demo-3.ps} \end{center}\end{figure}$

In order to consider the left tail you must allow TV to fit it. The command to do that is:

The result for the fit with tail is shown in the middle pane of figure 4.4 on page

and the difference is evident. You can furthermore consider the background form in various ways. Since there can be a loss of energy in electronics during data aquisition some events are shifted to lower energies and a step in the background will occur. You can fit height as well as width of these steps. To allow TV to fit the height of a step you enter:

The lower pane of figure 4.4 on page

shows the difference in the background form. The step is fitted as arctan but you can also consider an erf-function (see section D.1 p.

). You can do this with the command:

A list of all fit parameter commands is printed in section 6.4.12 on page

. Table 4.6 on page

shows all hotkeys related to the fit commands.

**Table 4.6:** Hotkey definitions for fit markers and commands known by TV.
Hotkey	TV-commands	Function
b	tv $>$ fit mark bg-region enter cursor;	Set background-region marker at cursor position
p	tv $>$ fit mark peak enter cursor;	Set a peak marker at cursor position
r	tv $>$ fit mark region enter cursor;	Set fit-region marker at cursor position
-b	tv $>$ fit mark bg-region delete cursor;	Delete background marker closest to the cursor
-p	tv $>$ fit mark peak delete cursor;	Delete peak marker closest to cursor
-r	tv $>$ fit mark region delete cursor;	Delete fit-region marker closest to cursor
-A	tv $>$ cut mark cut delete;	Delete all markers. You will
	tv $>$ window hide mark cut;	still see markers which are
	tv $>$ fit mark fit delete;	part of the autonomous fit
	tv $>$ fit delete;
	tv $>$ window hide mark fit;
	tv $>$ label user delete all;
	tv $>$ normalization mark delete;
	tv $>$ recalibration marker delete all;
-B	tv $>$ fit mark bg-region delete all;	Delete all background markers
-F	tv $>$ fit mark fit delete;	Delete the current fit and
	tv $>$ fit delete;	all its markers
	tv $>$ fit delete activ;
	tv $>$ window hide mark fit;
Q	tv $>$ fit mark fit delete;	Creates a quick fit.
	tv $>$ fit delete;
	tv $>$ fit mark peak enter cursor;
	tv $>$ fit mark region enter offset -10 offset 20;
	tv $>$ window view full y;
	tv $>$ fit region-create;
	tv $>$ fit status short;
	tv $>$ window show fit function/marker;
-P	tv $>$ fit mark peak delete 0 uncalib 8192 uncalib;	Delete all peak markers
HP	tv $>$ fit parameter peak hold;	Prevent peak position from being fitted
HW	tv $>$ fit parameter width hold;	Prevent peak width from being fitted
Pbh	tv $>$ fit param backgr hold;	Prevent background-parameters
	tv $>$ fit param exponent hold;	from being fitted
	tv $>$ fit param factor hold;
Pbf	tv $>$ fit param backgr free;	Allow background-parameters
	tv $>$ fit param exponent free;	to be fitted
	tv $>$ fit param factor free;
Pwe	tv $>$ fit parameter width equal;
we	tv $>$ fit parameter width equal;
wf	tv $>$ fit parameter width free;	Allow width to be fitted