Deadtime correction using the X23A2 Vortex
Contents
Installing on Windows
In these instructions, %APPDATA% = C:\Documents and Settings\bravel\Application Data\ on my computer. On your computer, bravel will be replaced by your login name.
Put the X23A2MED.pm file in the folder %APPDATA%\horae\Ifeffit\Plugins\Filetype\Athena\
Put the x23a2vortex.ini file in the folder %APPDATA%\horae\.
Follow the instructions in the Athena document to verify that the plugin was installed and loaded correctly and is enabled for use by Athena.
Installing on Unix
In these instructions, $HOME = /home/bruce on my computer. On your computer, bruce will be replaced by your login name.
Put the X23A2MED.pm file in the folder $HOME/.horae/Ifeffit/Plugins/Filetype/Athena/
Put the x23a2vortex.ini file in the folder $HOME/.horae/.
Follow the instructions in the Athena document to verify that the plugin was installed and loaded correctly and is enabled for use by Athena.
Using the plugin to correct your data for deadtime
When you import data that the plugin recognizes as coming from the X23A2 Vortex, you will presented with a dialog for inputting the parameters of the correction. Most of them are for identifying which column is which. Each channel must also have its deadtime corrected. The deadtime for our detector using our electronics is about 280 nanosecond for each channel. Entering 0 nanoseconds for the deadtime will cause the algorithm to use the standard fast/slow (aka ICR/OCR) correction rather than the full deadtime correction.
After clicking through the deadtime parameters dialog, you will be presented with the standard column selection dialog for which the columns include the deadtime corrected data for each channel. From here, proceed as you do for normal data.
How the correction works
With the plugin installed and enabled, you will be presented with this dialog when you import a file measured with the X23A2 Vortex:
As you can see, there are ways to specify the energy and I0 columns as well as the either the column with integration times or a value for constant integration time. At X23A2, I often use k-weighted integration time, so specifying the column with the integration time is essential. Then, for each channel, you need to specify the deadtime and the column lables for the ROI, the fast signal (i.e. ICR), and the slow signal (i.e. the OCR). Joe measured the deadtimes (using a method I will document at a later date) and found that each channel is about 280 nanoseconds.
If the deadtime is known for a channel, that will be used to correct the fast channel (aka input count rate, or ICR) by iteratively solving the analytically unsolvable equation which describes the attenuation of the fast channel due to deadtime:
where τ is the deadtime, x is the actual input rate on the fast channel, and y is the measured rate on the fast channel. The iterative solution solves point-by-point and for each channel for x using a value for τ and the column containing y.
If the deadtime is set to 0 (or negative) for a channel, then the standard correction of the ratio of the fast and slow channels (or ICR/OCR) will be applied to that channel. Thus it is very simple to compare the full correction with the standard correction.
For high count rates, the proper deadtime correction is considerably more accurate than the standard correction. We will be writing a paper on this soon.
Sadly, this plugin breaks one of the nice features of Athena -- multiple data file import. This dialog will appear for each file, requiring you to click through this then the column selection dialog for each file. Sigh....
A few more notes
- The ROI (region of interest) is set by the adjusting the discriminator window of the single cahnnel analyzer.
- The fast channel is the ICR output from the Vortex.
- The slow channel (aka OCR) is the signal from the SCA using a discriminator window that covers essentially the entire output range.