FalconX1/X4/X8 Quick Start Guide
Version 0.6
August 23, 2019
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‘very-short’ (around 300 nanoseconds) to ‘long (around 2 microseconds).
The shorter decay times are meant to support the highest counting rate
operation. SDD detectors will use wither the ‘short’ or ‘very-short’ settings;
HPGe detectors, which have higher noise, can benefit from the longer decay
times.
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Gain and offset control
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The signal gain can be adjusted over a range of x1 to x16 in fine steps (as
12-bit DAC is used)
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The signal offset can be adjusted so that the baseline value can be placed
anywhere in the ADC range. By default, it is in the center of the range.
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The screenshot above shows the signal from an SDD, with the polarity set to give
positive-going pulses and the gain set to give a reasonable step size.
2.3 Pulse Characterization
Once the analog settings have been adjusted, the next step is to characterize the pulse,
or measure the shape of the pulse; it is necessary to have this characteristic pulse
shape prior to collecting MCA data (the MCA will not operate if there is no
measurement of the pulse shape). For this step, it is best to have a signal from a
simple spectrum (Fe55 or metal foil target), at a moderate count rate (up to 100 kcps
– most pulses should be isolated when looking at a Scope trace). To start the
Characterization process, either press th ‘Characterize’ button in the setup panel on
the left, or choose the Characterization tab on the right and press the ‘Characterize’
button at the top. In either case, the Characterization tab will be activated, and you
will see a progress bar along the top. Once the process ends, the display will be
updated with the fitted pulse shape, where you will see three curves: a sample pulse,
the initial fitted shape based on a sum of two exponentials, and the final pulse shape
which is a refined version of that fit.