GBS Elektronik MCA-527 How to do an optimum setup - Manual (Page 7)

Shaping time
The shaping time defines, how many data points are used for averaging the signal height. The shaping time is
half the integration time, so a shaping time of 1µs means that 2µs (=20sample values) before and 2µs after the
signal rise are used to calculate the amplitude value.
Optimum shaping time depends on the noise characteristic of the detector and further there is a trade off between
resolution and high count rate capability. Detectors with a low amount of high frequency noise, like almost all
scintillation detectors with photomultiplier, can be run with a short shaping time like 0.1-0.2µs. For
semiconductor detectors or detectors with photodiode, high frequency electronic noise is much more an issue
and shaping times in the range 0.8...2µs are optimum. The standard setting of 1µs will do in most cases, and
more than 4µs are seldom useful.
If it is known that very high count rates may occur, the lowest acceptable shaping time should be chosen, e.g. for
spent fuel measurements with CZT detectors 0.7µs shaping time is ok.
PZC
PZC adjustment should be done always, and individually for each detector, whereas most other settings can stay
the same for a whole class of detectors. For doing PZC adjustment, use Setup-Amplifier Setup-PZC adjustment-
Automatic PZC by offset minimization.
Fine gain, number of channels, Energy calibration
Fine gain and number of channels is defined by the application. E.g. for some uranium enrichment
measurements, the 186 keV peak is required to be in channel 300, whereas for other applications a fixed energy
calibration of 0.075 keV/channel is required.
For adjusting fine gain, use Setup-Amplifier Setup-Visual amplifier adjustment and use F4 and F5 to adjust fine
gain coarsely. Then create a ROI around the peak to adjust and use Auto (F10) to do the fine adjustment.
It is worth to mention that 512 channels with fine gain 2 is exactly the same as 1024 channels, fine gain 1 and the
upper 512 channels ignored. So if e.g. for uranium measurement the high energy components in the spectrum
force to choose a rather low coarse gain. Then increasing the number of channels is an alternative to increase
fine gain, with the advantage that also the high energy part of the spectrum can be seen for verification.
USB charging
Switch off for mobile applications. In most cases the battery of the MCA will last much longer than the battery
of a laptop.
Some examples about the influence of setting on the measurement are also found in the manual.
Other settings for use in special cases
Trigger filter
The aim of the trigger filter is to detect signals for further evaluation. Its time resolution is important for pile up
rejection, its sensitivity is important for the lower spectrum cutoff.
For almost all cases the default setting (10-201, double differenciating) is ok and a good compromise between
sensitivity and time resolution.