GBS Elektronik MCA 166 - Manual (Page 18)

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information (integral, area, centroid and FWHM) shown. If the MCA is calibrated, peak
information is shown in keV, otherwise in channels.
The last row of the graphics screens shows the actual functions of the function keys.
(From left -F1- to right -F10- ; on the HP200LX the corresponding function keys are just
below the screen).
3.2.2.2 Setup
Allows to setup the acquire functions like Presets, MCA channels, Threshold, Upper and
lower Level discriminators (LLD, ULD), ADC input and automated repetitive
measurements. The parameters asked for depend on if the MCA is set to MCA or MCS
mode.
Stop condition (Only in MCA mode)
Allows to set the preset choices. Possible are: Real time (just the elapsed time, sec.), live
time (the elapsed time subtracted by the MCA dead time, in sec., default), Integral, Peak
Area (peak integral subtracted by background, see appendix 2 for the formula) and infinite
measurement. For integral and peak area a ROI must be set. Use the space bar to toggle
between the choices.
Value (only MCA mode)
Use this field to input a preset value - this can either be set as the number of seconds or
the number of counts. The maximum number of preset seconds is 65536, the maximum
number of preset counts is 10.000.000 . Default is 300s or counts.
ROI (only MCA mode)
Allows to select one of the ROIs which is used as preset for the integral counts or the
peak area in that ROI.
Channels (MCA mode)
Allows to set the number of MCA channels. Use the space bar to toggle between
128....4096 channels. Note that the last 128 channels of 4096 can not be used and
remain empty (and correspondingly the last 64 of 2048, etc.). Default is 4096 channels.
For a HPGe detector, the choice will be in most cases 4096 channels, whereas for a
CdZnTe detector 1024 channels are enough. For a NaI 256 channels are sufficient.
Channels (MCS mode)
Use the spacebar to select between 128...4096 MCS channels. Default is 4096 channels.
Time per Channel (only MCS mode)
Enter the time per channel in increments of 10 msec.
Threshold
Allows to set a threshold value between 2% and 60% of the current MCA scale
. Default is
2%. This analogue threshold cuts the pulses before they reach the ADC. Setting the
threshold high discriminates unwanted pulses and reduces the dead time of the ADC.
Do visual threshold adjustment
Allows to adjust the threshold using visual control of the spectrum.