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7.3.6 SAMPLING OF CSI-PULSES

Data were taken with signals from a CsI-crystal. A typical pulse of a cosmic muon penetrating the CsI crystal is shown in Fig. 7.13 top. The DSC integral plotted as a function of the FB ADC for 3000 events is shown in Fig. 7.13 bottom.

The random cosmic-muon trigger makes one problem of the DSC apparent. The value of the baseline is dependent on the elapse-time between triggers. This effect is assumed to arise from a time dependent static charging of the sampling capacitors. The effect varies from chip to chip. The time constant was determined and is a few 100ms. At a constant trigger rate above 50/s the random baseline fluctuation disappears. This problem can be solved by applying an additional "flash frequency" of 100Hz to the DSC. However, for a new version of the chip, this problem will be solved by use of an additional switch, which keeps the sampling capacitors at a constant potential, except for the sampling and the readout phase.


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