GSI Helmholtzzentrum für Schwerionenforschung
Hello, We have been playing with the first chamber produced at GSI. The gas mixture is Ar-CO2 [70-30], in order to work with voltages similar to nominal. The chamber exibited a few tens of nA dark current, associated with signals at the preamp (connected to one particular anode sector) showing a peaked spectrum. We managed to see Sr90 signals, although when trying to read them out another type of sharp noise appeared, caused by the CAMAC activity. This needs to be worked out. We found out that the dark current dissapeared when disconnecting one particular pad connector, located at the bottom of the chamber. The chamber will be opened and cleaned in this area. By putting an Fe55 source at one gas hole, a la Bucharest, we observed in the nearest anode sector nice signals (see attachment), where the CAMAC noise in this case is centered at around 500 ADC counts (sic), and overwhelmed by the 95 kHz of the source. The voltage was 1575 V and the gain estimated to be 12000. The energy resolution is 28% (FWHM), not pedestal-corrected. Best regards, Herbert and Chilo