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User name mcfarlan
Log entry time 09:24:15 on June 20,1998
Entry number 5800
keyword=Neutron Detector rates
Rates were measured for two bars and two paddles as follows:
Beam 150 nA, target 2 mm carbon, no raster.
All HVs were off except that the following were set at the nominal voltages:
bars 11,12; paddles 13, 30 (30 is in second layer behind 13, these partly overlap bar 12)
The threshold of the discriminators on the bars was 50 mV.
OR of bars: 80 kHz
OR of paddles: 9.5 kHz
Paddle 30: 9.5 kHz
Paddle 13: 5 kHz
A few minutes later:
Bar 11 only: 66 kHz, Bar 12 only: 77 kHz
OR of 11, 12: 137 kHz.
Conclusion: most bar ORs are distinct and are neutrals, most paddle counts are charged and both paddles are involved, the charged rate is a small fraction (20%?) of the neutral rate.
Extrapolating to the experiment luminosity (x3) and assuming all bars equal (x80),
the bar OR may run at 3x40x70 kHz = 8 MHz.
In the meantime, the PMTs may be giving a current of 200 microamp, or 0.7 C/h.
For 1,000 h run, this is close to 700 C from each PMT, at which large gain changes can be expected. In any case the manufacturer recommends <30 microamp for gain stability; the max. average current is 200 microamp.