Note: for all these runs in the planetarium, there is a question about the high voltage actually used. I (jt) cannot at this point remember the high voltage arrangements and if the high voltage was checked at the monitor point. Subsequently I have realized that LB draws 1mamp of current in its base, and each of the others draws about 0.4mamp. The limit of the power supply is 2 mamp, so if LB and three others are on the same supply, the voltage will be less than it would be for only the three others. On July 11 we found for UMSL HV 8, that the difference was from 1850V to 1650V. This may explain why the efficiencies below are somewhat less than expected from the estimated one pe signals and thresholds.
Efficiency Runs July 29, at 1900 V, All 4 required, ~ 2 min.
For the runs taken July 30, since some data had been taken at 1900V and we were changing the HV to 1830, efficiencies were taken at both settings. The counters were tested for efficiency one at a time, disabling the one under test from participation in the trigger. Lenka B (LB) was placed cross-wise to the stack, pulled back from full overlap to about 3 inches (rather than the approx. 18 inches available, in order to avoid running events together (and thus losing the 0 status bit which normally indicates the last record in an event). The order of the counters in the stack (with PMT's pointing oppositely, as usual), is:
One pe sizes at 1900 V were: 10-15mV, 15-20mV, 7mV for 10A,7C,10B.
One pe sizes at 1800 V were: 7-8mV, 7mV, 2-3mV for 10A,7C,10B.
Thresholds were: -.29,-.29,-.292,-.33 for inputs 1-4 for 1900V runs.
Thresholds were: -.29,-.29,-.292,-.15 for inputs 1-4 for 1830V runs.
There is approximately an amplification of 11, so that the thresholds corresponded to 27mV, 27mV, 27mV, and 30 mV for 1900V runs, and 27mV, 27mV, 27mV, and 13mV for 1830V runs. Therefore these corespond to pe thresholds of approximately: 2pe for 10A and 10B at 1900V and 4pe at 1800V (somewhat lower threshold at 1830 V), and 4-5pe for 7C for the 1900V runs and somewhat less than 5 pe for the 1830 V runs.
These thresholds can be compared to observed light yields of :
counter far from PMT middle near PMT
7C 7-8 16 41
10A 5 6 23
10B 8 12 30
Efficiency Runs July 30, at 1900 V, triples, input 2 not required
Efficiency Runs July 30, at 1900 V, triples, input 3 not required
Efficiency Runs July 30, at 1900 V, triples, input 4 not required
Efficiency Runs July 30, at 1830 V, triples, input 2 (8A) not required
Efficiency Runs July 30, at 1830 V, triples, input 3(7C) not required
Efficiency Runs July 30, at 1830 V, triples, input 4(10B) not required