Single photo-electron measurement of the new PMTs
About 10 PMTs have been tested so far from a batch of 25 PMTs.
Difference with the old test of 194 PMTs:
1) CAEN v792N ADC (12-bit with 400pC range) vs old
CAEN v256 ADC (12-bit with 800pC range; 15-bit with 120pC range);
2) No 10x amplifier now which was used in the old measurements;
3) Manual HV power supply.
Old measurement example (ZQ2247):
New measurement example (WA0440):
Two observations:
1) Larger deviations between our measured gains and Hamamatsu-specified
gains: on the order of 10%-20%. Almost all old measurements
had deviation within 10% or less.
2) Do we see a large spread in the photocathode efficiency?
Ratio of the pedestal/SPHE peak heights is from 60:1 (left)
to 28000:1 (right) among 10 tubes. Among 194 old
tubes, this ratio was between 20:1 and 5000:1.
