Transcript Measuring Efficiency

Measuring optimal
voltage and efficiency
of the PMT’s
Measuring Efficiency
► Calculate
the optimum voltage for the detectors.
 We want to do this so that we can find the lowest
voltage at which the detectors can run, while still having
a high efficiency.
 This is so that we do not cause the PMT to overdrive, to
overheat, and to age quickly.
 To accomplish this we find the lowest voltage that can
be used to reach the efficiency plateau. This plateau is
reached when raising the voltage does not dramatically
increase the efficiency.
Measuring Efficiency
►
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To find this plateau we set up the
detectors in a vertical column.
We then set the top and bottom
detectors to a fixed high voltage
(we set ours to 1400 V)
Then set the two middle detectors
to a low voltage, collect data,
increase the voltage and repeat
We find efficiency by comparing 2fold trigger rates with 3-fold rates.
Measuring Efficiency
► Data
for one of our
detectors.
► We ran from 950V to
1500V in 50 V
increments.
Voltage
Efficiency
950
0.0571
1000
0.0883
1050
0.1405
1100
0.2122
1150
0.3040
1200
0.4223
Efficiency/Voltage Calibration
1250
0.5448
1300
0.6546
1350
0.7808
1400
0.8800
1450
0.9109
1500
0.9366
AHS PMT #3
9/22/2004
Triggers: 1400V
Threshold: 70 mV
Measuring Efficiency
Efficiency/Voltage scan #3, 9/22/04 (70 mV threshold)
1
0.9
0.8
Efficiency
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
900
1000
1100
1200
1300
Voltage
1400
1500
1600
Measuring Efficiency
► Prepared
By
 Patrick Kane
 Simi Hamilton
 Kelsi Coia
► Under
the Supervision of
 Marc Whitley