WISRD Research & Engineering Journal

Figure 5 . This is an expected threshold curve using cable set 2 with paddle 1

paddle 2, channel 2, cable 2 (.809v)

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Figure 6 . This is an expected threshold curve using cable set 2 with paddle 2. To determine the optimum operating voltage for each of the photomultipliers (PMTs) the voltage on channel 1 was raised until it detected 40 – 60 counts per second. Using this voltage, PMT’s 1 and 2 were stacked, and counters were set to count when a signal was coincident to channels 1 and 2. The voltage on channel 2 was then swept from .550 - .755 mV. A plot of the counts on the varying channel 2 and the coincidence count vs voltage can be seen in Figure 7.

Figure 7 . Plateauing channel two using channel one as a fixed voltage (ch 2 - .722mv). Note that as the voltage is increased, there is a point where the coincidence count levels off. That point is the ideal operating voltage for the PMT. Once channel two was optimized, it was used as the fixed voltage and channel 1 was swept to find its plateau (Fig 8).

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