Determining the Threshold

The method to determine the threshold is basically the same as plateauing a counter singly. The difference is instead of changing the PMT voltage we changed the threshold voltage on the DAQ board. Then the voltage vs. the frequency (counts/minute) was graphed. Where the graph changes to become more linear is about the optimum voltage.

Each position was determined individually. We tried to use each counter with its corresponding position, i.e. counter one for position one. Counter five was used for position three due to a problem found in the wire connection in the photo multiplier tube in counter three. The counters are stacked with four on the bottom and one on the top and counter five taking the place of counter three. In each case the optimum voltage is about the same, about 0.500 volts. Here are the graphs for positions One, Two, Three, and Four.

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Erin Nagelkirk
Last modified: Fri Aug 10 11:37:00 EDT 2007