05/19/2011 n's detector threshold calibration source/(w/source)

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Below are my counts rate measurements as function of threshold voltage for n's detector. The source was CF252. The distance between source and n's PMT was about 50 cm. It was 1 PMT set up detector and experiment was hold in LDS on May 19 2011.

First the counts rate was calculated as:

[math]\mbox{Rate} = \frac{N_{\mbox{source}} - N_{\mbox{w/source}}}{\mbox{Time}}[/math]

First I did my calibration for power supply voltage -1250 V:

Second I did my calibration for power supply voltage -1500 V:

And bellow I overlay both cases (-1250 V and -1500 V)

There are no any plateaus, so what is the threshold should be?. Or maybe we are need to look at something different.

Let's recalculate all data using the formula:

[math]\mbox{Ratio} = \frac{R_s - R_{w/s}}{R_{w/s}}[/math]

Below my data and calculations for the case of -1500 V power supply voltage:

Below my data and calculations for the case of -1250 V power supply voltage:

And below I overlay my results (linear scale):

and for log scale:

There are two important conclusion at least for this type of PMT was used:

1. The desirable threshold is about -50 mV
2. The power supply voltage is as expected -1500 V (there are no plateau for -1250 V)

And also some difference with