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Gain Testing with a Portable MCA System

J. Messimore

Over the course of the next three months, the gain testing of more than 800 PMT's will take place in Sendai and allow for an accurate assessment of the number of new tubes to be manufactured. Due to contraints on time and equipment, a simpler setup was devised that consists of an amp, pre-amp, and an multi-channel analyzer (MCA) along with a LED/pulsar system. While we are still testing the possibility of detecting single photoelectron peaks using a gate and delay generator with this system, it will allow us to accurately and quickly determine the relative gains of the PMT's.

Using a light tight box and the aforementioned equipment, a single 20 inch PMT was gain tested. The LED/pulsar system was run at 10 kHz over a broad range of high voltage (1500 - 2300 volts) on the tube. Using the MCA, the centroid channel of the signal was obtained and used to produce the following plot of the relative gain versus high voltage.

Due to the wide range of high voltage on the tube, the gain on the amp had to be changed periodically in order for the centroid to be seen. Therefore, the values on the above plot were normalized to an amp gain of 20. Lastly, the full width at half max was calculated for each point and the results were very consistent, showing an average resolution of 59.9%.

Last updated: September 13, 1999