Performance assessment tests of multi-anode photomultiplier tube at Jefferson Lab

Abstract

In nuclear physics, photomultiplier tubes (PMTs) are used to detect scintillation light resulting from high-energy reaction products for collision events passing through detector materials. The Thomas Jefferson National Accelerator Facility (JLab) in Newport News, VA received six hundred and two (602), 16-channel, Multi-Anode PMTs from Fermilab's decommissioned CDF experiment. These PMTs are being incorporated into the design and construction of a new Coordinate Detector to be located in Hall A. Of the PMTs received, one hundred and eighty six (186) were HAMAMATSU H8711 tubes, and four hundred and sixteen (416) were HAMAMATSU R5900-00-M16 tubes. To identify the best-performing PMTs, each tube was tested using a LED light source to analyze the signal response (ADC spectrum) of each of its sixteen pixels. The ADC spectrum in the absence of light, known as noise or dark current, was also characterized for every pixel in each of the PMTs. A statistical analysis algorithm was then used to fit single and double Gaussian distributions to each ADC spectrum, with the double Gaussians needed to account for cases in which the LED spectra exhibited both signal and noise responses superimposed (due to some inherent inefficiency). These fits determined the mean and standard deviation for all of the dark current (noise) and signal (LED) measurements. With this information, the actual signal response of each pixel, the average gain of each tube, and the relative responses for the 16 pixels associated with all 602 PMTs were evaluated. These results were then used to classify the overall performance of the tubes. A total of 347 PMTs were found to have uniform performance with no bad pixels, and the majority of these were found to be operating with average to high gains. Furthermore, another 107 PMTs were assessed as having non-uniform performance with at most a single bad pixel that exhibited a similar range of operational performance as the uniform tubes. These two groups of PMTs represent over 75% of the available PMTs. An additional 120 PMTs were found to have non-uniform performance with at most two to three bad pixels and exhibited average to below average operating performances. The remaining 28 PMTs had five to sixteen defective pixels, were non-uniform, and performed poorly.