JMU Quantum Efficiency tests

The Setup

Light Source Two light sources are used in order to determine the relative blue-green quantum efficiency of the R6095 tube. In both sources, a blue led leads through a light pipe in order to approximate an even light level distribution among the five tubes. The green light source is then attached to a green WLS and fed into the photomultiplier housing. The blue light source is similarly fed with a clear optical fiber. The fibers are then optically glued to the face of a cylindrical polished clear plastic medium. This allows for the fiber to illuminate more of the photocathode than simply pressing the fiber to the face of the pmt. This method of illumination covers 41% of the active photocathode

Light Source Stability The green source was previously used, and proved to be stable within 1.5% through our runs. The blue source was not nearly as stable. From day to day, the blue source would fluctuate wildly when tested on a standard tube. The cause for this is still unknown, but the solution was to normalize the data taken on a daily basis. The tubes had to be rotated through a multiple to five tests per day in order to evenly normalize each of the five slots as well as possible. Tests performed to check the accuracy of the assumption that the light source did not change enough during a day to ruin testing suggest a maximum variation of 6.2% during a single testing day period.

The results Relative Blue to Green quantum efficiency of the 80 tested PMTs as measured in Anode Current by use of a constant gain.