Development of a Liquid Scintillator and of Data ... - Borexino - Infn

3 The Counting Test Facility (CTF) of Borexino
Homogeneous Distribution of PMTs
The CTF has 100 PMTs to have a photoelectron (pe) yield big enough to measure energies
as low as a few keV, but only 64 electronic channels (due to funding reasons). Therefore, 72
PMTs are fanned together in pairs, and only 28 PMTs are single electronic channels. In the
CTF1 the distribution was chosen as shown in fig. 3.4, a and b. Having only few electronic
channels at the top and bottom ring leads to a spatial resolution that is much worse in the
z-direction than in the x and y direction. As could be shown with a Monte-Carlo simulation
(MC), the spatial resolution can be improved by putting single channels on the top and bottom
ring, and arranging all the PMTs at the equator rings as double channels (see fig. 3.4, c and
d). Distributing all the PMTs homogeneously over the rings, improves the homogeneity of the
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Figure 3.4: Schematic drawing of the distribution of the PMTs and electronic channels over the
rings of the support structure.