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

3.4 The upgraded Counting Test Facility: CTF2
3.4 The upgraded Counting Test Facility: CTF2
3.4.1 Motivation
The CTF1 has continuously operated from January 1995 to July 1997. At the end the number
of PMTs functioning was substantially reduced due to a failure of the sealing of the PMTs.
Therefore the Counting Test Facility was refurbished and upgraded during the years 1998 and
1999 and restarted data taking in May 2000.
The CTF2 will be used as a quality control facility for BOREXINO, its main goals are:
- to test a sample of each batch of scintillator as it is delivered for BOREXINO on its C
content and its radiopurity;
- to test and optimize the BOREXINO liquid handling and purification systems after their
installation on site before the final operation in order to guarantee the high purity standards
requested.
As a first campaign from June to September 2000 an alternative liquid scintillator for BORE-
XINO based on phenyl-o-xylylethane (PXE) was tested. The results of this campaign will be
reported in chapter 6.
3.4.2 Design Improvements
New PMT Design and Readout
The sealing of the PMTs in the CTF1 revealed several serious structural problems that caused
a failure of more than 80 % of them. Therefore, a completely new PMT sealing design was
developed for the CTF2. The part of the tube to be protected, i.e. the pins and the voltage
divider, are enclosed in a cylindrical stainless steel housing filled with several layers of potting
materials (see fig. 3.6). An underwater connector and an underwater cable, the same developed
for BOREXINO, allowed the mounting of PMTs and cables to be done in separate steps. Only
one cable supplies the high voltage and transmits the signal. The capacitive decoupling of the
signal is done in the electronics room. This technique will also be used for BOREXINO.
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