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

3 The Counting Test Facility (CTF) of
Borexino
3.1 Motivation
At the end of the last chapter I discussed the extremely high requirements on the radiopurity of
the detector components for a successful neutrino detection in BOREXINO. Standard analysis
methods, such as mass spectrometry or gamma spectroscopy, are sufficient to check most of
the outer detector components on their radiopurity, but the demands on the radiopurity of the
scintillator itself are beyond the sensitivity of these other methods, the only exception being
the high sensitivity neutron activation analysis (NAA) developed in Munich during the last
few years [Gol97, vH99]. To study and check the feasibility of the BOREXINO experiment
in terms of radiopurity of the liquid scintillator and the other detector components, a 5 tonprototype
of BOREXINO was constructed in hall C of the Gran Sasso Underground Laboratory,
the Counting Test Facility (CTF). The main goals of the CTF were:
- measurement of the U and Th content of the liquid scintillator with a sensitivity of
g/g;
- measurement of the ratio at a level of ;
- determination of the optical properties of the liquid scintillator;
- radioactivity screening of the construction materials of various detector components;
- test of several purification methods for the liquid scintillator and the shielding water;
- implementation of methods for cleaning and controlling dust and air impurities during
the detector construction;
- development of analysis methods to discriminate different classes of background events.
K and Be cannot be tested on a level relevant for BOREXINO because the detector is not big
enough to provide sufficient shielding from external background.
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