In the exciting arena of the solar neutrino research a new actor is expecte
d to come soon in the game: Borexino. This massive, calorimetric, liquid sc
intillation detector, in advanced phase of installation in the underground
Gran Sasso Laboratory, will be focused towards one of the fundamental issue
s of this field, i.e, the direct determination of the flux of the neutrinos
produced in the Be-7 electron capture reaction in the Sun. As a. pilot pro
gram for the full detector, the Counting Test Facility operated for two yea
rs at Gran Sasso, provided the convincing evidence that the fundamental tec
hnological challenge of the experiment, the achievement in the scintillator
of unprecedented radiopurity levels, can be accomplished successfully, thu
s opening the way to the realization of the experiment.