( ≈ 100 kg of highly radiopure NaI(Tl) detector)
Preliminary informal tests with commercial NaI(Tl) were performed
underground at end of the 80's. Then, after the setting of the DAMA proposal
to INFN on 1990, various R&D developments and detectors were realized,
achieving also some interesting results.
In 1996, a devoted study of the response to nuclear recoils induced
by single neutron elastic scatterings in NaI(Tl) has been performed at
ENEA-Frascati. Moreover, the comparison of the time behaviours between
reference pulses for Compton events and recoils has quantitatively pointed out
the possibility to statistically discriminate electromagnetic component of the
counting rate - when investigating the WIMP class of candidates - at reasonable
level by exploiting the pulse shape analysis in the experimental data.
The experimental set-up was made by nine 9.70 kg
low radioactive NaI(Tl) crystals, realized - in the framework of INFN contracts - with
Crismatec company. Four 7.05 kg older detectors were also placed on the top, mainly to
partecipate to special triggers. All the materials of the detectors and those
surrounding them, photomultipliers by EMI and shields were accurately selected
by using the Germanium facility at Gran Sasso, mass and atomic absorption
spectrometers and - with the highest sensitivity - testing prototypes deep
underground. In particular, the PMTs were the results of a particular devoted development.
Moreover, also the growing methods and the assembling of crystals were