FAZIA (Four π A and Z Identification Array) is a 4π detector for charged particles optimized for studying Thermodynamics and Dynamics of colliding exotic nuclei. It is designed to operate at stable and radioactive beam facilities around the so-called Fermi energy domain, like SPIRAL2. Physicists of the INFN (Italy) co-operate with French, Romanian, Polish and Spanish colleagues, within the European project SPIRAL2 Preparatory Phase, in order to improve the identification techniques of charged particles produced in nuclear reactions.
To this aim, the Collaboration has been extensively studying and improving the discrimination procedures based on the Pulse Shape Analysis (PSA) of signals in Silicon, as each FAZIA telescope includes two layers of Silicon and one crystal of CsI(Tl). The first two Si elements act as a high-resolution telescope with a very low-energy identification threshold, thanks to PSA of ions stopped in the first Silicon.
A series of experiments have been initially performed at IPN Orsay, GANIL in Caen and LNL in Legnaro to study the signals produced by fixed-energy, known-charge and known-mass ions stopped in Silicon.
The experience gained about Silicon material and digital signal processing has permitted FAZIA to identify and overcome the existing limiting factors for PSA in Silicon: insufficient doping uniformity as well as channeling effects. Now they are under full control, so that charge separation and clear mass identification is observed for ion stopped in Silicon, over a significant energy range, for many elements. As a matter of fact, a recent experiment at LNS (Catania) with a test beam of 84Kr at 35 MeV/n showed an unprecedented full Z discrimination up to Z=36 for stopped ions in Si.