The GARFIELD apparatus consists of two drift chambers filled at low pressure (50-70 mbar) with CF4 gas. They are essentially two cylindrical shaped containers, where a structure with drift electrodes and partition cage are lodged to obtain an uniform electric field for the drift of electrons and ions formed along the incident particle ionization track.
Inside the same gas volume there are:
- gas micro-strip detectors which are lodged almost perpendicular to the beam axis and have the function of amplifying the electrical signal by a factor 30. They give the information on the energy loss ΔE of the detected products.
- 180 CsI(Tl) crystals (4x24 in the forward chamber, 4x21 in the backward chamber) which give the information on the residual energy Er.
The forward chamber covers the angular range in the laboratory framework from θ=30° to θ=85°, while the backward one goes from θ=95° to θ=150°.
The reaction products, which are emitted during the Heavy Ion nuclear collisions at the Tandem- Alpi energies (5-20AMeV), cross radially the gas region and stop in the CsI(Tl). Their energy and charge identification is obtained mainly through the ΔE-E technique.
The GARFIELD drift chambers are normally coupled with ancillary and/or trigger detectors.
Among them BaF2 crystals from the HECTOR/HELENA apparatus have been used for high energy γ-rays (10-15MeV) in γ-ER-LPC measurements (GDR Dipole emission from Compund Nucleus, fast emission of dynamical dipole, isospin mixing etc.)
PPAC-PS or, in alternative, phoswich detector systems have been used for ER and forward angle detection purposes.
A RINGCo system (three stage annular telescope) has been also used for thermo-dynamical studies of hot nuclei. This system is made by 8 axial Ionization Chambers, followed by 8 sectors of Si (300mm), each of which divided in 8 strips, followed again by 64 (8x6) CsI(Tl) crystals. This high granularity system permits to perform high resolution measurements (both in terms of energy, mass, charge and position) where correlation functions can be reconstructed. Techological Innovation: the GARFIELD apparatus is working since ten years but recently have been renewed as far as the electronic processing of the signals: close to the dedicated analog electronic custom developed within the group both from Naples electronic workshop (FAIR acquisition system) and Milano electronic workshop (pre-amplifiers and shapers), we have now available a new digital system which was developed from the Florence and Naples collaboration. The digital electronics, based at the moment on fast ADC 12-bit at 125MSamples/s and on DSP for the processing. This digital electronic cards have been developed as a first phase toward the FAZIA apparatus development.
Physics with GARFIELD
The possibility of coupling GARFIELD with different trigger and ancuillary detectors permits to use the whole system for different research themes: Among them we deal mainly with:
- central collisions and nuclear thermo-dynamics: study of the behaviour of nuclear matter and of nuclear parameters which characterize the nuclear equation of state (phase diagram, caloric curve, symmetry energy)
- semi-peripheral collisions and nuclear dynamics: deep inelastic collisions, study on the viscosity and friction in nuclear matter, energy and angular momentum dissipation, PLF and TLF energy repartition, neck emission and characterization of nuclear matter in extreme conditions of density.
- pre-equilibrium and Clustering emission: competition between equilibrated thermal emission and fast processing. Pre-cluster formation in a-cluster systems and specific a-emission from compound nuclei formed with a-cluster and non a-cluster projectiles.