The PARIS detector (Photon Array for studies with Radioactive Ion and Stable beams) will provide cutting edge technology for the detection of gamma rays emitted by nuclei produced at high rotational velocities by SPIRAL2 high-intensity beams of neutron-rich ions.
A working group, composed of Polish, French, English, Bulgarian, Hungarian and Indian scientists, is carrying out the design work necessary to optimize the gamma detection, in the framework of the European project SPIRAL2 Preparatory Phase.
In this aim, the GEANT 4 simulation software PARIS has been developed, assuming two segmented concentric spherical shells, cubic shells and tilted cubic shells (built as a cube in which individual modules are on average at the same distance from the target position), made of different scintillators.
The GEANT4 PARIS package has been intensively used to understand how gamma-rays are absorbed in a system composed of two layers of scintillators: a LaBr3(Ce) crystal coupled to longer CsI(Na) crystal. The different regimes of gamma-ray absorption (photopeak, Compton, pair creation) have been investigated.
Building a compact array based on a spherical configuration with the current available LaBr3 shapes is quite difficult. This arrangement suffers thus of a consequent lost of efficiency. A cubic like arrangement offers a better full gamma-absorption probability. However, the response function of such a device is more complicated to understand. Compact configurations based on different shapes of LaBr3 crystals (if technically possible) are an interesting alternative. Further studies are in progress to design the best configuration for the PARIS array.