The Borexino detector: Photomultipliers system

Borexino, a real-time device for low energy solar neutrino spectroscopy has completed the construction phase at the middle of 2006 in the underground laboratories at Gran Sasso, Italy. The detector has been filled with 1300 tons of highly purified scintillator and 2400 tons of ultra-pure water as external shield and since May 16th is under data taking. The experimental goal is the direct measurement of the flux of Be7 solar neutrinos of all flavors via neutrino-electron scattering in an ultra-pure scintillation liquid. The poster describes the design of the Borexino detector and the features of the construction phase. It also presents in deep details the photomultiplier detection apparatus: the device electrical performances, the encapsulation design, the mechanical support, the R and D ageing test and finally the 'in situ' installation procedure.