The Anticoincidence Shield of the PAMELA Space Experiment

The PAMELA space experiment will be launched in 2004 onboard a Russian Resurs DK1 satellite, orbiting Earth at an altitude of 300-600 km. The main scientific goal is a study of the antimatter component of the cosmic radiation. The semipolar orbit (71°) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV-190 GeV) and positrons (50 MeV-270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio He{bar}/He below 10^-7. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoincidence shield. The anticounter scintillators are used to aid in the rejection of background from particles not cleanly entering the acceptance of the tracker. Information from the anticounter system will be included as a veto in a second level trigger, to exclude the acquisition of events generated by false triggers. The construction of the anticounter system is described, along with its functionality and performance. The custom read-out electronics and the LED-based monitoring system are also described in detail. Test-beam, simulation and qualification studies of the system are reviewed.