The shower tail catcher scintillator S4 improves the PAMELA electron-hadron separation by measuring shower leakage from the calorimeter. It also provides a high-energy trigger for the neutron detector. It consists of a single square piece of 1 cm thick scintillator of dimensions (48×48) cm2 which is read by six PMTs placed along the two opposite sides. The scintillator has a total weight of 4 kg and a global power consumption is 5 W and is placed directly beneath the calorimeter.
