ToF – Time of Flight

The Time-of-Flight (ToF) system of PAMELA comprises 6 layers of fast plastic scintillators (Bicron BC-404) arranged in three planes (S1, S2, S3), with alternate layers placed orthogonal to each other.

The distance between S1 and S3 is 77.3 cm. Time of flight information for charged particles passing between planes S1 and S3 is combined with track length information derived from the magnetic spectrometer to determine particles velocities and reject albedo particles. Ionization (dE/dx) measurements in the scintillator layers allow the particle charge to be determined at least up to Z=8. Coincidental energy deposits in combinations of planes provide the main trigger for the experiment. The segmentation of each planes allows redundant studies of the trigger efficiency and provides a rough tracking of particles.

The sensitive area of the two S1 layers is 33×40.8 cm2. with the first layer divided into 8 bars and the second layer divided into 6 bars. The total sensitive area of the S2 and S3 planes is 15×180 cm2 segmented into 2×2 and 3×3 bars, respectively. The S1 and S3 layers, placed on the top of the instrument and between the spectrometer and the calorimeter, respectively, are 7 mm thick, while the S2 layers, located just above the anticoincidence placed over the magnet, are 5 mm thick.