Forward–backward correlated secondary-electron emission depending on the angle of emergence of protons transmitted through a thin carbon foil

The statistical distributions of the secondary electrons (SEs) emitted forward and backward from a thin carbon foil have been measured simultaneously, in coincidence with foil-transmitted protons of 1.0 and 2.5 MeV, as a function of the angle of emergence, θem, of the protons. Irrespective of the incident energy, the measured SE yields increase with increasing angle of emergence in both the forward and the backward directions. As for the forward–backward correlation of the SE emission, the forward- and backward-emitted SE yields induced by 2.5 MeV protons increase gradually with increasing number of SEs emitted in the opposite directions. This positive correlation becomes slightly more pronounced with increasing angle of emergence. On the other hand, for 1.0 MeV, a positive correlation observed at θem = 0 mrad changes to a negative one at θem = 1.0 and 2.0 mrad.