Positrons, or electrons at reversed magnetic field polarity, can also be detected, although the range of angles is lower in this case.
Fig. 18 shows
the mean number of detected photoelectrons for 1.8 GeV
as a function of the segment number.
Only about
of all segments are active.
This is due to the strong magnetic field at small angles bending
positrons away from the beam axis.
Fig. 19 shows the same value as a function of angles Theta
and Phi. It can be seen that the
detection efficiency near the middle-plane
is smaller for
than for
,
however most of the remaining region has reasonable
detection efficiencies for
.