help on electron detection

[philosophus]

I'm working on a research topic that involves detection of secondary
electrons induced by energetic ions. Secondary electron emission may
originate from the substrate from which ions emerge, or ions may be forced
to pass through a thin carbon foil (thin enough not to generate too much
straggling and cause loss of resolution) and secondary electrons are emitted
from the foil.

The problem is the detection of electrons... The ions and electrons are
separated by a crossed electric/magnetic filter: energetic ions travel
straight to the ion detector and electrons are steered in the magnetic field
onto the electron detector. The electron detector is a chevron microchannel
plate (MCP). A time-of-flight spectrum is obtained when the signals from the
two detectors are run in coincidence.

Although sounds rather straightforward, I've had difficulties for a long
time with detection of electrons. I can get a reasonable electron count on
the electron MCP; but when I run the two detectors in coincidence, I either
get no spectrum, or a spectrum with spurious peaks. Most of time, the peaks
do not make physical sense due to the geometry of the time-of-flight
telescope.

If anyone has any past experience on this kind of a problem, I'd greatly
appreciate comments.

Thanks,

Phylosophus