/diy/ - Do It Yourself

I want to quantitatively measure electric charge building up on a metal surface from impacting ions/ionising radiation, how do? I assume that using a capacitor to ground (whatever ground is in this context) and measuring the voltage across it is some way of measuring the surface's charge.

Ideally I'd use something similar to a Kolbe electroscope, since it measures absolute charge instead of relative charge and lets essentially no current through, though I'm not sure how it stores its energy. Capacitance to the atmosphere? Or is it all potential energy of the needle?

For a solid state method I assume I'd need a very high input impedance and perhaps some way of measuring a log scale to have a similar relative accuracy at low and high voltages, since I could be measuring the charge building up over a few hours at a time. Perhaps pic related? If changing the capacitance changes the voltage at the FET gate through V=Q/C, will that also change the electric field emitted by the surface and potentially deter more ions from impacting differently? I can't see how that would happen since the device's net charge will be the same, leading back to the question of what the voltage is relative to.