150 fig2 is a circuit diagram of an equivalent circuit 200 of the electron multiplier 107 combined with the bias circuit on the bias circuit board 130 in fig1 the equivalent circuit 200 includes a cathode node 202 an emitter node 204 and an anode node 206 the cylindrical channel body 108 in fig1 is represented by a channel circuit 210 between the cathode 122 and the emitter 124 in fig1 the channel circuit 210 has the electrical impedance equivalent of a channel resistance 212 and a channel capacitance 214 representing the capacitance between the cathode node 202 and the emitter node 204 a capacitance represented by the capacitor 220 is created between the emitter node 204 and the anode node 206 by the close proximity of these two conductors an emitter current 222 is the gain amplified electron current measured by the electrometer as will be explained below any bias circuit connected to the emitter node 204 must be able to maintain a constant potential on the emitter node 204 regardless of currents entering the emitter node 204 from the channel circuit 210 or the capacitance 220 in addition to emitter current 222 fig3 is a circuit diagram of the compensation circuit 300 that is connected to the electron multiplier 107 from fig1 as explained above the components of the compensation circuit 300 are mounted on the bias circuit board 130 in fig1 like elements are labeled with identical element.