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Single Ion Detection with Microchannel Plate
Microchannel plate amplify initial electron emission event, produced by different kind of particles such as ions, electrons, clusters, alpha particles, positrons, UV photons, EUV photons, soft-Xray, X ray etc...
Single electron event results in electron cloud of about 104 electrons in single MCP assemblies, 106 electrons in double (chevron) MCP assemblies and 107-108 in triple (Z-stack MCP assemblies).
Let's estimate a signal generated by an electron cloud on the oscilloscope.
Total charge produced in single electron event is equal to Q = e*n, when e is an electron charge e=1.6*10-19 C and and n is a number of electrons in electron cloud. Current generated by electron cloud can be estimated as I = Q/t, where t is a duration of electron cloud pulse. t depends on readout anode and registration electronics and can be anywhere from 0.2ns (collection time of electron cloud on metal anode) to 10 ns and more if slow registration electronics is used. For an estimate let's take t=1ns
Voltage generated by electron cloud current on resistance R is equal to V = I*R = e*n*R/t. For R=50 Ohm we have:
| Number of MCPs | Single electron signal, t=1ns | Single electron signal, t=10ns |
| 1 | 80 mV | 8 mV |
| 2 | 8mV | 0.8mV |
| 3 | >0.8V | >0.08V |
Typically, single and double MCP assemblies would require a preamplifier for reliable detection of single electron events.
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