Ion Detectors
Channeltron
A channeltron is a horn-shaped continuous dynode structure that is coated
on the inside with a electron emissive material. An ion striking the channeltron
creates secondary electrons that have an avalanche effect to create more
secondary electrons and finally a current pulse.
Daly detector
A Daly detector consists of a metal knob that emits secondary electrons
when struck by an ion. The secondary electrons are accelerated onto a scintillator
that produces light that is then detected by a photomultiplier tube.
Electron multiplier tube (EMT)
Electron multiplier tubes are similar in design to photomultiplier tubes.
They consist of a series of biased dynodes that eject secondary electrons
when they are struck by an ion. They therefore multiply the ion current
and can be used in analog or digital mode.
Faraday cup
A Faraday cup is a metal cup that is placed in the path of the ion beam.
It is attached to an electrometer, which measures the ion-beam current.
Since a Faraday cup can only be used in an analog mode it is less sensitive
than other detectors that are capable of operating in pulse-counting mode.
Microchannel plate
A microchannel plate consists of an array of glass capillaries (10-25 um
inner diameter) that are coated on the inside with a electron-emissive
material. The capillaries are biased at a high voltage and like the channeltron,
an ion that strikes the inside wall one of the capillaries creates an avalanche
of secondary electrons. This cascading effect creates a gain of 103
to 104 and produces a current pulse at the output.
Schematic of a microchannel plate
Microchannel plates (MCP) are also used as an intensifier for low-intensity
light detection with array detectors.
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