Ion Detectors


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.

Related topics

Further Information

/chem-ed/ms/detector/detector.htm, updated 2/1/97

Copyright © 1996 by Brian M. Tissue, all rights reserved.

Science Hypermedia Home Page