electronmultiplier

An electron multiplier is a vacuum-based device that amplifies electronic signals by exploiting secondary emission. It typically uses a cascade of surfaces—dynodes or microchannels—where incident electrons trigger the emission of additional electrons. A single stage multiplies electrons by a secondary emission factor δ; in a multistage stack with n stages, the overall gain is approximately δ^n, enabling detection of single- or few-electron events. Configurations include dynode chain devices used in photomultiplier tubes, channel electron multipliers (CEMs), and microchannel plates (MCPs).

Construction and operation: The device is housed in a sealed vacuum envelope. A primary electron source—such as a photocathode or ionization event—provides electrons that enter the multiplier. A high voltage is applied across the stages, accelerating electrons toward subsequent dynodes or channels and inducing secondary emission at each encounter. Gains typically range from about 10^3 to 10^8, with MCPs offering very fast timing (tens of picoseconds to nanoseconds) and high spatial resolution when tiled in arrays. Performance depends on materials, surface quality, and aging, since secondary emission yields can degrade with use.

Applications: Electron multipliers are used to detect low-intensity light in photomultiplier tubes, in mass spectrometry and ion/electron spectroscopy, X-ray detectors, particle physics experiments, and radiation dosimetry. They are valued for high sensitivity, fast response, and wide dynamic range, but require stable high-voltage operation and can be affected by magnetic fields and long-term aging.