MCD Detector

Channel electron multipliers with an extended dynamic range for extremely high count rate applications are used as standard. This device is a specially formed and treated glass tube which has the effect of multiplying a single electron at the input to a pulse of around 10⁸ electrons at the output. Because of their low resistance, the extended range CEMs are suitable for extremely high count rates. A voltage between 2.5 - 3.5 kV across the cone and the tail-end initiates the electron multiplication. Electron multiplication is produced by the emissive layer along the inner surface of the channel. The gain is governed by the detector voltage and the condition of the emissive layer. Upgrades from single to multi channel detection can be performed on-site.

Multichannel detection is performed by appropriately arranging 5 or 9 CEMs as collectors in the exit plane. The number of particles arriving at each collector is counted separately, and these numbers are stored and preprocessed in the data acquisition unit.

By sweeping the spectrometer voltage, the electron path is moved across each collector channel step by step. In this way, each collector records a complete spectrum, with a fixed energy offset between neighboring channels. In principle, by sweeping the spectrum once over the detector area, five or nine parallel spectra are recorded simultaneously. As the kinetic energy of the particles arriving at each collector is known, the number of particles from each channel can be summed to obtain the total number of particles for each kinetic energy.