Channel electron multipliers CEM

Channel electron multipliers (CEM) are fabricated from lead-silica glass (Fig. 1.32) and can have curved or straight forms. In a channel electron multiplier, when the charged particles (positive or negative) hit the surface of the electrode, electrons are produced from the surface which then generate the current. 

Fig. 1.32 Straight channel electron multipliers (CEM) are typically used in quadrupole-type mass spectrometers.

Figure 4.5 Channel electron multiplier (CEM) working in the analogue and pulse-counting mode. (Reproduced by permission of GV Instruments Ltd.)...

Pendyala et al. [24] found that the efficiency of single-channel electron multipliers (CEMs) (also called channeltrons or spiraltrons) was about the same for positrons and electrons of the same incident energy. 

Figure 1. TPEsCO apparatus using two-channel electron multiplier (CEM) electron detectors. Potentials on the several lens elements and deflectors are tuned manually for optimum electron pair detection and resolution.

Figure 9.27 (a) A schematic channel electron multiplier (CEM), consisting of a glass or interior-... 

After the ions have been separated by the analyser, they will be focused onto the detector, where they are converted into a measurable electrical current. This results in a signal in the form of a series of peaks showing the abundance of those particular ions. The most common type of detector is an electron multiplier, which exists in two forms the discrete dynode electron multiplier and the continuous dynode electron multiplier (also called a channel electron multiplier [CEM]). 

Another common version of the SEM is a horn-shaped assembly, popularly known as a channel electron multiplier (CEM) or continuous-dynode EM... 

Most of the disadvantages of discrete dynode SEMs are overcome by the development of channel electron multipliers (CEMs) (sometimes also referred to as continuous dynode electron multipliers, CDEMs) that are by far the most widely used ion detectors in analytical mass spectrometers. 

Because fluorescence detection by repeated absorption-emission cycles is not applicable to trapped molecular ions in UHV, that is, in the absence of collisions with a buffer gas [68], different techniques are required for their reliable identification. A commonly used destructive technique for molecular ions is time-of-flight (TOP) mass spectroscopy. We have used a simplified variant in the Ba+ apparatus. The trapped ions are extracted from the trap by reducing the radio-frequency amplitude, in the presence of a finite dc quadrupole potential Vo, which causes the ion trajectories to become unstable (the Mathieu -parameter enters the instability region). Heavy and hot ions escape first. Upon leaving the trap, the ions are guided to and attracted by the cathode of a channel electron multiplier (CEM) and counted. 

Channel Electron Multiplier (CEM) or channeltron is an electron detector that is used to multiply each electron (up to 10 times) to provide a pulse output suitable for further amplification by conventional electronic circuits. This is a bent tube that is coated with a photoelectric material (of a specific work function) with a high secondary electron coefficient. The tube is kept at a potential of about 2.5 kV. When the electrons pass through the inlet aperture of the CEM and strike the surface of the CEM, a collision of sufficient energy between the ultraviolet radiation and the CEM wall will eject at least one electron. When an electron strikes the mouth of the tube, a number of secondaries is produced that is accelerated in the channeltron. A local electric field created by the bias voltage of the power source accelerates these... 

Advances in the measurement technics in the last 15 years especially the development of channel electron multipliers (CEM s) render now the possibility to detect besides electrons (or in general negative particles) also positive ions. Dickinson et al. [12-22 3 examined particle emissions and corresponding emissions of photons, radio-waves and accustic waves accompanying macroscopic fractui e... 

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