Detectors channel electron multiplier

The most connnon detectors used for TOF-SARS are continuous dynode channel electron multipliers which... 

Soft X-ray absorption measurements are done at low-energy synchrotron X-ray facilities such as the UV ring at NSLS or the Advanced Photon Source (APS) at Lawrence Berkeley National Laboratory (LBNL). The beam size is typically 1 mm in diameter. The electron yield data are usually obtained in the total electron yield (EY) mode, measuring the current from a channel electron multiplier (Channeltron). Sometimes a voltage bias is applied to increase surface sensitivity. This is referred to as the partial electron yield (PEY) mode. Huorescence yield (EY) data are recorded using a windowless energy dispersive Si (Li) detector. The experiments are conducted in vacuum at a pressure of 2 X 10 torr. 

The analyser will always be preceded by some form of collection optics, and followed by an ion detector (usually a channel electron multiplier which converts ions into electron showers). There are three types of analyser for use in SIMS spectrometers, the magnetic sector instrument, the quadrupole analyser and time-of -flight (TOF) systems. 

The lifetime of channel electron multipliers is ca. 1-2 years. Neutrals or photons hitting the detector also increase the noise of the detection. 

Another limit source of uncertainty in isotope ratio measurements by mass spectrometry is the dead time of the ion detector for counting rates higher than 106cps, because a lower number of counts are usually registered than actually occur. Dead time correction of the detector is required if extreme isotope ratios are measured by channel electron multipliers and pulsed counting systems.86... 

The ideal high-throughput analytical technique would be efficient in terms of required resources and would be scalable to accommodate an arbitrarily large number of samples. In addition, this scalability would be such that the dependence of the cost of the equipment to perform the experiments would scale in a less than linear manner as a function of the number of samples that could be studied. The only way to accomplish this is to have one or more aspects of the experimental setup utilize an array-based approach. Array detectors are massively multiplexed versions of single-element detectors composed of a rectangular grid of small detectors. The most commonly encountered examples are CCD cameras, which are used to acquire ultraviolet, visible and near-infrared (IR) photons in a parallel manner. Other examples include IR focal plane arrays (FPAs) for the collection of IR photons and channel electron multipliers for the collection of electrons. 

Fig. 2 Portion of the collinear laser-ion beam apparatus. QDl, QD2, electrostatic quadrupole deflectors CEM, channel electron multiplier DP, deflection plates PD, positive ion detector FC, Faraday cup ND, neutral particle detector CG, conducting glass plate AP, aperture MP, metal plate A, any element. The distance between QDl and QD2 is approximately 0.5 m.

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.

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A channel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl. 23.4. The sample has to be rotated to measure ion scattering... 

Figure 14.4 Schematic diagram of an ESCA instmment with a single channel electron multiplier detector.

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