Discrete Dynode Electron Multipliers

Figure 2.21. Schematic of (a) a photoplate detector (b) a Faraday cup (c) a discrete-dynode electron multiplier (EM) of Venetian blind type and (d) a continuous dynode EM. Parts (c) and (d) reprinted from A. Westman-Brinkmalm and G. Brinkmalm (2002). In Mass Spectrometry and Hyphenated Techniques in Neuropeptide Research, J. Silberring and R. Ekman (eds.) New York John Wiley Sons, 47-105. With permission of John Wiley Sons, Inc.

In many applications, discrete dynode electron multipliers have been replaced by a less costly continuous dynode design. These conicalshaped devices (Fig. 11.14) are fabricated from resistive glass (doped... 

Fig. 4.57. Discrete dynode electron multipliers, (a) Schematic of a 14-stage SEM. (b) Photograph of an old-fashioned 16-stage Venetian blind-type SEM clearly showing the resistors and ceramics insulators between the stacking dynodes at its side, (a) Adapted from Ref. [238] by permission. Springer-Verlag Heidelberg, 1991.

Fig. 1.31 Discrete-dynode electron multiplier. When the ions hit the surface of the detector electrons are emitted to form an avalanche of electrons which generates the signal.

Figure 14 Detectors (a) Discrete dynode electron multiplier, (b) Dual-mode discrete dynode electron multiplier detector, (c) Channeltron electron multiplier, (d) Faraday collector. (f) Daly detector.

Figure 7-12 presents a conceptual diagram of the operation of a discrete dynode electron multiplier. When an ion strikes the first dynode, it causes the ejection of one or more electrons ( secondary electrons ) from the dynode surface. The electron is accelerated toward the second dynode by a voltage difference of -100 V. Upon strildng the second dynode, this electron causes the ejection of additional electrons, typically 2 or 3 in number. The second group of electrons is then accelerated toward the third d)mode, and upon strildng the third dynode, causes the ejection of several more electrons, The process is repeated through a chain of dynodes, num-... 

Figure 7-12 Discrete dynode electron multiplier showing dynode structure and generation of electron cascade.

The most common transducers for ICP-MS are electron multipliers. The discrete dynode electron multiplier operates much like the photomultiplier transducer for ultraviolet/visible radiation, discussed in Section 25A-4. Electrons strike a cathode, where secondary electrons are emitted. These are attracted to dynodes that are each held at a successively higher positive voltage. Electron multipliers with up to 20 dynodes are available. These devices can multiply the signal strength by a factor of up to 10. ... 

Figure 9.26 (a) A schematic discrete-dynode electron multiplier, showing the electron gain at... 

Diagram a discrete-dynode electron multiplier and describe its operation. Diagram a CEM and describe its operation. 

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]). 

In the discrete dynode electron multiplier, the ions from the analyser are converted into electrons by a dynode (an electron used to provide secondary emission). The dynode surface is typically composed of CsSb, BeO, or GaP, which are secondary emitting materials. This means that the electrons are emitted or released from atoms in the surface layer with the number of electrons released depending upon... 

FIGURE 7.7 Discrete-dynode electron multiplier. (From Babis et al.. Performance evaluation of a miniature ion mobility spectrometer drift cell for application in handheld explosives detection ion mobility spectrometers, Anal. Bioanal. Chem. 2009, 395, 411-419. With permission.)... 

A different kind of discrete dynode electron multiplier detector using an off-axis conversion dynode is exem-phfied by the Daly detector (Daly 1960), developed in response to reduced hfetimes of conventional discrete... 

Figure 1 l-2a is a schematic of a discrete-dynode electron multiplier designed for collecting and converting positive ions into an electrical signal. This device is... 

FIQURE 11 >2 (a) Discrete-dynode electron multiplier. Oynodes are kept at successively higher voltages via a multistage voltage divider (b) Continuous-dynode electron multiplier. (Adapted from J. T. Watson. Introduction to Mass Spectrometry, 3rd ed., pp. 334-35, New York Raven Press, 1997. With permission.)... 

Figure 4.17 Schematic illustrations of (a) a Discrete Dynode Electron Multiplier, (b) a Channeltron, and (c) a Micro-Channel Plate, along with the electron cascades generated when these detectors are biased. Reprinted with permission from van der Heide (2012) Copyright 2012 John Wiley and Sons.

Figure 4.18 Schematic example of Pulse Height Distribution analysis carried out for 4500 eV secondary ions impinging on an ETP Discrete Dynode Electron Multiplier operated at the listed voltages. Pulse counting was carried out using custom built ECL logic pre-amplifier/discriminator units. Discriminator voltage in this case should be set at 5 mV. Reproduced with permission from van der Heide and Fichter (1998) Copyright 1998 John Wiley and Sons.

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