Daly multiplier

A scintillator, sometimes known as the Daly detector, is an ion collector that is especially useful for studies on metastable ions. The principle of operation is illustrated in Figure 28.4. As with the first dynode of an electron multiplier, the arrival of a fast ion causes electrons to be emitted, and they are accelerated toward a second dynode. In this case, the dynode consists of a substance (a scintillator) that emits photons (light). The emitted light is detected by a commercial photon... 

As with mass analyzers, many types of mass detectors equipped with an electron multiplier are available. Most common mass detectors are the chan-neltron, Daly detector, electron multiplier tubes, and the Faraday cup. All generate a current when charged analytes generated in the source and separated in the analyzer impinge on them. This current is recorded as a function of the masses selected by the electrical-field settings. 

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.

The electro-optical ion detector (EOID) combines ion and photon detection devices. This type of detector operates by converting ions to electrons and then to photons. The most common electro-optical ion detector is called the Daly detector. As shown in Figure 3.7, this type of detector is made up of two conversion dynodes, a scintillation or phosphorescent screen and a photomultiplier. This device allows the detection of both positive and negative ions. As for the electron multipliers, ions from the analyser strike a dynode. In the positive mode, ions are accelerated towards the dynode that carries a negative potential, whereas in the negative mode, ions are accelerated towards the positive dynode. Secondary electrons... 

The Daly detector uses a photomultiplier rather than an electron multiplier. Ions leaving the analyzer are directed onto a conversion dynode, and the ejected electrons are accelerated onto a plate coated with a fast-acting scintillant. Each electron releases a photon from the scintillant. The photons then enter a photomultiplier tube and impact on a photocathode, producing electrons (photoelectric effect) and initiating an electron cascade (Pigure 2.40). The output from the photomultiplier is further amplified electronically, similarly to the output of dynode type electron multipliers. The level of amplification is similar to that of electron multipliers. Photomultiplier tubes last longer than electron multipliers, but the scintillant-coated plates require replacement every few years. 

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... 

A) Venetian blind multiplier B) Box and grid multiplier C) Channeltron multiplier D) Microchannelplates E) Daly detector ... 

The use of a triple filament source (instead of a single) because it is much freer from mass discrimination (Palmer, 1956, in Wilson and Daly, 1963) and because its potential for higher sensitivity may obviate the necessity for an electron multiplier detector instead of a Faraday-cup (Inghram and Chupka, 1953). 

With no stable isotope pair within the U system or a suitable AME, a standard-sample bracketing protocol is usually employed to correct for mass bias. Human urine generally contains very low concentrations of U (generally 1-5 ng/L), so an isotope dilution strategy is required, together with ion-counting detection (ideally a Daly photomultiplier or discrete dynode secondary electron multiplier) and a multi-static (rather than multi-dynamic) peak-jumping routine, for precise measurement of the total U concentration and the minor isotopes of and even... 

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