Detector secondary electron multiplier

Photocells and photomultipliers (secondary electron multipliers, SEM) are mainly employed in photometry. These are detectors with an external photo-effect . 

Once they have left the separation system the ions will meet the ion trap or detector which, in the simplest instance, will be in the form of a Faraday cage (Faraday cup). In any case the ions which impinge on the detector will be neutralized by electrons from the ion trap. Shown, after electrical amplification, as the measurement signal itself is the corresponding ion emission stream . To achieve greater sensitivity, a secondary electron multiplier pickup (SEMP) can be employed in place of the Faraday cup. 

We should not forget that an appropriate detector, a Faraday cup or a secondary electron multiplier equipped with a conversion dynode, is needed for ion detection. Most commercial instruments are equipped with a secondary electron multiplier, which can be operated in a low amplification mode, the analogue mode, and with a high gain, the counting mode, where each ion is counted. With this dual mode, a linear dynamic range of up to nine orders of magnitude can be achieved, so that major and minor components of the sample can be measured in one run. 

Figure 1. Experimental set-up for performing transient two-photon ionization spectroscopy on metal clusters. The particles were produced in a seeded beam expansion, their flux detected with a Langmuir-Taylor detector (LTD). The pump and probe laser pulses excited and ionized the beam particles. The photoions were size selectively recorded in a quadrupole mass spectrometer (QMS) and detected with a secondary electron multiplier (SEM). The signals were then recorded as a function of delay between pump and probe pulse.

Continuous dynode electron multipliers (such as the Channeltron) are horn-shaped detectors (Fig. 3.14b). A high voltage is applied between the input and output ends of the detector. When an ion strikes the detector, secondary electrons are produced. These electrons in turn strike the wall of the detector, generating more electrons. Up to 108 electrons are produced and collected at a collector electrode at the output end of the detector for each incident ion, depending on the applied voltage. 

Regelous et al have reported ou the use of the isotope dilutiou techuique (using a Pa spike with a half-life of 26.97 days) for the quantitative measurement of 20 fg of protactinium in silicate rocks after chemical separation of the actinide from the rock matrix by MC-ICP-MS (Neptune, Thermo Fisher Scientific, Bremen - equipped with uiue Faraday detectors, oue secondary electron multiplier and a retarding potential quadrupole for high abundance sensitivity measurements). 

Photocells and photomultipliers (secondary electron multipliers, SEM) are mainly i are detectors with an external photo-effect .-------------------------------... 

As shown in the right side of Fig. 9, a quadrupole mass spectrometer, MSG 300, with a gas-tight ion source, secondary electron multiplier, direction detector, and a turbo-molecular pump (TURBOVAC 150) is equipped with a membrane inlet (all from Nippon Shinku, Tokyo). The resolution scale is 300. Mass spectrometry can also be used for the measurement of dissolved gases in a liquid phase using a steam sterilizable membrane probe. Recently, the application of the mass spectrometer to fermentation processes has increased markedly. 

Most process analyzers utilize either a Faraday cup or a secondary electron multiplier (SEM) for detection. The Faraday cup is the simpler and more mgged and stable of the two, but is generally useful for detection of species at higher concentrations (100 ppm to 100%). The SEM is much more sensitive, capable of measurements in the ppb range. It is quite common to configure a process MS with both detectors, along with a set of electrostatic lenses to switch the mass-filtered ion beam between the two detectors. This results in a single process analyzer that is capable of quantitation from 1 ppb to 100 % ... 

Secondary electron multiplier (SEM) detectors replaced Faraday cup detectors for scanning mass spectrometers. The electron multiplier is based on the concept of a photomultiplier except that there is no glass membrane, so ions (electrons) can enter the amplification region of the detector. Because electron multipliers are not sealed and are open to the atmosphere, they must be operated under vacuum conditions and therefore cannot be used directly in atmospheric pressure IMS. 

The exit radiation is measured in a secondary electron multiplier (SEM) used as a detector as the photons hit the photocathode. The latter usually consists of alkali-metal alloys, and is of varying sensitivity, depending... 

The secondary electron multiplier (SEM) detector is the key to the role of mass spectrometry as an extremely sensitive analytical technique with wide dynamic range and compatibility with on-line coupling to fast chromatographic separations. The SEM was a natural development from the invention of the photomultiplier (Zworkin 1936, 1939), in which photoelectrons produced by photons falling on a conversion dynode with a photo-sensitive surface are amplified in an avalanche fashion by accelerating the original (first strike) photoelectrons on to a... 

The most common detector today is the secondary electron multiplier, which amplifies the... 

Fig. 2.2. Experimental setup (as used for the investigations on NasB). An argon ion laser (ps mode-locked fs all lines, visible) pumps either a femtosecond laser system (a) (OPO synchronously pumped optical parametric oscillator SHG second-harmonic generator) or a picosecond laser system (b) (taken from [178]). The pulse duration and spectral width of the laser pulses are measured by an autocorrelator (A) and a spectrometer (S) respectively. A Michelson arrangement allows the probe pulses to be delayed At) with respect to the pump pulses. A quadrupole mass filter (QMS) enables the selection of the ensemble of investigated molecules ionized by a pump probe cycle. A secondary electron multiplier (SEM) detects the intensity I of the ions as a function of the delay time At. A Langmuir-Taylor detector (LTD) measures the total intensity /o of the cluster beam. The ratio I/Iq as a function of the delay time At is called the real-time spectrum...

Fig. 2.18. Side elevation of the molecular beam machine s two-chamber setup. Chi vacuum chamber to generate the molecular beam by adiabatic expansion. A seeded supersonic beam source is placed here. Further details are shown in Fig. 2.19. Ch2 here, the molecules interact with the laser pulses. Detection is performed by a quadrupole mass spectrometer (QMS) with a 90° ion deflector between the mass filter and secondary electron multiplier (SEM) (Fig. 2.20) or the Langmuir-Taylor detector (Fig. 2.22)...

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