Electron channeltron multiplier

Figure 6. Diagram of our 1-atm ion mobility spectrometer (IMS) apparatus (a) stainless steel source gas dilution volume, (b) septum inlet, (c) needle valve, (d) Nj source gas supply, (e) source and drift gas exhaust, (f) flow meter, (g) pressure transducer, (h) insulated box, (i) drift tube, (j) ion source, (k) Bradbury-Nielson gate, (I) Faraday plate/MS aperture, (m) drift gas inlet, (n) universal joint, (o) electrostatic lens element, (p) quadrupole mass filter, (q) 6"-diffusion pump, (r) first vacuum envelope, (s) channeltron electron multiplier, (t) second vacuum envelope, (u) 3"-dif-fusion pump, (v) Nj drift gas, (w) leak valve, (x) on/off valves, (y) fused silica capillary, (z) 4-liter stainless steel dilution volume, (aa) Nj gas supply.

The energy analysis of these inelastically scattered electrons is carried out by a cylindrical sector identical to the monochromator. The electrons are finally detected by a channeltron electron multiplier and the signal is amplified, counted and recorded outside of the vacuum chamber. A typical specularly reflected beam has an intensity of 10 to 10 electrons per second in the elastic channel and a full width at half maximum between 7 and 10 meV (60-80 cm l 1 meV = 8.065 cm-- -). Scattering into inelastic channels is between 10 and 1000 electrons per second. In our case the spectrometer is rotatable so that possible angular effects can also be studied. This becomes important for the study of vibrational excitation by short range "impact" scattering (8, 9, 10). 

The names of both detectors reflect that these devices are channels which act as continuous dynode electron multipliers. If there is one channel, it is called a channeltron (channeltron electron multiplier, CEM), if many microchannels are used to form a plate it is called a microchannel electron multiplier plate (in short a microchannelplate, MCP, or channelplate), see Fig. 4.17. A comprehensive description of these devices is given in [Wiz79]. 

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.

Renard and Deloche [261] examined the surface diffusion of physi-sorbed tritium on a single crystal Ni lll] surface. The gas was deposited as a patch with the crystal held at 4K and the concentration profile across the surface was determined by collection of the radiation emitted from tritium in a channeltron electron multiplier. For the diffusion experiments, the collector was positioned so as to collect radiation from a point well outside the original patch area and the sample was then heated to temperatures in the range 13—20 K. Desorption was also appreciable from, the physisorbed layer and so they derived the coverage-time relation (at fixed temperature)... 

Two of the three laser ionization methods have already been discussed, namely one-photon PI and multiphoton MPI. The third type is resonance enhanced MPI, or REMPI. In the latter method the laser is tuned so that an intermediate state of the molecule is excited with one, two, or perhaps three photons. The excitation of the intermediate state determines the overall cross section for the process because the absorption of additional photons to reach the ionization continuum is generally rapid. In contrast to PI and MPI, REMPI is state selective if the absorption process is resonant between two bound and reasonably long-lived states of the molecule. It is an extremely sensitive method for product detection because the result of the REMPI process is an ion which can be detected with near 100% efficiency. Not only is the ion collection efficiency of the detector (e.g., by channeltron electron multiplier or a multichannel plate detector) extremely high (ca. 50%), but all ions regardless of their initial velocity vector can be collected by the application of appropriate electric fields. This is a major advantage... 

The detectors used for charged particles are channeltron electron multipliers (CEM) which produce fast (10 ns) pulses with approximately 90% absolute detection efficiency for electrons and nearly 100% efficiency for... 

The linear dynamic range of calibration is about six orders of magnitude, comparable to ICP-AES. The upper limit is generally determined by the ability of the Channeltron electron multiplier to handle intense ion beams. Analyte concentrations of 1 mg/liter typically produce 1 X 10 counts/sec, an indication of the upper limit [43). 

Ionization takes place in the RC that contains a LC ion source, which consists of a LC ion emitter and repeller. The primary LC ions ionize the target sample species by adduct formation to give [M + Li]+ by termolecular association reactions. The adduct ions are focused by ion lens and transferred to the QMS chamber. A QMS is often employed, and detection is by a channeltron electron multiplier detector. Other mass spectrometers can be used. 

Channeltron , Electron Multiplier Handbook for Mass Spectrometry Applications, Galileo Electro-Optic Corp., 1991. (Channeltron is a registered trademark of Galileo Corp.)... 

After the ions have been extracted from the plasma, they are conducted into a quadrupole mass analyzer (fig. 18). This is an array of four metal rods biased at carefully regulated DC and RF voltages. The voltages are selected so that ions of a given mass-to-charge ratio (m/z) have a stable path through the rod structure while other ions are deflected into the rods and are thus removed from the beam (Dawson 1976). The selected ions leave the mass analyzer and strike a detector, usually a Channeltron electron multiplier (Kurz 1979) operated in a pulse counting mode. In this fashion, discrete pulses from individual ions can be observed. The multiplier is offset and the optical axis is screened with a baffle to prevent detection of photons from the ICP. 

Fig. 18. Diagram of an ICP-MS device. A, torch and load coil B, grounded center tap C, grounded shielding box D, sampler E, line to rotary vacuum pump F, skimmer G, grounded metal disk H, ion lens I, Bessel box with photon stop in center (J) K, RF-only quadrupole rods L, quadrupole mass analyzer M, exit ion lens and ion deflector N, Channeltron electron multiplier P, cryogenic baffles for evacuation. Reproduced with permission (Houk and Thompson 1988).

Fig. 5.2. SCIEX ELAN ICP-MS device. A = ICP B = load coil grounded at center, C = shielding box, D = sampler, E = mechanical vacuum pump, F = skimmer, G = grounded metal stop, H = ion lenses, I = Bessel box, J = photon stop, K = RF only quadrupole rods, L = quadrupole mass analyzer, M = ion lenses and deflector, N - Channeltron electron multiplier, P = cryoshells. Reproduced from Mass Spectram. Reviews with permission of John Wiley.

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