Multiple ion counting

Figure 9. Schematic diagram showing a second-generation MC-ICPMS instrament (ThermoFinnigan Neptune). This instrument utilizes double-focusing and is equipped with a motorized multiple-Faraday collector block with two channels that can be operated in high-resolution mode. Optional multiple-ion counting channels are also available for the simultaneous measurement of low-intensity ion beams. [Used with permission of Thermo Finnigan.]...

In 1977, Jochum et aZ.12,14 developed the multiple ion counting (MC) technique using an old spark source mass spectrometer with 20 separate channeltrons 1.8 mm wide for simultaneous electrical ion detection. The sensitivity was increased by a factor of 20 compared to SSMS with ion detection using a photoplate and the precision of the analytical results was improved. 

In 1977, Jochum et developed the multiple ion counting (MC) technique using an old... 

Jakopic R, Richter S, Kuehn H, Aregbe Y (2008) Isotope ratio measurements of pg-size plutonium samples using TIMS in combination with the Multiple Ion Counting and filament carburization, INIS-FR-09-0127. In Atalante 2008 nuclear fuel cycle for a sustainable future, Montpellier, France, 19-23 May... 

Taylor, R.N., Wameke, T., Milton, J.A., Croudace, I.W., Warwick, P.E., and Nesbitt, R.W. (2003) Multiple ion counting determination of plutonium isotope ratios using multi-collector ICPMS, J. Anal. At. Spectrom., 18, 480-484. 

Hartlaub, R.P., Greaser, R.A., MacHattie, T.G., and Bohm, C. (2005) U-Pb zircon dating by laser ablation-MC-ICP-MS using a new multiple ion counting Faraday collector array. 

Figure 6. Schematic outline of the first commercially available multiple collector ICPMS, the Plasma 54, after Halhday et al. (1995). This instrument uses Nier-Johnson double-focusing and is equipped with eight independently adjustable Faraday collectors. The axial collector can be wound down to provide access to a Daly detector equipped with ion counting capabilities and a second-stage energy filter for high abundance sensitivity measurements. The sample may be introduced to the plasma source by either solution aspiration or laser ablation.

Multiple-collection techniques. Uranium. Table 1 shows a typical protocol used by multi-collector instruments (equipped with one ion counting channel) both in MC-TIMS, MC-ICPMS and LA-MC-ICPMS (e.g., Cohen et al. 1992 Stirling et al. 1995 Luo et al. 1997 Stirling et al. 2000 Pietruszka et al. 2002). A first sequence monitors the atomic ratios between and by aligning Faraday collectors for masses (10 ... 

Two additional points that are self-evident are discussed below for the sake of completeness. The coordination number of a metal ion counting all ligands other than the adjacent metal involved in multiple metal bonding is less than the maximum coordination number possible for that metal center. Furthermore, the number of d-electrons on the metal is nearly equal to the number of metal valence orbitals not involved in metal-ligand bonding to optimize metal-metal bond formation by filled bonding MOs. 

TIMS analysis was performed on a fully automated VG Sector 54 mass spectrometer with eight adjustable faraday cups and a Daly ion-counting photomultiplier system. Analysis was performed in static mode. Each sample was analyzed 50 times to ensure acceptable precision. The TIMS analysis was standardized by use of the NIST SRM981 common lead standard. Multiple analyses of the SRM981 standard were used to determine a fractionation correction of 0.12% per amu and an overall error 0.06% per amu. Errors between runs of the same sample were below 0.01% per amu. This level of precision is comparable to the archaeometry database for lead isotopes (8). 

Perhaps the most interesting application of electron-electron covariance mapping relates to the question of the major mode of multiple ionization of atoms and molecules. Luk et al. [34] studied the multiple ionization process in Xe using a laser of 193 nm wavelength and 10 ps pulse length and conventional ion TOP spectroscopy they suggested that it was direct (a collective, instantaneous emission of many electrons). Lambropoulos [35] pointed out that, with a laser of such modest rise time, the ionization must proceed sequentially. In fact L Huillier et al. [36] had also studied Xe at 532 nm and observed a knee in the curve of log (ion counts) vs log (laser intensity) for Xe that they attributed to direct double ionization. 

Modern TIMS instruments are equipped with multiple ion detectors (see Fig. 17.15). In the 1980s, Faraday cup arrays became commercially available, and these provided significant improvements in isotopic precision and sample utilization. In the 1990s, arrays of pulse counting ion detectors with very compact EM... 

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