Other Ion Counting Techniques

Fission track analysis (FTA) is an indirect method of counting heavy ions that are created through nuclear fission of fissile nuclides when a sample is bombarded by neutrons. The sample is placed between two thin layers of polymeric film and placed near a neutron source. The interaction of the neutrons with fissile nuclides, like or 239pu, 

Electroanaly deal (EA) methods can also be considered as ion counting techniques that are used to selectively measure the potential generated between two electrodes or the currents produced by certain types of ions that are present in a liquid sample. The selectivity is achieved by deploying a specially tailored coating on an electrode that allows only a specific ion type to register a current. In other embodiments, elec-troanalytical methods can be used to preconcentrate a specific ion and then it can be detected and quantified by stripping the charge from the same electrode or by 

FIGURE 1.30 A schematic representation of the laser ablation—ICPMS system. (From Gunther, D. and Hattendorf, B., TrAC, 255, 2005. With permission.) 

Other analytical techniques. Electroanalytical methods can also be used to differentiate between ionic species (based on valence state) of the same element by selective reduction or oxidization. In brief, the electroanalytical methods measure the effect of the presence of analyte ions on the potential or current in a cell containing electrodes. The three main types are potentiometry, where the voltage difference between two electrodes is determined, coulometry, which measures the current in the cell over time, and voltammetry, which shows the changes in the cell current when the electric potential is varied (current-voltage diagrams). In a recent review article, 43 different EA methods for measuring uranium were mentioned and that literature survey found 28 voltammetric, 25 potentiometric, 5 capillary electrophoresis, and 3 polarographic methods (Shrivastava et al. 2013). Some specific methods will be discussed in detail in the relevant chapters of this tome. 

This was also mentioned earlier in context with mass spectrometry and LIBS. The unique system is suitable for direct analysis of solid samples and combines the sensitivity and isotopic measurement capability of the ICPMS with the spatial resolution of a laser system shown in Fignre 1.30 (Gnnther and Hattendorf 2005). The system combines a pulsed laser, preferably with short wavelength photon (like 193 nm from an excimer laser) in order to achieve clean ablation without melting of the sample with an ICPMS instrument (any kind is suitable). The sample is placed in a chamber (ablation cell) and a flow of gas (nsnaUy argon with some helium) carries the particles that are ablated from the sample by the laser into the torch of the ICPMS. 

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