Sorting with lasers

The Applications of Laser-induced Time-resolved Spectroscopic Techniques chapter starts with a short description of laser-induced spectroscopies, which may be used in combination with laser-induced luminescence, namely Breakdown, Raman and Second Harmonic Generation. The chapter contains several examples of the application of laser-based spectroscopies in remote sensing and radiometric sorting of minerals. The proljlem of minerals as geomaterials for radioactive waste storage is also considered. 

Figure 9.19 Scale analysis of North Sea houting from Ijsselmeer lA-ICP-MS, a) photograph of a scale, b) part of a scale with laser craters obtained by LA-ICP-MS measurement in line scan modus, c) Sr Ca ratio for nine North Sea houting caught in Ijsselmeer in 2001/2002. The results were sorted into three different types A Fish that only lived in freshwater B Fish that lived for a fairly long period in fresh water, then moved to sea water and returned to fresh water where they were caught C Fish that obviously moved quickly to sea water after hatching (period from hatching in fresh water until the arrival in the sea was to short to measure a ratio that normally indicates fresh water) and returned to...

The first theoretical attempts in the field of time-resolved X-ray diffraction were entirely empirical. More precise theoretical work appeared only in the late 1990s and is due to Wilson et al. [13-16]. However, this theoretical work still remained preliminary. A really satisfactory approach must be statistical. In fact, macroscopic transport coefficients like diffusion constant or chemical rate constant break down at ultrashort time scales. Even the notion of a molecule becomes ambiguous at which interatomic distance can the atoms A and B of a molecule A-B be considered to be free Another element of consideration is that the electric field of the laser pump is strong, and that its interaction with matter is nonlinear. What is needed is thus a statistical theory reminiscent of those from time-resolved optical spectroscopy. A theory of this sort was elaborated by Bratos and co-workers and was published over the last few years [17-19]. 

For separation between microcline and plagioclase X-ray excited luminescence is used (Gorobets et al. 1997). The main problem is that their emission spectra are very close. Under laser excitation these minerals also demonstrate blue emissions connected with Eu ", which have close spectral and kinetic parameters. Nevertheless, the differences in excitation spectra (Fig. 8.5) enable effective sorting. 

For the second task second harmonic generation by quartz has been proposed. The first procedure is to determine the relative intensity of SH compared with etalon, where the ratio of SH intensities is used for sorting. In the second procedure the laser source is working with a very high repetition rate and the number of pulses with SH intensity above a certain level is used as the separation criterion. Sorting using non-linear optics may be very effective, because... 

The possibilities of time-resolved laser based spectroscopies have been demonstrated, combining such techniques as luminescence, Raman, breakdown and second-harmonic generation. Radiometric sorting of minerals using LIBS was patented and apparatus for evaluation of phosphate rocks with elevated dolomite content has been developed and constructed. 

The modes of thinking about structures and reactions and intermediates facilitated or even demanded by these conceptual innovations meshed productively with new tools of a different sort to drive the progress of recent decades. Advances in electronics and computers, all sorts of spectroscopy, laser optics and physics, chromatography, mass spectrometry, quantum theory and computational strategies, molecular beam experiments, and so on, radically expanded the limits of experimental and theoretical investigations. 

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