Analysis of light elements

In the analysis of light elements where the wavelength differences to be resolved are large and it is difficult to get good crystals, pulse-height, selection has a promising future. 

PIGE is a rapid, non-destructive technique that is employed in the analysis of light elements such as lithium (10-100 ppm limit of detection), boron (500-1000 ppm limit of detection), and fluorine (1-10 ppm limit of detection), which are often difficult to determine by other analytical means. Because the technique is based upon specific nuclear reactions, the sensitivity of PIGE varies greatly from isotope to isotope, and this non-uniformity of sensitivity has limited its widespread use as a complementary technique to micro-PIXE. 

Barrie, A., Prosser, S.J. Automated analysis of light-element stable isotopes by isotope ratio mass spectrometry. Unpublished Materials. Europa Scientific Ltd. Crewe, Cheshire, England, 2000. 

Figure 1. K-shell fluorescence yields as a function of the atomic number. Light element region is magnified. It can be seen that only a few photons are emitted out of one thousand ionizations in case of the lightest elements. As a consequence, analysis of light elements with EDX is less efficient than with EELS or AES.

Surface of the cooled detector would attract contamination from the residual gases of the vacuum. To prevent the detector from being contaminated, the vacuum space of the detector is separated from that of the microscope by a thin window. The window itself is thermally isolated from the cold detector, so it does not attract contamination. An unwanted byproduct of the presence of this window is the absorption of the photons (to be detected) by the window. Softer radiation (of lighter elements) is affected more. This is the second problem with the analysis of light elements with EDS. 

To verify this hypothesis, low volume samplers have been operated in parallel with the air pollution control district s Km samplers. The samples collected were analyzed optically for elemental carbon and by the Gamma Ray Analysis of Light Elements (GRALE) technique for total carbon. These data were used to assess the concentration of elemental and total carbon aerosols present during the winter months in Los Angeles. It was established that the Km samplers can be calibrated to read elemental carbon concentrations. This calibration can be used to reconstruct historical elemental carbon levels at seven sites in Los Angeles. 

Aerosol carbon concentrations have been measured at two sites in the Los Angeles basin. Samples were analyzed for total carbon content and for elemental carbon content by the Gamma Ray Analysis of Light Elements technique and by several optical methods. Elemental carbon was shown to constitute a substantial fraction of total carbonaceous aerosol mass in the wintertime in Los Angeles. 

S. Gas source mass spectrometry (GSMS) with electron impact (El) ion source produces nearly mono-energetic ions (similar to TIMS) and is an excellent tool for the high precision isotope analysis of light elements such as H, C, N and O, but also for S or Si.7,100,101 Precise and accurate measurements of isotope ratios have been carried out by gas source mass spectrometers with multiple ion collectors by a sample/standard comparison and the 8 values of isotope ratios were determined (see Equation 8.4). Electron impact ionization combined with mass spectrometry has been applied for elements which readily form gaseous compounds (e.g., C02 or S02) for the isotope analysis of carbon and sulfur, respectively). 

SIMS and SNMS are versatile analytical techniques for the compositional characterization of solid surfaces and interfaces in materials research.92-94 As one of the most important applications, both surface analytical techniques allow depth profile analysis (concentration profile as a function of the depth analyzed) to be performed in materials science and the semiconductor industry with excellent depth resolution in the low nm range. For depth profiling in materials science, dynamic SIMS and SNMS using high primary ion beam doses are applied. Both techniques permit the analysis of light elements such as H, , C and N, which are difficult to measure with other analytical techniques. 

R.B. Bouiton, G.T. Ewan, Simultaneous analysis of light elements using prompt nuclear reaction gamma rays, Anal. Chem. 49 (1977) 1297-1303. 

G. Demortier, Analysis of light elements with a nuclear microprobe - a review, Nucl. Instr. Meth. B104 (1995) 244-254. 

Quantitative analysis of light elements (4these elements (low radiation energy, low emission yield) and a certain number of complications make it impracticable in the majority of situations ... 

Streli C, Wobrauschek P, Bauer V, Kregsamer P, Goegl R, Pianetta P, Ryon R, Pahlke S, Fabry L (1997) Total reflection X-ray fluorescence analysis of light elements with synchrotron radiation and special X-ray tubes. Spectrochim Acta 52 861-872... 

Streli C (1997) Total reflection X-ray fluorescence analysis of light elements. Spectrochim Acta 52 281-293... 

Electronically controlled goniometers with separate theta and 2-theta stepper motors ensure high precision and automatic adjustment of the instrument. Collimator changers with up to four positions can be equipped with suitable collimators to provide the best measuring conditions for any applications from increased sensitivity for light elements to improved resolution for rare earth elements (Fig. 5). Sophisticated crystals for the user s application, e.g. artificial multilayer crystals for analysis of light elements, are also available. 

The main power of the method is the analysis of light elements (i.e., Ca and below). Their capture cross sections are characteristically a few tenths of a barn, which allows their assay even in weak neutron beams (e.g., the industrial analysis of raw materials using neutron generators). The most important of them is hydrogen, which can be analyzed with a fairly good sensitivity in almost any kind of matrix. PGAA is a unique tool for the determination of hydrogen or water content even in trace amounts. 

Ali MY, El-Megrab AM, Jonah SA, Su D, Varadi M, Csikai J (1995) Nucl Geophys 9 203 Aoki T, Baba M, Ibaraki M, Miura T (2000) Feasibility study on non-destructive analysis of light elements by fast neutron back-scattering technique, radiation detectors and their uses. In Sasaki S, Shibata T, Takahashi H, Nakazawa M (eds) KEK proceedings 2000-14, KEK, Japan, p 163... 

These advantages make the ion-y reactions a particularly useful elemental analysis technique. Because the detection technique is different from the detection of both X-rays in PIXE and particles in RBS and NRA, the method got in practice a distinctive name particle-induced 7-ray emission (PIGE), where the word particle means mostly proton. PIGE is often used simultaneously with PIXE, and its suitability for the analysis of light elements (mainly Li, B, F, Na, Mg, Al, and Si) complements the performance of PIXE well. Among y-ray emissions induced by various types of particles, the deuteron-induced 7-ray emission (DIGE) deserves the most practical interest, because it is also sensitive to C, N, and O, and its high cross sections... 

Recently, a code was developed for the quantitative PIGE analysis of light elements without standards in thick samples (Mateus et al. 2005). (The code works similarly to what is done for PIXE via integrating cross sections deduced from precisely measured nuclear reaction excitation functions along the depth of the sample.)... 

In the analysis of light elements by PIGE, the reactions by Coulomb excitation (p, p y) are common. The resonance nuclear reactions (p, y), (p, ay) are used occasionally for the depth-profile. 

Mateus et al. (2005) have recently developed a code for the quantitative analysis of light elements in thick samples by PIGE. The method avoids the use of standards in the analysis, using a formalism similar to the one used for PIXE analysis, where the excitation function of the nuclear reaction related to the y-ray emission is integrated along the depth of the sample. To check the validity of the code, these authors have presented results for the analysis of lithium, boron, fluorine and sodium in thick samples. The experimental values of the excitation functions of the reactions Li(p, p yj Li, °B(p, ay ) Be,... 

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