Thin and Thick Samples

The simple linear relation between observed count rate R of analyte element i and its concentration q shown in Eq. (9) is only valid in a limited number of cases. In general, for monochromatic forms of excitation (with energy Eq) 3tid in the absence of enhancement phenomena, the observed XRF count rate R of an element i (with fluorescent energy E ) is related to the sample thickness d and its concentration Cj in the following manner (see also Eq. (34)—(36))  

In many practical situations, it is important to ensure that the sample presented for analysis is sufficiently thick (i. e. thicker than the highest critical penetration depth among the various fluorescent signals being used), so that the observed analytical signals no longer depend on sample thickness but only on analyte concentration. 

Next to the critical penetration depth it is also useful to define a critical thickness below which absorption and enhancement effects can be neglected. For analysis of such thin-fihn samples, the calibration relations of Eq. (8) and (9) are valid and matrix effect corrections need not be applied. By convention, dthi corresponds to the situation where the total attenuation in the sample is equal to 1 %. Table 11.7 lists typical dthm values for various fluorescent line energies in two matrices. 

Energy/Wavelength of K line Element E/keV A/nm Excitation Spectrum Tube anode Critical Penetration Depth dMdJpm Silicate Steel Thin Film Thickness d n/pm Silicate Steel  

Primary and Secondary Absorption, Direct and Third Eiement Enhancement 

---

Cohen, D.D., Siegele, R., Orlic, I. Stelcer, E. (2001) Long term accuracy and precision of PIXE and PIGE measurements for thin and thick sample analysis. Proceedings of the 9th International PIXE Conference, Guelph, 8-12 June. 

Based on the analysis made for thousands of thick obsidian and pottery samples analyzed over a six-year period, the accuracy and precision of PIXE measurements for thin and thick sample analyses have been foimd to be as low as 1.6% for major elements with precision ranging from 5% to 10% depending on the elemental concentration (Cohen 2002). 

Example 3.3.1 The reduction of flat particles of high-density nickel oxide in hydrogen for two different sizes of thin and thick samples gave the following results under the identical conditions but in the absence of resistance due to external mass transfer ... 

Predictions we will only see the abundance trend in the one satellite that finally settles in a torus at our R the abundance trends will differ depending on the potential well of the satellite, it must be largish and not a dSph no age gap between thin and thick disk as thin disk is accreted also at early times Observations tight trends in kinematically selected samples so far all studied thick disk stars are older than thin disk stars... 

In order to investigate the chemical and age properties of the thin and the thick disks separately we have performed the deconvolution of their velocity distributions. We show that about 25% of the sample has kinematics typical of the thick disk, adopting for its parameters V ag = — 51km s 1 and (<7u, v, w) = (63, 39, 39) km s-1. Stars having a probability higher than 80% to belong to the thin and thick disks were selected. Plots on Fig.l show nicely the... 

Figure 5. Magnetization loops of FeCoV (20nm) / NiO(tN j() nm) / FeCoV(20 nm) samples at 2 K, after field cooling from room temperature under various cooling fields depicted in the figure after saturating the sample at 5 kOe. The individual M-H loops from each FeCoV layers are shifted in opposite directions (as shown by thin and thick arrows), indicating that the exchange coupling has opposite nature at the two interfaces.

Figure 4.1 Beta particle emission from thin and thick radioactive samples.

Figure 10.10 shows the temperature variation of the (100) peak intensity measured by GOD for three samples of different thickness. It shows a continuous decrease in intensity versus temperature for samples of thickness above 200 nm and 48 nm but a nearly constant intensity for the thinnest sample of thickness 11 nm up to about 70 °C followed by a sharp drop. The same behaviour was also found for a 17 nm thick sample but in a different experiment performed at DELTA (not shown here). This much thinner sample t= Q nm) exhibits a sharp drop of (100) intensity at 80 °C. This behaviour can be interpreted by a strong substrate-layer interaction becoming remarkable for thin films only. The interaction also modifies the character of phase transition. It appears as a continuous drop of intensity for thick films but a sharp drop of intensity was found for thin films. Similarly, the inter-planar distances elevated temperatures indicate that all the curves of the thin and thick films show an increase of t(ioo up to the temperature of the intensity drop. The inter planar distances ( t( ) values are reversible as long as it is not heated beyond the melting point, while the intensity was always found to decrease after cool-... 

When variations occur in the quality of a raw material, it may be difficult to procure samples of thin and thick liquor that correspond to the same batch of raw material. If so, the thin liquor for testing should be prepared by diluting a portion of the thick liquor. Studies... 

The amount of radiation absorbed with an UVA is related to its concentration and extinction coefficient as well as to the sample thickness according to the Lambert Beer law. The internal layers far from the surface of the article are more protected than superficial ones. This is the main limitation of UVA that makes them suitable mainly for thick articles. Nevertheless the performance of UVA may be improved both in thin and thick articles when used in combination with HALS. 

Compared to EDS, which uses 10-100 keV electrons, PEXE provides orders-of-magnitude improvement in the detection limits for trace elements. This is a consequence of the much reduced background associated with the deceleration of ions (called bremsstrahlun compared to that generated by the stopping of the electrons, and of the similarity of the cross sections for ioiuzing atoms by ions and electrons. Detailed comparison of PIXE with XRF showed that PDCE should be preferred for the analysis of thin samples, surfrce layers, and samples with limited amounts of materials. XRF is better (or bulk analysis and thick specimens because the somewhat shallow penetration of the ions (e.g., tens of pm for protons) limits the analytical volume in PIXE. 

Table 5 compares the tensile properties of Vectra A950 in the form of dispersed fibers and droplets in the matrix by injection molding, microfibril by extrusion and drawing [28], injection molded pure thick sample and pure thin sample, and the pure drawn strand [28]. As exhibited, our calculated fiber modulus with its average of 24 GPa is much higher than that of the thick and thin pure TLCP samples injection molded. It can be explained that in cases of pure TLCP samples the material may only be fibrillated in a very thin skin layer owing to the excellent flow behavior in comparison with that in the blends. However, this modulus value is lower than that of the extruded and drawn pure strand. This can be... 

---