Secondary Target Arrangement Research Articles

The advantages of using digital signal processing in polarized x-ray fluorescence analysis

Improving the specificity and productivity of XRF is of great relevance for the determination of trace elements in samples of diverse origin. The advantages of using digital signal processing in energy-dispersive polarized x-ray fluorescence analysis are demonstrated by comparing the instrumental sensitivities achieved with those obtained by using a conventional analogue signal processing-based spectrometer. A compact geometry secondary target arrangement was designed to increase the effective solid angles and to reduce the distances between secondary target, sample and detector, thus achieving larger x-ray fluxes for both the excitation and detection process, resulting in improved instrumental sensitivities. The performance of both spectrometers was evaluated for two different detectors: an Si(Li) detector and a thermoelectrically cooled passivated-implanted planar silicon detector (X-PIPS). The uncertainties achieved and accuracy are illustrated for the analysis of a group of sediment and organic-origin certified reference materials using two different quantitative procedures. Copyright © 2006 John Wiley & Sons, Ltd.

L X-ray fluorescence cross-sections of heavy elements excited by 16.04, 16.90 and 17.78 keV photons

Abstract L l , L α , L β , L γ X-ray fluorescence cross sections have been measured for the elements Au, Pt, W, Lu, Yb, Tm, Ho, Dy and Tb using photon energies of 16.04, 16.90 and 17.78 keV. Measurements have been performed using an X-ray tube with a secondary-exciter system as an excitation source. The secondary exciters used are Zr, Nb and Mo of pure metal sheets (99.99%). A Mo X-ray tube with a secondary-target arrangement was used to obtain high intensity with a high degree of monochromaticity. Using an X-ray tube made it possible to measure X-ray fluorescence cross-sections and intensity ratios even for low intensity X-ray lines. The experimental values of the cross-sections were determined by measuring the absolute yield of L subshell X-rays emitted from a standard target of a given element irradiated with photons of given energy. The theoretical values of the cross-sections were calculated using theoretically tabulated values of subshell photoionization cross-sections, fluorescence yields, Coster–Kronig transition probabilities and radiative decay rates. Experimental results have been compared with the theoretically calculated values of L X-ray cross-sections. A fairly good agreement is observed between the experimental and the calculated values. The intensity ratios I Lβ / I Lα and I Lγ / I Lα were measured and found to be in good agreement with the calculated values.

A new method to estimate elastic scattering cross sections in the X-ray region and the associated anomalous dispersion

Using nearly monoenergetic unpolarised Kα radiation, we have measured the elastic scattering cross sections for Pt, Au and Pb in the energy region 5.41 ≤ E ≤ 9.23 keV. The experimental results for Pt, Au and Pb are new. A new X-ray scattering system was assembled using an X-ray tube and secondary targets. In order to improve the peak-to-background ratio and the efficiency of the detection system, particularly in the low-energy region, excitation source, sample and detector assembly were placed in a vacuum chamber at a pressure of 10 −2 mbar. The present system helped considerably in reducing the scattering and background effects, and in removing the interference of Ar K X-rays which fall in the investigated regions. A new method was developed to estimate the degree of monochromaticity, geometrical effects of the measuring system, solid angle correction and some considerations which are necessary in experiments using X-ray tube with secondary target arrangement. Experimental elastic scattering cross sections are compared with theoretical estimates, a combination of relativistic modified form factors with angle independent anomalous scattering factors (RMF + ASFs) and recent theoretical estimates based on the multipole expansion of the second order S-matrix approach. Deviations are observed around the edges (high energy side) indicating the importance of the dispersion correction terms. The present experimental results are useful taking into account that the available calculated values describe the free atom and deviations for a solid have to be expected. This is due to the difference of the electronic structure of the solid in comparison to the free atom as a base for theoretical estimations. However, the comparison of experimental results with theoretical estimates indicates the importance of numerical calculations based on the multipole expansion of the second order S-matrix approach and high energy limit values (RMF + ASFs).

Elastic scattering and the associated anomalous dispersion in the vicinity of Cd, In, Sn and Sb, K-absorption edges

Using nearly monoenergetic unpolarized Kα X-rays with energies E = 17.44-42.75 keV, differential elastic scattering cross sections for Cd, In, Sn and Sb were measured at an angle of 90° to assess the contribution of anomalous dispersion in the vicinity of K-absorption edges. An X-ray tube with a secondary target arrangement was used to obtain the monoenergetic radiation. A new method is developed to estimate the degree of monochromaticity, geometrical effects of the measuring system, solid angle correction and some considerations which are necessary in experiments using an X-ray tube with secondary target arrangement. Experimental results are compared with theoretical elastic scattering cross sections calculated using relativistic form factors (RFFs), relativistic modified form factors (RMFs), a combination of RFFs, RMFs and angle-independent “anomalous” scattering factors (ASFs), and relativistic numerical calculations based on multipole expansion of the second order S-matrix approach. Fairly good correspondence is observed between the experimental results and a combination of RFFs with ASFs above and below the edges. The experimental results are in excellent agreement with S-matrix values and a combination of RMFs with ASFs above and below the edges of Cd, In, Sn and Sb. However, the differences are larger nearer to the edges indicating the importance of anomalous terms in reproducing “anomalous” behaviour of the K-threshold regions.

Estimation of monochromaticity, solid angle correction and some considerations on secondary target arrangement using x-ray tube

A new method is developed to estimate the degree of monochromaticity, geometrical effects of the measuring system, solid angle correction and some considerations on bremsstrahlung induced fluorescence radiation. The need of these parameters and their use in secondary target arrangements are thoroughly discussed.

Measurement of L x-ray fluorescence cross-sections in heavy elements excited by 17.78, 25.88, 26.88 and 32.89 keV photons

L 1, L α, L β and L γ x-ray cross-sections have been measured for the elements Au and Pb at excitation energies 17.78, 25.78, 26.88 and 32.89 keV. Measurements have been performed using an x-ray tube with a secondary exciter system as the excitation source. The x-ray tube with a secondary target arrangement was used to obtain high intensity with high degree of monochromatization. By using an x-ray tube it is possible to measure L x-ray fluorescence cross-sections even for low intensity x-rays (L 1). Experimental results have been compared with theoretical values. A fairly good correspondence is observed between experimental and calculated values.

Photon‐excited K x‐ray fluorescence cross‐sections for some light elements in the energy range 20–60 keV

AbstractKα and Kβ x‐ray fluorescence cross‐sections were experimentally determined for elements in the range 26 ⩽ Z ⩽ 40 at various excitation energies using and x‐ray tube with a secondary exciter system as the excitation source. The x‐ray tube with a secondary target arrangement was used to obtain high intensity with a high degree of monochromatization. Experimental values were compared with the theoretical values calculated using IKβ/IKα ratios based on Hartree—Fock and Hartree—Slater theories. The experimental values for all the elements at various excitation energies were in good agreement with the theoretical values.

Measurements of L1, Lα, Lβ and Lγ x‐ray fluorescence cross‐sections in heavy elements excited by 36.62, 43.69, 48.30, 50.20 and 53.50 keV photons

AbstractL1, Lα, Lβ and Lγ x‐ray fluorescence cross‐sections were measured in Au and Pb at excitation energies of 36.62, 43.69, 48.30, 50.20 and 53.50 keV. Measurements were made using an x‐ray tube with a secondary exciter system as the excitation source. The x‐ray tube with a secondary target arrangement was used to obtain high intensity with a high degree of monochromatization. By using an x‐ray tube it is possible to measure L x‐ray fluorescence cross‐sections even for low‐intensity x‐rays (L1). The experimental results were compared with the theoretically calculated values of L x‐ray fluorescence cross‐sections and a fairly good correspondence was observed.

L X-ray fluorescence cross sections of heavy elements excited by 15.20, 16.02, 23.62 and 24.68 keV photons

L X-ray fluorescence cross sections have been measured for the elements La, Ce, Gd, Er and Au using photon energies of 15.20, 16.02, 23.62 and 24.68 keV. Measurements have been performed using an X-ray tube with a secondary exciter system as the excitation source. The X-ray tube with a secondary target arrangement was used to obtain high intensity with a high degree of monochromatization. By using an X-ray tube it is possible to measure X-ray fluorescence cross sections even for low-intensity X-rays (L 1). Experimental results have been compared with the theoretically calculated values of L X-ray fluorescence cross sections. A fairly good correspondence is observed between experimental and calculated values.

L-shell x-ray intensity ratios for Au and Pb at excitation energies 36.82, 43.95, 48.60, 50.20 and 53.50 keV

The L-shell x-ray intensity ratios I(L1)/I(Lα), I(Lβ)/I(Lα) and I(Lγ)/I(Lα) for Au and Pb have been measured at the excitation energies 36.82, 43.95, 48.60, 50.20 and 53.50 keV with a HP Ge(Li) detector. Measurements have been performed using an x-ray tube with a secondary exciter system as the excitation source. The x-ray tube with a secondary target arrangement was used to obtain high intensity with high degree of monochromatisation. A comparison is made of the experimental results with the calculated values obtained by using theoretical x-ray emission rates, sub shell ionisation cross-sections sub shell fluorescence yields and Coster-Kronig transition probabilities. A fairly good agreement is observed between experimental and theoretical values. The intensity ratios for intense transitions ILβ/ILα are in good agreement with the theoretical values.

K X-ray fluorescence cross-sections for some light elements excited by keV photons

Kα and Kβ X-ray fluorescence cross-sections have been experimentally determined for the elements Cu, Se, Y, and Mo at excitation energies 23.62, 24.68, 36.82, 43.95, 48.60, and 50.20keV using an X-ray tube with a secondary exciter system as the excitation source. The X-ray tube with a secondary target arrangement was used to obtain high intensity with high degree of monochromatization. Experimental values were compared with the theoretical values using tabulated I\({{I_{K_\beta } } \mathord{\left/ {\vphantom {{I_{K_\beta } } {I_{K_\alpha } }}} \right. \kern-\nulldelimiterspace} {I_{K_\alpha } }}\) ratios based on Hartree-Fock and Hartree-Slater theories calculated by Scofield. The experimental values for all the elements at various excitation energies are in good agreement with the theoretical values.

L x-ray fluorescence cross sections and intensity ratios in some high-Z elements excited by 23.62- and 24.68-keV photons.

Ll, L\ensuremath{\alpha}, L\ensuremath{\beta}, and L\ensuremath{\gamma} x-ray fluorescence cross sections have been measured for the elements Pr, Ho, Yb, Au, and Pb using photon energies of 23.62 and 24.68 keV. Measurements have been performed using an x-ray tube with a secondary-exciter system as the excitation source. The secondary exciters of Cd and In were pure metals (g99.9%). The x-ray tube with a secondary-target arrangement was used to obtain high intensity with a high degree of monochromatization. By using an x-ray tube, it is possible to measure x-ray fluorescence cross sections and ratios even for low-intensity x rays (Ll). Experimental results have been compared with the theoretically calculated values of L x-ray fluoresence cross sections. A fairly good correspondence is observed between experimental and calculated values. The intensity ratios for the intense transitions ${\mathit{I}}_{\mathit{L}\mathrm{\ensuremath{\beta}}}$/${\mathit{I}}_{\mathit{L}\mathrm{\ensuremath{\alpha}}}$ are in good agreement with the calculated values.