1,720,993 research outputs found
L-X-RAY FLUORESCENCE CROSS-SECTIONS IN THE ATOMIC REGION 46-LESS-THAN-Z-LESS-THAN-51 EXCITED BY 6.47, 7.57 AND 8.12 KEV PHOTONS
No full textTotal L X-ray fluorescence cross sections have been measured for the elements Sb, Sn, In, Cd, Ag and Pd excited by 6.47, 7.57 and 8.12 keV photons. The measurements have been performed using an X-ray tube with a modified secondary exciter system as the excitation source. In order to improve the efficiency of the detection system, the excitation source, detector and the target assembly were placed in a vacuum chamber. The measurements were made at a pressure of 10(-2) mbar. The present system considerably reduces the scattering and background effects and improves the monochromaticity. The experimental results have been compared with the theoretical values evaluated using L-subshell fluorescence yields (omega(i)) and Coster-Kronig transition probabilities (f(ij)) based on relativistic Dirac-Hartree-Slater (RDHS) theory. It is observed that the L X-ray cross-section values for the elements in the region are in good agreement with the theoretical values based on RDHS theory. The average L-shell fluorescence yields have also been computed using the experimentally measured cross-section values and the theoretical photoionization cross sections. The average fluorescence yields have been compared with the available results in the literature
L X-RAY-FLUORESCENCE CROSS-SECTIONS AND INTENSITY RATIOS IN SOME HIGH-Z ELEMENTS EXCITED BY 23.62-KEV AND 24.68-KEV PHOTONS
No full textLl, Lalpha, Lbeta, and Lgamma 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 (> 99.9%). 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 I(Lbeta)/I(Lalpha) are in good agreement with the calculated values
COHERENT AND INCOHERENT-SCATTERING OF 42.75 AND 47.24 KEV X-RAY PHOTONS SCATTERED FROM AL, CU, Y, MO, AU AND PB
No full textUsing nearly monoenergetic unpolarized K alpha x-ray photons, measurements were made of the coherent and Compton scattered intensity in the atomic region 13 less than or equal to Z less than or equal to 82 at an angle of 90 degrees with a high-resolution Si(Li) detection system. In order to improve the efficiency of the detection system, the excitation source, detector and the sample assembly were placed in a vacuum chamber and a pressure of 10(-2) mbar was maintained throughout the measurements. Experimental scattering cross-sections are compared with the normalized integrated cross-sections based on form factor and incoherent scattering functions, Experimental coherent scattering cross-sections are higher than the theoretical values, indicating the resonance behaviour, fine structure effects and oscillation of coherent intensity around the absorption edges. Experimental incoherent scattering cross-sections are lower than the theoretical estimates for heavy elements, indicating the effect of electron binding at low photon energies
L X-RAY-FLUORESCENCE CROSS-SECTIONS OF HEAVY-ELEMENTS EXCITED BY 15.20, 16.02, 23.62 AND 24.68 KEV PHOTONS
No full textL 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 (L1). 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
Metal location and thickness in a multilayered sheet by measuring K alpha/K beta, L alpha/L beta and L alpha/L gamma X-ray ratios
No full textWhen a multilayered material is analyzed by means of energy-dispersive X-ray fluorescence analysis, then the X-ray ratios of K alpha/K beta, or L alpha/L beta and L alpha/L gamma, for an element in the multilayered material, depend on the composition and thickness of the layer in which the element is situated, and on the composition and thickness of the superimposed layer (or layers). Multilayered samples are common in archaeometry, for example, in the case of pigment layers in paintings, or in the case of gilded or silvered alloys. The latter situation is examined in detail in the present paper, with a specific reference to pre-Columbian alloys from various museums in the north of Peru. (C) 2009 Elsevier B.V. All rights reserved
Compton energy-absorption scattering cross-sections for H, C, N, O, P, Ca and assessment of Doppler broadening
No full textTotal Compton, individual shell and Compton energy-absorption scattering cross-sections are evaluated in the energy region 0.005 to 10 MeV for H, C, N, O, P and Ca. Compton energy absorption cross-sections deviate numerically with available values. The cause of the numerical discrepancies are not fully understood but can be attributed to Doppler broadening of the Compton scattered photons through a given angle
Geometrical factor influence on Compton profile measurement for biological samples
No full textThe Compton profile is a correction of the Klein-Nishina cross-section for the motion of the electrons. This correction modifies the shape of the Compton peak in the spectrum of the scattered photons and it depends on the atomic wave functions of the electrons inside the sample. Thus, the Compton profile can be used as a probe for the electronic structure of atoms or molecules. However, the shape of the Compton peak is also influenced from the geometrical factors or apertures of collimators used in the experimental setup. Since the energy of the Compton scattered photons depends on the scattering angle, in principle, the best choice is to collimate the detector as much as possible, but, as a drawback, this means also a drastic reduction of the photon flux at the detector. This paper deals with a study of the influence of the geometrical factor on the discrimination of different biological elements. The results can be extended to other materials. Some results from reference biological samples are reported and discussed
PHOTON-EXCITED K X-RAY-FLUORESCENCE CROSS-SECTIONS FOR SOME LIGHT-ELEMENTS IN THE ENERGY-RANGE 20-60 KEV
No full textKalpha and Kbeta x-ray fluorescence cross-sections were experimentally determined for elements in the range 26 less-than-or-equal-to Z less-than-or-equal-to 40 at various excitation energies 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. Experimental values were compared with the theoretical values calculated using I(Kbeta)/I(Kalpha) 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
Synchrotron-based small-angle x-ray scattering from biogenic materials
No full textWe examine the small-angle x-ray scattering (SAXS) from samples of biogenic nature to study soft-matter and the associated biology. Biogenic samples are prepared from soft tissues. SAXS from different tissues varies according to both genetic (species) and environmental (habitant differences) factors. SAXS spectra (intensity versus energy (MeV)) at different Q momentum transfer values provide the crucial tool for determining the structure and enhancement of the desired property, e. g. biological activity. Fourier transform infrared (FTIR) spectroscopy was used to characterize the presence of specific chemical groups in the materials. These methods are valuable to identify various phases of calcium carbonate (CaCO(3)). FTIR spectra were obtained in the range of wavenumbers from 4000 to 400 cm(-1) for the external shell, soft tissue and operculum at room temperature. Finding information about the biological structures from these low-absorbing materials is one of the most important goals in the field of biological and environmental sciences and to know the mechanisms involved in bio-mineralization. These results will be utilized for the development of bio-systems
Embedded soft-tissue image mechanism of a small animal shell with synchrotron-based micro-CT
No full textSynchrotron-based micro-CT was utilized to image the embedded biological soft-tissue of a small animal shell. Micro-CT images of the biological soft-tissue were acquired using 20, 25, and 27 keV synchrotron X-rays with contrast agents, such as water, physiological saline and iodine. Visualized the complex features of the animal at the above energies with water, physiological saline and iodine. The choice of the optimum energy was chosen based on the contrast mechanisms to know more about soft-matter and the associated internal complex biological features of the small animal shell. This way, the images at 27 keV (optimum energy) was reasonably acceptable for better visualization of the interior micro-architecture, such as soft-anatomy, physiology and internal organs of the animal with better visibility. The introduction of water, physiological, or iodine as contrast agents is shown to enhance minute image features in synchrotron-based tomographic imaging
- …
