D.V. Rao

Coherent and incoherent scattering of 14.93, 17.44 and 21.12 keV photons from Al, Cu, Sr, Cd, Ce, Pr, Sm, Pt, Au and Pb

Coherent and incoherent scattering cross sections for the elements Al, Cu, Sr, Cd, Pr, Ce, Sm, Pt, Au and Pb have been measured at 14.93, 17.44 and 21.12 keV Kα x-ray energies. Measurements have been performed using an x-ray tube with a secondary exciter system as the excitation source instead of radioisotopes. Bremsstrahlung radiation from the x-ray tube has been used to excite nearly monoenergetic x-rays in secondary targets. In order to improve the efficiency of the detection system the excitation source detector and the target assembly were placed in a vacuum chamber and a pressure of 10−2 mbar is maintained throughout the measurements. The coherently and incoherently scattered intensity by the sample into the detector has been detected at an angle of 90° using low energy HP Ge and Si (Li) photon detectors. The present system considerably reduced the scattering and background effects and improved the monochromacy. Experimental scattering cross sections are compared with the normalised integrated cross section based on form factor and incoherent scattering approximations. The present experimental results do not strongly support any set of theoretical values. More accurate experimental results and extended exact calculations of atomic form factors at more closely spaced values of incident x-ray energies and scattering angles are clearly needed if more meaningful comparison between experiment and theory are to be possible.

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

Abstract 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.

Total M X-ray fluorescence cross sections and fluorescence yields for Pt, Au and Pb in the energy region 5.47 ≤ E ≤ 9.36 keV

Abstract Total M X-ray fluorescence cross sections for the elements Pt, Au and Pb have been measured at incident photon energies 5.47, 5.96, 7.04, 8.14, 8.74 and 9.36 keV. Average M-shell fluorescence yield at each incident photon energy has been deduced, using the experimental total M X-ray fluorescence cross section and theoretical M-shell photoionisation cross sections. Experimental total M X-ray fluorescence cross sections and M-shell fluorescence yields are found to be in good agreement with the theoretical estimates based on relativistic Dirac-Hartree-Slater theory.

L X-ray fluorescence cross sections in the atomic region 46⩽Z⩽51 excited by 6.47, 7.57 and 8.12 keV photons

Abstract Total 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 (ωi) and Coster-Kronig transition probabilities ( ƒ 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.

M X-ray fluorescence cross sections and yields in the atomic region 78 ⪕ Z ⪕ 82 excited by 6.47 and 7.57 keV photons

Abstract Experimental M X-ray fluorescence cross sections for the elements Pt, Au and Pb have been measured at incident photon energies 6.47 and 7.57 keV. Theoretical M X-ray fluorescence cross sections for the elements Yb, W, Hg, Tl, Bi and Ra at 6.47 and 7.57 keV are also calculated. Experimental results are compared with the theoretical values based on relativistic Dirac-Hartree-Slater calculations of Chen et al. and non-relativistic calculations of McGuire. The average M shell fluorescence yields ω M have been deduced using experimental cross section values and the theoretical M shell photoionization cross sections. Results are compared with the available theoretical 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.

Ll, Lα, Lβ and Lγ X‐Ray Fluorescence Cross‐sections for Ce, Pr and Sm Excited by Y and Mo Kα X‐Ray Photons

Ll, Lα, Lβ and Lγ x-ray fluorescence cross-sections were measured for Ce, Pr and Sm at excitation energies of 14.94 and 17.44 keV using a low-energy Si(Li) detector coupled to a model 1024 computerized multi-channel analyser. Experimental results are compared with the theoretical estimates of Chen et al. based on relativistic Dirac-Hartree-Slater theory. Good agreement was observed between the experimental and theoretical values.

Elastic scattering and the associated anomalous dispersion in the energy range 8.63≤E≤42.75 keV from heavy atoms

Elastic scattering cross-sections for Pt, Au and Pb were measured using nearly monoenergetic unpolarized Kα x-ray photons in the energy range 8.63⩽E⩽42.75 keV at an angle of 90°. The experimental results were compared with theoretical elastic scattering cross-sections calculated using relativistic form factors (RFFs), relativistic modified form factors (RMFs), a combination of RFFs, RMFs with angle-independent anomalous scattering factors (ASFs) and relativistic numerical calculations based on the multipole expansion of the second-order S-matrix approach. The experimental results were in reasonable agreement with the S-matrix values and values based on an RMF+ASF approach compared with an RFF+ASF approach.

ELASTIC AND COMPTON SCATTERING CROSS SECTIONS IN THE ATOMIC REGION 12 Z 82

Abstract Coherent and Compton scattering cross sections for the elements Mg, Al, Mn, Ni, Cu, Y, Mod, Pd, Ag, Cd, In, Sn, Sb, Au and Pb have been measured at 32.06 keV (Ba Kα) and 33.29 keV (La Kα) x-ray energies. Measurements have been performed using an x-ray tube with a secondary excitor system as the excitation source instead of radioisotopes. 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. The present system reduced the scattering and background effects considerably and improved the monochromaticity. Experimental coherent scattering cross sections are compared with the normalised integrated coherent scattering cross sections. Experimental results are higher around the edges indicating the oscillatory nature of coherent intensity, resonance behaviour and fine structure effects. Experimental incoherent scattering cross sections are higher than the theoretical estimates for low medium Z elements and lower for heavy elements. The latter is due to the effect of electron binding at low photon energies for heavy elements.

L X-ray fluorescence cross sections, fluorescence yields and intensity ratios for Au and Pb at excitation energies 21.56, 31.64 and 34.17 keV

Abstract L l , L x , L β and L γ X-ray fluorescence cross sections and intensity ratios have been measured for the elements Au and Pb at the excitation energies 21.56, 31.64 and 34.17 KeV using an Si(Li) detector. Experimental fluorescence cross sections and intensity ratios are in good agreement with the theoretical estimates, calculated using the fluorescence yields and Coster-Kronig transition probabilities of Chen et al . (1981; Phys. Rev. A 24 , 177) based on relativistic Dirac-Hartree-Slater theory. Average L.-shell fluorescence yields are derived using experimental L X-ray fluorescence cross sections and theoretical photoionisation cross sections. Fluorescence yields are compared with the available results in the literature and also with the fitted values of Hubbell.