Measurement of L x-ray production cross sections by 60 keV photons and average L shell fluorescence yields of lanthanides

L x-ray production cross sections have been measured for lanthanides with 60 keV. The measured L x-ray production cross section values for the lanthanides are in good agreement with the theoretical ones evaluated using L _i subshell fluorescence yields ω_i, Coster-Kronig transition probabilities ? _ij based on the Relativistic-Hartree-Slater theory, K to L _i subshell vacancy transfer probabilities n _KLi, fractions of the ratiative width of the subshell F _ny and L _i subshell photoionisation cross section σ_Pi. The average L shell fluorescence yields ω_L have also been derived using the presently measured total L x-ray production cross section values and the theoretical K to L shell vacancy transfer probabilities. These results are compared with theoretically predicted values.     

Measurement of L subshell fluorescence yields of some elements in the atomic range 75⩽Z⩽92 using photoionization

L subshell fluorescence yields (ω₁, ω₂ and ω₃) for the elements Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Th and U have been measured at the 123.6 keV γ-ray emission excitation energy from a ⁵⁷Co annular radioactive source (925 MBq) using a Si(Li) detector. The measured L subshell fluorescence yields were compared with the theoretical and semi-empirical values.     

Measurement of vacancy transfer probabilities from K to L shell for high atomic number elements

The probabilities for vacancy transfer from K to L shell, η_KL, were obtained by measuring the K_β/K_α intensity ratios in 25 elements over the range 57 ≤ Z ≤ 92 using a 25 mCi ⁵⁷Co filtered source for excitation. The K X-rays were measured by using a Si(Li) detector. The theoretical values were calculated via the radiative and radiationless transition rates of these elements. The comparison between present experimental results and theoretical predictions showed that both results agreed well. The experimental and theoretical values were fitted against atomic number (Z). The measured values of η_KL for Tm, Yb, Lu, Hf and Ir are being reported here for the first time.     

Kβ/Kα X-ray intensity ratios for elements in the range 16⩽Z⩽92 excited by 5.9, 59.5 and 123.6 keV photons

The K shell intensity ratios K_β/K_α for 59 elements in the atomic region 16⩽Z⩽92 have been measured at excitation energies of 5.9, 59.5 and 123.6 keV. K X-rays emitted by samples have been counted by a Si(Li) detector with resolution 160 eV at 5.9 keV. The measured values were compared with the theoretical values calculated using Scofield's tables based on the Hartree–Slater and Hartree–Fock theories and available experimental values. Reasonable agreement is typically obtained between present and theoretical values.     

Measurement of K shell fluorescence cross sections and K shell fluorescence yields for the atomic region 22≤Z≤64 by 59.5 keV photons

A new method has been developed to determine K shell fluorescence cross section and K shell fluorescence yields. This method is based on simultaneous measurement of fluorescence radiation and scattered radiation, thus avoiding problems with measuring the source strength and source-to-detector solid angle. The K shell fluorescence cross section and K shell fluorescence yield for 21 elements in the atomic range 22£Z£64 have been measured by using a Si(Li) detector. The obtained results are compared with the other experimental, theoretical and fit values.     

K X-ray satellites of uranium bombarded with 500 MeV neon

K X-ray satellite spectra produced during the bombardment of uranium with 500 MeV neon, have been investigated with a high resolution crystal spectrometer. The experimental results are compared with theoretical predictions for vacancy production computed in the semiclassical separate atom perturbation theory and corrected forL subshell coupling and electron transfer from targetL shell into projectileK shell. The agreement between theory and experiment is rather good. It turns out, that the reduction ofL vacancy production due toL subshell coupling is essentially compensated by theL electron transfer from target to projectile. The present work is an extension of a previous study of theK α₁ satellite spectra of tantalum bombarded with 403 MeV nitrogen.     

Measurements ofL-subshell fluorescence yields for light and medium heavy elements (28≤Z≤47)

We report on the first determination ofL-subshell fluorescence yields, ω_Li, for various elements with 28≤Z≤47. The method applied is based on the subshell ionization by relativistic electron impact with an electron energy ofE ₀=50 keV and the detection of characteristic X rays by means of a high resolution crystal spectrometer calibrated absolutely with respect to its transmission and reflectivity. The number of initialL vacancies and its subshell distribution as well as the normalized X-ray transition probabilities, the Coster-Kronig yields and theK-shell Auger transition rates are taken from theory. The results obtained for ω_Li yield values that are for all three subshells in agreement with the predictions of a widely used semi-empirical formula and for ω _L2 and ω _L3 also with theoretical calculations. The values of ω _L1, however, exceed the theory systematically.     

Determination of K shell X-ray intensity ratios for some heavy elements

The K shell X-ray intensity ratios K_α2/K_α1, K_β1,3/K_α1 and K_β2/K_α1 for 21 elements with 65⩽Z⩽92 have been measured using an incident photon energy of 123.6 keV. The X-rays have been measured with a Si(Li) semiconductor detector. K_β and K_α X-rays have been analyzed into the components K_β1,3 and K_β2 and K_α1 and K_α2, respectively, using a computer program. The experimental results were compared with the theoretical values of Scofield and available experimental results. All X-ray intensity ratios values have been plotted versus atomic number.     

Chemical effects on L shell fluorescence yields of Ba, La and Ce compounds

Chemical effects on the average L shell fluorescence yields (v_L) for Ba, La and Ce compounds were investigated. Samples were excited by gamma-rays with 59.5 keV energy photons from a ²⁴¹Am radioisotope source. L X-rays emitted by samples were counted by a Si(Li) detector with a resolution 155 eV at 5.9 keV. Chemical effects on the average L shell fluorescence yield (v _L) for Ba, La and Ce compounds were observed. The values are compared with theoretical and experimental ones for the pure elements.     

Calculation of vacancy transfer probabilities from K to L shell using the X-ray fluorescence parameters

The probabilities for vacancy transfer from the K to the L shell (η_KL), have been calculated for eleven high atomic number elements using the measured K and L shells X-ray production cross-sections. The targets were excited by 123.6 keV photon from a ⁵⁷Co annular radioactive source. K and L X-rays emitted by samples were counted with a Si(Li) detector. The measured values of η_KL were compared with the theoretical values and our early papers.     

Energy dependence of photon-induced Kα and Kβ x-ray production cross-sections for some elements with 38≤Z≤51 in the energy range 20–50 keV

The energy dependence of photon-induced Kα and Kβ x-ray production (or x-ray fluorescence) cross-sections for Sr, Y, Mo, Ru, Pd, Ag, In and Sb elements has been studied in the energy range of 20–50 keV using Energy Dispersive X-Ray Fluorescence (EDXRF) Spectrometry. The photon energy dependence of K x-ray production cross-sections was measured with secondary excitation method. A radioisotope point source of ²⁴¹Am was employed to excite the K x-rays of secondary exciter elements. The L x-ray yields from Th and U were measured to determine I_oG (the intensity of exciter K x-rays falling on primary target). The measurements have been made by observing the x-ray emissions with the help of HPGe detector coupled with a multichannel analyzer. The areas of the Kα and Kβ spectral peaks, as well as the net peak areas, have been determined by a fitting process. The measured Kα and Kβ x-ray production cross-sections have been compared with calculated theoretical values in this energy regime. The present experimental results for all the elements were in general agreement with the theoretical values calculated using photoionization cross-sections, fractional rates (based on Hartree–Slater potentials) and fluorescence yields.     

Measurement of L subshell photoionisation cross sections of Th and U at 22.6, 25.8, 29.2 and 32.9 kev

Bremsstrahlung from an X-ray tube was used to excite secondary targets of Ag, Sn, I and Ba to get nearly monochromatic excitation energies of 22.6, 25.8, 29.2 and 32.9 keV, respectively. Th and U were used as targets. The L X-ray fluorescence cross sections of different lines from the targets have been measured. Of the several methods to obtain L subshell photoionisation cross sections from these fluorescence data, the merits and demerits of four common methods have been explained and the method with least uncertainty was suggested as the best one for such analysis. Following this method, with intensities of the resolved L_γ lines, three L subshell photoionisation cross sections have been obtained using six different sets of atomic parameters. The variation of these cross sections with different atomic parameters has been discussed. For σ₁, all the derived values are within 30% of one other while for σ₂ and σ₃, they are within 12%. Measured cross sections have been compared with the data of others and with the theoretical values of Scofield. Finally, the intensity ratios of different L lines have also been compared with available data and the theoretical values. Within experimental errors, our data are in good agreement with the data of others and with the theoretical predictions.     

K shell,L shell–subshell and M shell–subshell photoeffect cross-sections in elements between Tb (Z=65) and U (Z=92) at 123.6 keV

In this paper, we report on measurements of K shell, L shell–subshell and M shell–subshell photoeffect cross-sections for 21 high-atomic-number elements between Tb (Z=65) and U (Z=92) at 123.6 keV. These photoeffect cross-sections have been measured by using our earlier measurements of the K-shell X-ray production cross-sections. The measured photoeffect cross-sections have been compared with calculated theoretical values. It is clear that the results compare well with theoretical values within an experimental average error. At 123.6 keV, these cross-sections have been measured for the first time. The results have been plotted versus atomic number.     

Phase stability and chemical composition dependence of the thermoelectric properties of the type-I clathrate Ba8AlxSi46−x (8≤x≤15)

Phase stability of the type-I clathrate compound Ba₈Al_xSi_46−x and the thermoelectric property dependence on chemical composition are presented. Polycrystalline samples were prepared by argon arc melting and annealing. Results of powder X-ray diffraction and electron microprobe analysis show that the type-I structure is formed without framework deficiency for 8≤x≤15. Lattice constant a increases linearly with the increase of x. Thermoelectric properties were measured for x=12, 14 and 15. The Seebeck coefficients are negative, with the absolute values increasing with x. The highest figure of merit zT=0.24 was observed for x=15 at T=1000 K, with carrier electron density n=3×10²¹ cm⁻³. A theoretical calculation based on the single parabolic band model reveals the optimum carrier concentration to be n∼4×10²⁰ cm⁻³, where zT∼0.7 at T=1000 K is predicted.     

YBa2Cu3O7 electro-magnetic optic effects in Ba L2,3 X-ray absorption near Tc

The onset of electro-magnetic optic effects, observed at the Ba L_2,3 edges synchrotron X-ray absorption by a YBa₂Cu₃O₇ single crystal, 20 K above the transition temperature to superconductivity, T_c ∼ 92 K is used to identify the role played by the Ba donor layer in the transition to superconductivity in the CuO₂ layers. Negative permeability leads to Faraday rotation of the transmitted beam below T = 112 to 56 K for the 22 μm thick single crystal (c-axis orientation of 8π/18 relative to ε_X-rays) and sharp changes in the density of empty final states lead to zero transmitted radiation in an interval ΔE at the given orientation. The temperature dependence: ΔE(L₂) = 1.4, 3.5 and 3.9 eV, while ΔE(L₃) = 5.3, 6 and 7 eV at T = 92, 74 and 63 K, respectively, indicates that the width of the empty final states bands increases as T decreases. ΔE(L₃)/ΔE(L₂) = 3.8 at 92 K to 1.8 at 63 K also indicates that the d_5/2 symmetry bands fill faster than those of d_3/2 symmetry below T_c, providing the first experimental evidence of unpaired spin-orbit states in the Ba donor layer of a superconductor. These effects, characteristic of ferromagnetic and anti-ferromagnetic materials near a resonance absorption, signal the onset of a Mott transition. The interaction between the layer states is described using 1D conjugate molecular orbitals.     

Measurements of radiative vacancy transfer probabilities from L3 subshells to M,N and O shells and subshells in the atomic range 72⩽Z⩽92

The probabilities of vacancy transfer, η_L3M, ηL₃M₁, ηL₃M₄, ηL₃M₅, η_L3N, ηL₃N₁, ηL₃N₄, ηL₃N₅, ηL₃O₁ and ηL₃O_4,5 from L₃ subshell to M, N and O shells and subshells for the elements Hf, Ta, W, Re, Pt, Au, HgO, Tl, Pb, Bi, Th, U have been measured using L shell fluorescence yields and X-ray intensity ratios. These experimental values were obtained from samples excited by 59.5-keV γ-rays, which were emitted from an ²⁴¹Am radioisotope source. Also K and L X-rays emitted from samples were measured by means of Si(Li) detector with a resolution of 155 at 5.9 keV. The results obtained from this study are compared with the results of other studies.     

Mξ, Mαβ, Mγ and Mm X-ray production cross-sections for elements with 71⩽z⩽92 at 5.96 keV photon energy

The M_ξ, M_αβ, M_γ and M_m X-ray production (XRP) cross-sections have been measured for the elements with 71⩽Z⩽92 at 5.96 keV incident photon energy satisfying E_M1<E_inc<E_L3, where E_M1(L3) is the M₁(L₃) subshell binding energy. These XRP cross-sections have been calculated using photoionization cross-sections based on the relativistic Dirac–Hartree–Slater (RDHS) model with three sets of X-ray emission rates, fluorescence, Coster–Kronig and super Coster–Kronig yields based on (i) the non-relativistic Hartree–Slater (NRHS) potential model, (ii) the RDHS model and (iii) the relativistic Dirac–Fock (RDF) model. For the third set, the M_i (i=1–5) subshell fluorescence yields have been calculated using the RDF model-based X-ray emission rates and total widths reevaluated to incorporate the RDF model-based radiative widths. The measured cross-sections have been compared with the calculated values to check the applicability of the physical parameters based on different models.     

Determination of the enthalpy of fusion of K3TaF8 and K3TaOF6

The areas of the fusion and crystallization peaks of K₃TaF₈ and K₃TaOF₆ have been measured using the DSC mode of the high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities and the temperature dependence of the used calorimetric method sensitivity, the values of the enthalpy of fusion of K₃TaF₈ at temperature of fusion 1039 K: Δ_fusH_m(K₃TaF₈; 1039 K) = (52 ± 2) kJ mol⁻¹ and of K₃TaOF₆ at temperature of fusion 1055 K: Δ_fusH_m(K₃TaOF₆; 1055 K) = (62 ± 3) kJ mol⁻¹ have been determined.     

Composition and structure of acid leached LiMn2−yTiyO4 (0.2≤y≤1.5) spinels

Lithium manganese titanium spinels, LiMn_2−yTi_yO₄, (0.2≤y≤1.5) have been synthesized by solid-state reaction between TiO₂ (anatase), Li₂CO₃ and MnCO₃. Li⁺ was leached from the powdered reaction products by treatment in excess of 0.2 N HCl at 85 °C for 6 h, under reflux. The elemental composition of the acidic solution and solid residues of leaching has been determined by complexometric titration, atomic absorption spectroscopy and X-ray fluorescence analysis. Powder X-ray diffraction was used for structural characterization of the crystalline fraction of the solid residues. It has been found that the amount of Li⁺ leached from LiMn_2−yTi_yO₄ decreases monotonically with increasing y in the interval 0.2≤y≤1.0 and abruptly drops to negligibly small values for y>1.0. The content of Mn and Li in the liquid phase and of Mn and Ti in the solid (amorphous plus crystalline) residue, were related to the composition and cation distribution in the pristine compounds. A new formal chemical equation describing the process of leaching and a mechanism of the structural transformation undergone by the initial solids as a result of Li⁺ removal has been proposed.