Measurement of K-L radiative vacancy transfer probabilities in selected rare earth elements bombarded with 3-4 MeV protons

K-shell X-ray intensity ratios for selected rare earth elements were measured following irradiation with proton beams having energies between 3 and 4 MeV. Using the X-ray intensity ratios, the radiative vacancy transfer probabilities from the shell K to the L sub-shells were determined. The experimental data were compared to theoretical predictions for X-ray line intensities and radiative vacancy transfer probabilities. The results showed a good agreement between theory and experiment.     

A simple theoretical approach to multiple ionization and its application for 5.1 and 5.5 MeV/u Xq++ Ne collisions

The simple geometrical model we developed recently for ionization probabilities on the basis of a geometrical BEA picture is generalized and extended to take into account magnetic substates and non-zero impact parameter ion-atom collisions. Ionization probabilities per electron for the L shell and separately for the 2s and 2p Subshells of neon in 5.1 MeV/u N⁺ and N⁷⁺ as well as 5.5 MeV/u H⁺ collisions were determined from 0.8−1 eV resolution K-Auger spectra. Anisotropy parameters of KL-LL₂₃L₂₃ satellite lines were determined in 5.5 MeV/u Ar⁶⁺, Ne¹⁰⁺ and 5.1 MeV/u N²⁺ collisions. The comparison of the extended model with the experimental data shows a good agreement. The model seems to be able to give account of the dependence of the ionization probability on quantum numbers l and m. Comparing the results with a wide range of experimental data no contradictions were found with the universal scaling features predicted by the model. By analyzing the impact parameter dependence of ionization probabilities the validity of the model was estimated to break down at ν₁ ≈ ν₂/3 towards lower impact velocities.     

Energy shifts of L x-rays from 70 ⩽ Z ⩽ 90 elements due to multiple M vacancies

The transition energies of L x-rays for states with 0–11 M-shell spectator vacancies are calculated by using a Dirac-Fock computer program. The calculations are done for seven elements with atomic numbers in the 70 ⩽ Z ⩽ 90 range. In each of these elements, the transition energies of 10 L x-rays (L_l, L_α2, L_α1, L_η, L_β1, L_γ1, L_γ2, L_γ3, L_γ4′, L_γ4) are calculated as differences of average-of-configuration energies. The energy shifts of these x-rays for various multiple M vacancy states are deduced from the transition energies and plotted as a function of atomic number.     

Vacancy properties in gold

A detailed, multi-parameter fitting analysis has been performed on the experimental data available for self-diffusion, equilibrium vacancy concentrations and effective vacancy migration energies, obtained from direct observations of vacancy precipitation after quenching, in gold. The ranges of allowed values for the various vacancy activation enthalpies were determined, within realistic experimental uncertainty limits, to be 0.89 ? E^F_1V ? 0.96 eV, 0.25 ? E^B_2v ? 0.57 eV, 0.83 ? E^M_1V ? ? 0.89 eV, 0.62 ? E^M_2V ? 0.79 eV and 0.48 ? E^M_3v ? 0.56 eV. Limits were also obtained for the various pre-exponential or entropy factors. Since within these limits correlations among the possible parameter values exist, the results of the combined analyses are presented as fields in parameter-space. The value of this type of fitting procedure for deducing vacancy defect properties from experiment is discussed. A representative set of allowed vacancy parameters was used to computer-model a quench and subsequent recovery. These calculations demonstrated the self-consistency of the assumption of local equilibrium for the analyses of these vacancy precipitation results.     

Analytical formulas for ionization cross sections and coster-kronig corrected fluorescence yields of the L1, L2, and L3 subshells

We present analytical formulas for three L-subshell ionization cross sections for proton impact based on the recent experimental data and for the Coster-Kronig corrected fluorescence yields based on the theoretical values due to Chen et al. and due to McGuire. Total L X-ray production cross sections were calculated using the analytical formulas and compared with experimental values. As a result, our semi-empirical values using the formulas fitted to the values of Chen et al. coincided with the experimental values very well. Furthermore our values for L_α, L_β, L_γ, L_η, and L_l X-ray production cross sections calculated using the analytical L1, L2, and L3 Subshell ionization cross sections, and the theoretical values of the fluorescent yields and of the Coster-Kronig transition probabilities due to Chen et al. also agreed with the experimental values.     

The roles of Pauli correlations,channel couplings,and shake-off in ion- induced KLv and K2Lv multiple-vacancy production

Cross sections for target K-plus-L-shell multiple-vacancy production by ions can be inferred from experimental measurements of K X-ray and Auger satellite intensities. The theory of KⁿL^v multiple-vacancy distributions has been generalized from the single-particle model (the statistically independent electron approximation) to the independent Fermi particle model. The Pauli correlations (electron exchange terms) are found to nearly cancel in many cases because of a tendency toward random phases. This results in the first quantal demonstration that the vacancy distribution is nearly binomial (but slightly narrower). Calculations have been generalized from the traditional first-order approximations to unitary approximations (first Magnus and coupled-channels) which correctly predict the saturation of the mean vacancy probability with increasing projectile charge. The recent availability of satellite and hypersatellite data for the same collision system makes possible the beginning of an investigation of the effects of increased removal energies and increased shaking in hypersatellites (K²L^v) as compared with satellites. We review our unified treatment of ion-plus-shaking induced amplitudes for L-vacancy production accompanying ion-generated K-holes. Calculations for C⁶⁺ +Ne satellite and hypersatellite vacancy distributions are presented.     

Formation and properties of defects and small vacancy clusters in SiC: Ab initio calculations

Large-scale ab initio simulation methods have been employed to investigate the configurations and properties of defects in SiC. Atomic structures, formation energies and binding energies of small vacancy clusters have also been studied as a function of cluster size, and their relative stabilities are determined. The calculated formation energies of point defects are in good agreement with previously theoretical calculations. The results show that the di-vacancy cluster consists of two C vacancies located at the second nearest neighbor sites is stable up to 1300 K, while a di-vacancy with two Si vacancies is not stable and may dissociate at room temperature. In general, the formation energies of small vacancy clusters increase with size, but the formation energies for clusters with a Si vacancy and nC vacancies (V_Si-nV_C) are much smaller than those with a C vacancy and nSi vacancies (V_C-nV_Si). These results demonstrate that the V_Si-nV_C clusters are more stable than the V_C-nV_Si clusters in SiC, and provide possible nucleation sites for larger vacancy clusters or voids to grow. For these small vacancy clusters, the binding energy decreases with increasing cluster size, and ranges from 2.5 to 4.6 eV. These results indicate that the small vacancy clusters in SiC are stable at temperatures up to 1900 K, which is consistent with experimental observations.     

Internal conversion coefficients for E5 and M5 nuclear transitions, 30 ≤ Z ≤ 104

Presented here are internal conversion coefficients (ICC) for E5- and M5-multipolarities of nuclear gamma rays for 75 values of atomic number Z in the range 30 ≤ Z ≤ 104. The tables provide the missing data for E5 and M5 transitions in the Hager and Seltzer tables. These tables contain M-shell ICC, which those of Sliv and Band do not, and are calculated in a better atomic field (Hartree-Fock-Slater). The calculations are relativistic with finite nuclear size effect taken into account. K-shell ICC for 20 values of the transition energy up to 6 MeV, L-subshell ICC for 25–26 values of the transition energy up to 2 MeV, and M-subshell ICC for 18 values of the transition energy up to ≈0.2 MeV are given.     

Wavelengths,transition probabilities,and oscillator strengths for M-shell transitions in Co-, Ni-, Cu-, Zn-, Ga-, Ge-, and Se-like Au ions

Wavelengths, transition probabilities, and oscillator strengths have been calculated for M-shell electric dipole transitions in Co-, Ni-, Cu-, Zn-, Ga-, Ge-, and Se-like Au ions. The fully relativistic multiconfiguration Dirac–Fock method, taking quantum electrodynamical effects and the Breit correction into account, was used in the calculations. Calculated energy levels of M-shell excited states for Cu-, Zn-, Ga-, Ge-, and Se-like Au ions from the method were compared with available theoretical and experimental results, and good agreement with them was achieved.     

Oxygen detection by non-Rutherford proton backscattering below 2.5 MeV

Oxygen detection by proton backscattering has been investigated. The oxygen detection sensitivity of 2.5 MeV proton backscattering is shown to exceed that of ⁴He backscattering by even a factor of about 15 depending on the matrix. The needed proton elastic scattering cross sections of oxygen for θ_lab = 170° have been measured in the energy range E_lab = 770–2480 keV relative to Ti and Sn elastic scattering cross sections using thin TiO₂ and SnO₂ samples. The angular dependence of the cross section was measured at energies E_lab = 1790, 1990, 2191, and 2382 keV for backscattering angles. The experimental cross sections were found to be 1.1–5.7 times the pure Coulomb cross section. Theoretical calculations for the scattering cross sections were performed and their inapplicability to experimental purposes is demonstrated. Fits to experimental data are given.     

Interface current method for PHWR cluster geometry with anisotropy in the angular flux at interfaces

A method based on combination of interface current formalism and first-flight probabilities was previously developed for solving the integral transport equation for cylindricalized lattice cells of pressurized heavy-water reactors (PHWRs), where only double-P₀ expansions (i.e. isotropic angular flux) were considered for the angular flux at various interfaces. It was found necessary to choose the correct mesh-spacing in the moderator to get good results. In order to resolve this problem, we have considered the anisotropy in the angular flux by expanding it in spherical harmonics in two half-spaces (double-P_N or DP_N approximation). Terms up to P₂ expansion can be considered in it. The results of present method in one-group and 27-groups, under various approximations of angular flux, have been compared with the exact collision probability (P_ij) method for clusters by using the same mesh-spacing in the moderator for both methods. It is found that the results corresponding to DP₁ expansion of angular flux agree well with the P_ij method. However, results corresponding to DP₂ expansion can be taken as standard. Even with this, the computer time taken is very much less compared to the P_ij method.     

Atomic electron binding energies

Recent experimental atomic electron binding-energy determinations for the gaseous or vapor and condensed elemental states are compared in Table I for elements with Z < 31 and for a number of levels in several heavier elements. Also entered for comparison are the corresponding atomic electron binding-energy values from Table II, an extension of the original Bearden and Burr tabulation of electron binding-energy determinations for the elements in the condensed state. From the comparison one can determine which of the Table II values are for the elemental state.Chemical and physical shifts in atomic electron binding energies are briefly considered.Table II presents for elements of atomic number Z = 1 to Z = 106 the atomic electron binding energies for the K-, L-, M-, and N-shells, and for the O_1–5- and P_1–3-subshells. Comparisons of these values with the theoretical values of Huang et al. are presented in graphical form. Interpolation and extrapolation procedures are employed to fill in missing electron binding-energy values. In arriving at these account has been taken of the results of Bearden and Burr, most of them based on least-squares adjustment of overdetermined values, and of new measurements published up to January 1978 in the fields of x-ray emission and absorption spectrometry and of photo- and Auger-electron spectrometry.     

中等重原子L壳层空位的退激模型和L_1次壳层空位的衰变率(英文)

本文系统地叙述了中等重元素原子L壳层空位的退激模型,并求得了这些元素的L_1次壳层能级宽度、荧光产额、M电子Shakeoff几率、L_1-L_2M_(4.5)和L_1-L_3M_(4,5)跃迁产额等物理量。     

Fast ion collisions with C60 in vapour phase and collective excitation: Comparison with other gaseous targets

The single and double ionization of a free C₆₀ molecule in collisions with fast heavy (F and Si) ions is investigated using a recoil ion time-of-flight mass spectrometer. The projectile charge state (q_p) dependence has also been investigated. A linear q_p-dependence has been explained in terms of a plasmon excitation model. In addition, continuum electron spectroscopy has been used to detect the electron emission from fullerenes. The measured electron angular distribution for the fullerene target is compared with that for a gaseous target at a fixed electron energy. The ratio of forward-to-backward cross section for C₆₀ is quite different from that for Ne.     

Measurement of L X-ray fluorescence cross-sections for elements with 45 ? Z ? 50 using synchrotron radiation at 8 keV

The L shell fluorescence cross-sections of the elements in range 45 ? Z ? 50 have been determined at 8 keV using Synchrotron radiation. The individual L X-ray photons, Ll, Lα, Lβ_I, Lβ_II, Lγ_I and Lγ_II produced in the target were measured with high resolution Si(Li) detector. The experimental set-up provided a low background by using linearly polarized monoenergetic photon beam, improving the signal-to-noise ratio. The experimental cross-sections obtained in this work were compared with available experimental data from Scofield [1] and [2] Krause [3] and [4] and Scofield and Puri et al. [5] and [6].These experimental values closely agree with the theoretical values calculated using Scofield and Krause data, except for the case of Lγ, where values measured of this work are slighter higher.     

Relative intensities for Li (i = 1-3) and Mi (i = 1-5) subshell X-rays

The intensities for L_i (i = 1-3) subshell X-ray lines have been computed relative to the most intense line in each series, for elements with 30 ? Z ? 92, from published X-ray emission rates based on the Dirac-Fock (DF) model. In the case of M_i (i = 1-5) subshell X-ray lines, complete sets of emission rates based on both the Dirac-Hartree-Slater and the DF models have been generated for elements with 65 ? Z ? 92 by logarithmic interpolation of the data available for a limited number of elements. The intensities for different M X-ray lines have been computed relative to the most intense line in each series using these two sets of emission rates. The L_i (i = 1-3) and M_i (i = 1-5) subshell X-ray relative intensities computed from the DF model based emission rates have been least-squares-fitted to polynomials in the atomic number for use in software packages for quantitative elemental analysis using X-ray emission techniques and for other applications.     

Proton induced L-shell X-ray production cross-sections for Pb in the energy range 225–400 KeV

The L-shell X-ray production cross-sections in lead (Pb) by proton impact over the energy range 225–400 keV, with an interval of 25 keV, have been measured. The thick target X-ray yields have been obtained using a HPGe detector. The experimental results for σ_L1, σ_Lα, σ_Lβ and σ_Lγ have been compared with perturbed stationary state theory with relativistic (R), energy loss (E) and Coulomb (C) corrections (ECPSSR theory). The comparison of L_α, L_β and L_γ, X-ray production cross-sections shows a fairly good agreement, except at the lowest energy. The L₁ X-ray production cross-sections are higher by ≈ 20–30% than their theoretical estimates.