The Kβ/Kα intensity ratios are critical parameters that quantitatively characterize atomic shell transition dynamics and radiative branching probabilities. In this study, we systematically evaluated the capability of machine learning (ML) algorithms to predict these ratios, as well as their advantages over traditional theoretical models (such as Scofield and semi-empirical calculations). A large dataset comprising 2124 experimental measurements compiled from the literature, covering elements with atomic numbers (Z) from 11 to 96, was structured to include more than ten variables, such as atomic number, sample form, excitation source, detector type, and energy resolution. Missing observations were imputed using the multivariate imputation by chained equations (MICE) method in the R programming language. Categorical variables were one-hot encoded, and the data were split into an 80% training set and a 20% test set. Seven heterogeneous individual models (RF, XGBoost, Cubist, SVR, GPR, BRNN, and GLMNET) were constructed, along with seven different stacking combinations derived from them. Following 10×10-fold cross-validation, the highest accuracy was achieved by the stacked model using a BRNN meta-learner (RMSE = 0.009; R2 = 0.973). This model reduced the test error of the Scofield theory by nearly 48% and performed significantly better according to the Diebold-Mariano test (p < 0.001). SHAP analysis revealed that atomic number is the primary determinant, while sample purity and excitation source have secondary yet physically consistent effects. Furthermore, an online R/Shiny-based calculator enhances the practical applicability of the method by enabling users to input their experimental parameters and receive instantaneous Kβ/Kα predictions. These results demonstrate that at the current stage of theoretical and experimental development, data-driven approaches provide significant advantages in both accuracy and interpretability over classical theories for complex atomic parameters such as the Kβ/Κα intensity ratio. Overall, this work constitutes a significant step toward reducing deviations in high-Z elements, improving detector calibration, and establishing new atomic databases.

This work presents a comprehensive analytical investigation of Coster-Kronig transition probabilities f12, f13, f23, F1, and F123 for elements with atomic numbers 28 <= Z <= 98. Experimental data from our previous studies were systematically compiled and employed to construct smooth empirical trends by polynomial interpolation so as to represent the variation of these transitions across the different elements. In parallel, new theoretical values were calculated for selected elements using the Multiconfiguration Dirac-Fock (MCDF) method, incorporating relativistic effects. When compared with available theoretical and experimental data the results show good agreement, especially for medium and heavy elements. These new results provide reliable reference data for modeling L-shell vacancy decay processes and support a range of applications in atomic physics, X-ray spectroscopy, and radiation interaction studies.

In this study, we use the relativistic multiconfiguration Dirac-Fock method (MCFD) to compute the probabilities of radiative and radiationless vacancy transfer from K- to L-1-,L- L2-, and( L3_) subshells in S-16, Ar-18, Ti-22, Cu-29, Zn-30, Ge-32, As-33, Se-34, Kr-36, Zr-40, Cd-48, Sn-50, Te-52, Hg-80, Bi-83, and( 86)Rn atoms. Semi-theoretical calculations for elements within the atomic range of 18 < Z < 96 (Ar-18 to( 96)Cm) were also conducted, leveraging available data on radiative and radiationless transitions from the scientific literature. The theoretical calculation results aligned well with the values calculated semi-theoretically and with other published works. However, some notable differences were identified.

X-ray spectra linewidths have been measured in Nb, Mo, and Rh. From the obtained experimental values, the K , L 2 , and L 3 level widths were estimated and compared with the recommended and semi-empirical values, as well as our theoretical results.

This work presents a comprehensive analytical investigation of Coster–Kronig transition probabilities , , , , and for elements with atomic numbers . Experimental data from our previous studies were systematically compiled and employed to construct smooth empirical trends by polynomial interpolation so as to represent the variation of these transitions across the different elements. In parallel, new theoretical values were calculated for selected elements using the Multiconfiguration Dirac–Fock (MCDF) method, incorporating relativistic effects. When compared with available theoretical and experimental data the results show good agreement, especially for medium and heavy elements. These new results provide reliable reference data for modeling L-shell vacancy decay processes and support a range of applications in atomic physics, X-ray spectroscopy, and radiation interaction studies.

K alpha 1,2, L alpha 1,2, and L beta 1 X-ray spectra linewidths have been measured in elements Nb, Mo, and Rh, using a high-resolution double-crystal X-ray spectrometer. From the obtained experimental values, Gamma K, Gamma L2, and Gamma L3 level widths were estimated and compared with the recommended and semi-empirical ones, and our theoretical results. The overall tendency of the corrected full width at half maximum of the K alpha 1 and K alpha 2 lines as a function of Z agrees with the data in the literature.

An investigation of Cu Kα X-ray emission spectra, together with their satellite lines, using both experimental techniques and theoretical calculations, provides accurate values for the natural linewidths and other parameters of the emission lines.

The knowledge of atomic fundamental parameters, such as the fluorescence yields with low uncertainties, is of decisive importance in elemental quantification involving X-ray fluorescence analysis techniques. However, especially for the low-Z elements, the available literature data are either of poor quality, of unknown or very large uncertainty, or both. For this reason, the K-shell fluorescence yield of carbon was determined in the PTB laboratory at the synchrotron radiation facility BESSY II. In addition, theoretical calculations of the same parameter were performed using the multiconfiguration Dirac-Fock method, including relativistic and quantum electrodynamics (QED) corrections. Both values obtained in this work are compared to the corresponding available literature data.

Kα,β X-ray lines from photon excitation were measured in selected elements from Mg to Cu using a high-resolution double-crystal X-ray spectrometer with a proportional counter, and the Kβ/Kα intensity ratio for each element was obtained, after correcting for self-absorption, detection efficiency, and crystal reflectance. This intensity ratio increases rapidly from Mg to Ca but, in the 3d elements region, the increase becomes slower. This is related to the intensity of the Kβ line involving valence electrons. The slow increase of this ratio in the 3d elements region is thought to be due to the correlation between 3d and 4s electrons. Moreover, the chemical shifts, FWHM, asymmetry indices, and Kβ/Kα intensity ratios of the Cr compounds, due to different valences, were also investigated using the same double-crystal X-ray spectrometer. The chemical effects were clearly observed, and the Kβ/Kα intensity ratio was found to be compound-dependent for Cr.

In this work, we present K- and L- shell fluorescence yield values of the full isonuclear sequence of Fe ions, using a state-of-the-art multiconfiguration Dirac–Fock approach. These results may be of importance for spectral fitting and plasma modeling, both in laboratory and astrophysical studies, where Fe is an important benchmark element. The K-shell fluorescence yields were found to be very similar up to the removal of 14 electrons.

We present relativistic ab initio calculations of fundamental parameters for atomic selenium, based on the Multiconfiguration Dirac-Fock method. In detail, fluorescence yields and subshell linewidths, both of K shell, as well as Kβ to Kα intensity ratio are provided, showing overall agreement with previous theoretical calculations and experimental values. Relative intensities were evaluated assuming the same ionization cross-section for the K-shell hole states, leading to a statistical distribution of these initial states. A method for estimating theoretical linewidths of X-ray lines, where the lines are composed by a multiplet of fine-structure levels that are spread in energy, is proposed. This method provides results that are closer to Kα1,2 experimental width values than the usual method, although slightly higher discrepancies occur for the Kβ1,3 lines. This indicates some inaccuracies in the calculation of Auger rates that have a higher contribution for partial linewidths of the subshells involved in the Kβ1,3 profile. Apart from this, the calculated value of Kβ to Kα intensity ratio, which is less sensitive to Auger rates issues, is in excellent agreement with recommended values.

In this work, we present fluorescence yield and width values of Ne‐, Ar‐, and Kr‐like ion levels for selected values of Z, using a state‐of‐the‐art multiconfiguration Dirac–Fock approach. The results may be useful for the interpretation of spectra from plasmas, in both laboratory and astrophysics, as well as from ion collision experiments.

We report on measurements of the Kβ diagram, valence‐to‐core (VtC), and hypersatellite X‐ray spectra induced in metallic Cr by photon single and double K‐shell ionization. The experiment was carried out at the Stanford Synchrotron Radiation Lightsource using the seven‐crystal Johann‐type hard X‐ray spectrometer of the beamline 6‐2. For the Kβ diagram and VtC transitions, the present study confirms the line shape features observed in previous works, whereas the Khβ hypersatellite transition was found to exhibit a complex spectral line shape and a characteristic low‐energy shoulder. The energy shift of the hypersatellite relative to the parent diagram line was deduced from the measurements and compared with the result of extensive multiconfiguration Dirac–Fock (MCDF) calculations. A very good agreement between experiment and theory was found. The MCDF calculations were also used to compute the theoretical line shape of the hypersatellite. A satisfactory agreement was obtained between the overall shapes of the experimental and theoretical spectra, but deviations were observed on the low‐ and high‐energy flanks of the hypersatellite line. The discrepancies were explained by chemical effects, which were not considered in the MCDF calculations performed for isolated atoms.

We provide, for the first time to our knowledge, accurate theoretical data for the the transition energy and probability values related to the decay of the most important excited states in He- through C-like lanthanum and cerium ions leading to the emission of K X-ray lines. We employed the multiconfiguration Dirac-Fock method, including QED corrections, to obtain the wave functions and energy values of each level involved in the X-ray analyzed transitions. The presented data may be used, among others, in the diagnostic of laboratory plasmas, such as the ones obtained in EBIT and ECRIS sources.

Spectra emitted by highly ionized tungsten atoms from magnetically confined plasmas show a common feature: a narrow structured quasi-continuum emission band most prominent in the range 4−7 nm, which accounts for 40−80% of the radiated power. This band has been fairly well explained by unresolved transitions from groups 4d-4p, 4f-4d (Δn = 0) and 5d-4f, 5g-4f and 5p-4d (Δn = 1). In this work we use a Multi-Configuration Dirac-Fock code in Breit self-consistent field mode to compute level energies and transition probabilities for W27+ to W37+ ions contributing to this emission band. Intra-shell correlation was introduced in the calculation for both initial and final states and all dipole and quadrupole radiative transitions have been considered. The wavefunctions in the initial and final states are optimized separately and the resulting non-orthogonality effect is fully taken into account. The importance of some satellite lines was assessed. Together with the ionic distributions obtained by using the FLYCHK application and assuming that the initial states population depends statistically on the temperature we were able to synthesize plasma emission spectrum profiles for several electron temperatures.

A low-cost facility, able to simulate icing conditions occurring in flight, has been built via modification of a small blow-down supersonic wind tunnel. As the storage tank (30bar) is emptied through the wind tunnel, expansion of the contained air makes temperature to decrease down to -20 degrees C and a control valve holds such temperature for about 200s. In order to increase the liquid water content (LWC) of the flow allowing ice formation on model surfaces within the test chamber, water is sprayed in the stream within the stagnation chamber by means of a controlled spray gun. This unsteady technique allows to work only at a peculiar Mach number at which the heating from the tank walls compensates the cooling due to expansion. Both an Icing Rotating Cylinder and an Icing Blade Technique have been used to measure the LWC in the stream. The Median Volumetric Diameter (MVD) of the supercooled water drops has been measured by both a Phase Doppler Particle Analyzer (PDPA) and an Oil Slide Technique. The measured values of the LWC ranged from 0,7 to 1,5 g/m(3) and those of the MVD ranged from 20 to 50 mu m in accordance with typical values encountered in flight within dangerous clouds.

A new method is described which is capable of determining \ensuremath{\Vert}\ensuremath{\Delta}${\mathrm{E}}_{0\mathrm{\ensuremath{-}}1}$\ensuremath{\Vert}, the absolute value of the fine-structure splitting of the interval ${2}^{3}$${\mathrm{P}}_{0}$-${2}^{3}$${\mathrm{P}}_{1}$ from the hyperfine quenched lifetime of the ${2}^{3}$${\mathrm{P}}_{0}$ state of heliumlike ions with nuclear spin. Based on this method a measurement is reported of \ensuremath{\Vert}\ensuremath{\Delta}${\mathrm{E}}_{0\mathrm{\ensuremath{-}}1}$\ensuremath{\Vert} in the heliumlike ion $^{107}$${\mathrm{Ag}}^{45+}$ with the result \ensuremath{\Vert}\ensuremath{\Delta}${\mathit{E}}_{0\mathrm{\ensuremath{-}}1}$\ensuremath{\Vert}=0.${74}_{\mathrm{\ensuremath{-}}0.19}^{+0.16}$ eV. The error in the measurement is substantially smaller than the natural linewidth of 1.1 eV.