Conventional electron scattering and muonic atom spectroscopy techniques are challenging to apply to heavy ions unless the element has at least one stable or extremely long-lived isotope. To overcome this limitation, a recently introduced method for determining nuclear charge radii relies on extreme-ultraviolet (EUV) spectroscopy of the D1 line in highly charged Na-like ions. In this work, we present an experimental approach to measure the nuclear charge radii of isotopes of radioactive elements such as Fr, Ra, and Rn using this method at TRIUMF's Ion Trap for Atomic and Nuclear Science (TITAN) instrument, located at the ISAC radioactive beam facility. We also explore the potential of using Na-like D2 lines in the soft x-ray region for future measurements.

Context. Collisionally ionized plasmas produce X-ray spectra that depend on electron energy and atomic processes, requiring accurate atomic rate coefficients for modeling. While most data are theoretical, experimental measurements - such as those for Fe XXV - are critical for providing important benchmarks and quantifying uncertainties, thereby improving astrophysical spectral analysis, especially with high-resolution observatories like XRISM.Aims. This study aimed to experimentally measure the electron impact ionization (EII) cross section of Fe XXV, a key ion in astrophysical plasma diagnostics, and to evaluate the impact of these measurements on the interpretation of X-ray spectra from high-temperature plasma environments.Methods. The EII cross sections were measured using X-ray spectroscopy with an electron beam ion trap (EBIT) at various electron beam energies. The intensity ratios of the w resonance line in Fe XXV and the Ly alpha 1,2 lines in Fe XXVI were used to derive the cross sections. Level-resolved population calculations were performed using the NOMAD collisional-radiative code to account for processes affecting the emission ratios and ionization balance in the non-Maxwellian EBIT plasma.Results. The measured EII cross sections show good agreement with relativistic convergent close-coupling calculations. The uncertainties in the measurements, ranging from 8% to 12%, are discussed in terms of their impact on the accuracy of temperature diagnostics for astrophysical plasma environments.

Multiply charged ions with a single hole in closed shells are being extensively used to study relativistic and quantum electrodynamic (QED) effects due to the suppression of electron correlations in such systems. Here, we report measurements of the fine-structure splitting in the ground configuration 3d9 of Co-like ions of Yb, Re, Os, and Ir performed with an electron beam ion trap. Extensive relativistic many-body perturbation theory and multiconfiguration Dirac-Hartree-Fock calculations were executed with account of high-order QED contributions. It is found that those advanced calculations very well agree with the present accurate measurements of the 3d9 2D3/2 -2 D5/2 splittings. Comparisons with other theoretical works and experiments are presented as well.

We present spectral measurements performed to identify the highly-forbidden electric-octupole (E 3) 4 f7/2,5/2-5s1/2 transitions in Ag-like highly charged ions and to study the Z dependence of their intensities. Theoretical predictions indicate that these transitions can be observed in a narrow range of elements around tungsten (Z = 74), as the strong configuration interaction leads to level crossings and to an increased population of the 5s level. Here we probe the atomic structure and population dynamics in Ag-like ions using extreme-ultraviolet spectral measurements in several elements (Yb, Lu, W, Re, Os, Ir, Au) in the range Z = 70 to 79. The spectra were recorded independently in the compact electron-beam ion trap at the National Institute for Fusion Science and in the electron-beam ion trap at the National Institute of Standards and Technology. The measured wavelengths and the advanced theoretical calculations confirm observations of the E3 transitions in Ag-like ions in the predicted narrow element range.

We report measurements of the D1 and D2 transition energies in Na-like Ir (Ir66+). The D1 3s-3p1/2 transition energy, measured in the extreme ultraviolet (EUV) region at 169.977 +/- 0.005 eV with a relative uncertainty of 29 ppm, represents one of the most precise D-line energy measurements to date for high atomic numbers Z 30. The D2 3s-3p3/2 transition energy, measured in the x-ray region, is 621.11 +/- 0.06 eV. Therefore, there is a fine-structure separation of 451.13 +/- 0.06 eV for the Na-like Ir 3p levels. We present theoretical calculations of these energies using quantum electrodynamic-extended relativistic many-body perturbation theory and multipleconfiguration Dirac-Hartree-Fock methods, and discuss the discrepancies between experimental and theoretical values. The prospect of determining the absolute nuclear charge radii of heavy elements, including rare isotopes, from these measurements is explored.

Charge-exchange recombination with neutral atoms significantly influences the ionization balance in electron beam ion traps (EBIT) because its cross section is relatively large compared to cross sections of electron collision induced processes. Modeling the highly charged ion cloud requires the estimate of operating parameters, such as electron beam energy and density, the density of neutral atoms, and the relative velocities of collision partners. Uncertainty in the charge-exchange cross section can dominate the overall uncertainty in EBIT experiments, especially when it compounds with the uncertainties of experimental parameters that are difficult to determine. We present measured and simulated spectra of few-electron Fe ions, where we used a single charge-exchange factor to reduce the number of free parameters in the model. The deduction of the charge-exchange factor from the ratio of Li-like and He-like features allows for predicting the intensity of H-like lines in the spectra.

We report on a method for determining the absolute nuclear charge radius of high-Z elements using extreme-ultraviolet spectroscopy of highly charged Na-like ions in tandem with highly accurate atomic structure calculations of transition energy differences. The application of this method has reduced the nuclear charge radius uncertainty of 191Ir by a factor of 8 from the currently accepted literature value, with a recently reported charge radius of 5.442(12) fm. The result reduces the charge radius uncertainty along the full Ir isotopic chain when combined with prior optical isotope shift measurements. The technique utilizes only a few million ions stored in an ion trap, which should apply to measurements with small quantities of radioactive nuclei.

We show the effects of ladder ionization and hyperfine quenching on charge state distributions and spectral features of ions in electron beam ion trap (EBIT) devices. Ladder ionization with intermediate excitation of metastable states proceeds at lower than ionization potential electron beam energies, while hyperfine quenching reduces the lifetimes of these states by enhancing particular decay channels through nuclear-electronic coupling. Using Ni-like Pr and Nd ions, we show that these processes significantly alter ion populations and spectra, emphasizing the importance of incorporating hyperfine level specific modeling in EBIT studies.

Laser absorption spectroscopy provides high-resolution spectra of atomic transitions that reveal many often inaccessible features. The line shapes of krypton and xenon measured in magnetized plasmas are strongly affected by the contribution of the odd-numbered isotopes 83Kr, 129Xe and 131Xe due to their hyperfine structure, creating more challenging spectra in comparison to even-numbered ones. The lines originating from metastable levels of krypton and xenon with J = 2 (Kr I 760.4 nm) and J = 0 (Kr I 785.7 nm, Xe I 764.4 nm) were measured and analyzed in the linear plasma device PSI-2 in the field range of 22.5 mT-90 mT. Evaluating the Hamiltonian, including hyperfine and Zeeman interaction terms for these magnetic field strengths, unveils a deviation from the linear energy shift of the sublevels as a function of the magnetic field and from constant relative intensities that the weak field formulas provide. We prove that modeling the transitions in Xe using the weak field approximation, frequently used in magnetized plasma, becomes inadequate at approximate to 50 mT. In particular, the spectra of the 131Xe isotope show pronounced deviations from the weak field results. For krypton, however, the situation is less critical compared to xenon due to the low natural abundance of the odd-numbered isotope.

We describe a novel technique to determine absolute nuclear radii of high-Z nuclides. Utilizing accurate theoretical atomic structure calculations together with precise measurements of extreme ultraviolet transitions in highly charged ions this method allows for precise determinations of absolute nuclear charge radii based upon the well-known nuclear radii of their neighboring elements. This method can work for elements without stable isotopes, and its accuracy may be competitive with current methods (electron scattering and muonic x-ray spectroscopy).

Recent advance in calculations of energy levels of the 1s2$l$2$l^{\prime}$ core-excited states for ions along the Li isoelectronic sequence from carbon to uranium suggested that theoretical predictions for the 1s2$l$2$l^{\prime}$ transitions are significantly more precise than most of the experimental results available today and can thus be used for calibrating measured X-ray spectra. This suggestion is verified in the present work by comparison with benchmark experimental results. We present a critical compilation of all available experimental data on the energy levels of the 1s2$l$2$l^{\prime}$ core-excited states of Li-like ions. The compiled experimental data include uncertainty estimates, which allowed proper weighted averaging and comparison with theoretical calculations. This comparison confirmed the supremacy of the most advanced theoretical calculations of the 1s2$l$2$l^{\prime}$ levels over the best experimental results available today.

Extreme ultraviolet spectra from M-shell transitions in highly-charged Ca-like Nd 40+ through Na-like Nd 49+ ions were measured at the electron beam ion trap (EBIT) facility of the National Institute of Standards and Technology. To produce the ionization stages of interest, the electron beam energies were varied between 3.60 keV and 10.01 keV. A flat-field grazing incidence spectrometer was used to observe the spectra in the wavelength range between 2.67 nm and 17.30 nm. Simulated spectra generated with detailed collisional-radiative modeling of the non-Maxwellian EBIT plasma were used for line identifications. Forty-seven new spectral lines corresponding to electric-dipole and magnetic-dipole transitions were identified. Measurements were compared to the available previously calculated and predicted values.

AbstractThe building of online atomic and molecular databases for astrophysics and for other research fields started with the beginning of the internet. These databases have encompassed different forms: databases of individual research groups exposing their own data, databases providing collected data from the refereed literature, databases providing evaluated compilations, databases providing repositories for individuals to deposit their data, and so on. They were, and are, the replacement for literature compilations with the goal of providing more complete and in particular easily accessible data services to the users communities. Such initiatives involve not only scientific work on the data, but also the characterization of data, which comes with the “standardization” of metadata and of the relations between metadata, as recently developed in different communities. This contribution aims at providing a representative overview of the atomic and molecular databases ecosystem, which is available to the astrophysical community and addresses different issues linked to the use and management of data and databases. The information provided in this paper is related to the keynote lecture “Atomic and Molecular Databases: Open Science for better science and a sustainable world” whose slides can be found at DOI : doi.org/10.5281/zenodo.6979352 on the Zenodo repository connected to the “cb5-labastro” Zenodo Community (https://zenodo.org/communities/cb5-labastro).

In this paper, we present a detailed theoretical analysis of charge exchange recombination spectroscopy based on interactions of the planned ITER neutral beams (diagnostic beam of 100 keV u(-1) and heating beam of approximate to 1 MeV u(-1)) with highly-charged ions of tungsten. The results of the present spectral synthesis are based on the new set of nl-resolved charge exchange (CX) cross sections for recombination of the Wq+ ions (q = 61-66) with atomic hydrogen calculated using the classical trajectory Monte Carlo method. A large-scale collisional-radiative model describing the population kinetics of the high-n atomic states of Si-like through O-like W ions has been developed using the NOMAD code for typical conditions of the ITER core plasma, and the resulting spectra have been generated for wavelengths in the x-ray to visible range (0.1-1000 nm). A detailed analysis of the plasma emission predicts a significant effect of CX recombination on the W line intensity ratios that can be used for more advanced diagnostics of the ITER plasma.

The M-intrashell spectra from Co-like Yb43+ through Na-like Yb59+ ions produced in an electron beam ion trap (EBIT) at the National Institute of Standards and Technology have been studied in the extreme ultraviolet (EUV) range. A few N-intrashell transitions for Co-like Yb43+ and Fe-like Yb44+ are also reported. The EUV radiation was observed with a flat-field grazing incidence spectrometer in the wavelength region of about 7.5 nm to 26.2 nm. The electron beam energies were varied between 3.6 keV and 18 keV to produce the ionization stages of interest. The line identifications were based on the large-scale simulations of the EBIT plasma emission using the non-Maxwellian collisional-radiative code NOMAD. A total of 76 previously unobserved spectral lines corresponding to electric-dipole and magnetic-dipole transitions in the above mentioned ions were identified and discussed. In particular, our accurate wavelength of 24.3855 ± 0.0005 nm for a magnetic-dipole (M1) transition in the ground configuration of Co-like ion presents a solid benchmark for comparisons with the most advanced theories of atomic structure.

The electron-beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) was employed for the measurement and detailed analysis of the delta lambda(Xe-124, Xe-136) isotopic shifts of the Al-like 3s(2)3p P-2(1/2)-3s(2)3p P-2(3/2), Al-like 3s(2)3p (2)(P1/2)-3s(2)3d D-2(3/2), Mg-like 3s(2) S-1(0)-3s3p P-1(1), Mg-like 3s(2) S-1(0)-3s3p P-3(1), Na-like 3s(2) S-2(1/2) -3p P-2(1/2) (D-1), and Na-like 3s S-2(1/2)-3p P-2(3/2) (D-2) transitions. Systematic analysis revealed possible line blends and contributing experimental uncertainties. Highly accurate atomic-structure calculations were conducted and used to determine the delta < r(2)>(136,124) difference in the mean-square nuclear charge radii of the delta < r(2)>(136,124 )two xenon isotopes. In the present work, r(2) of 0.276 +/- 0.030 fm(2) was obtained from the weighted average of the Na-like D-1, Mg-like 3s(2)-3s3p and Al-like 3s(2)3p-3s(2)3p and 3s(2)3p-3s(2)3d transitions. This result confirms the value previously determined from the Na-like D-1 transition of 0.269 +/- 0.042 fm(2). The uncertainty of our result is half of that of previous results for the same isotopes obtained from x-ray spectroscopy of muonic atoms, laser spectroscopy of neutral xenon atoms, and a global evaluation of charge radii. Our result is slightly outside the uncertainty of the value obtained from a King plot analysis of comparable precision. The present work illustrates that extreme-ultraviolet spectroscopy of highly charged ions is a viable approach for measurements of charge nuclear radii differences and can be used to benchmark conventional methods.

We report on the results of the 10th Non-LTE code comparison workshop, which was held at the University of San Diego campus November 28 through December 1, 2017. Non-equilibrium collisional-radiative models predict the electronic state populations and attendant emission and absorption characteristics of hot, dense matter and are used to help design and diagnose high-energy-density experiments. At this workshop, fifteen codes from eleven institutions contributed results for steady-state and time-dependent neon, aluminum, silicon, and chlorine cases relevant to a variety of high-density experimental and radiation-driven astrophysical systems. This report focuses on differences in the predictions from codes with different internal structure, completeness, density effects, and rate fidelity and the impact of those differences on hot, dense plasma diagnostics.

Extreme ultraviolet spectra of highly-charged ytterbium ions produced in an electron beam ion trap at the National Institute of Standards and Technology were observed with a flat-field grazing incidence spectrometer in the wavelength region of about 4  nm–20  nm. The measured spectra were interpreted through detailed analysis by collisional-radiative modeling of the non-Maxwellian EBIT plasma. Seventy-nine new spectral lines due to intrashell (Δn = 0, n = 4) electric–dipole, magnetic–dipole, and electric–quadrupole transitions were identified in Rb-like Yb33+ through Ni-like Yb42+ ions. The effects of strong configuration interaction within the n = 4 complex on the measured spectra are discussed for a number of ionization stages.

We use narrow spectral lines from the X-ray spectra of various highly charged ions to measure low-energy tail-like deviations from a Gaussian response function in a microcalorimeter X-ray spectrometer with Au absorbers at energies from 650 to 3320 eV. We review the literature on low-energy tails in other microcalorimeter X-ray spectrometers and present a model that explains all the reviewed tail fraction measurements. In this model, a low-energy tail arises from the combination of electron escape and energy trapping associated with Bi X-ray absorbers.

We present spectroscopic measurements and detailed theoretical analysis of inner-shell LMn and LNn (n 4) dielectronic resonances in highly charged M-shell ions of tungsten. The x-ray emission from W49+ through W64+ was recorded at the electron-beam ion trap (EBIT) facility at the National Institute of Standards and Technology with a high-purity Ge detector for electron-beam energies between 6.8 and 10.8 keV. The measured spectra clearly show the presence of strong resonance features as well as direct excitation spectral lines. The analysis of the recorded spectra with large-scale collisional-radiative modeling of the EBIT plasma allowed us to unambiguously identify numerous dielectronic resonances associated with excitations of the inner-shell 2s1/2, 2p1/2, and 2p3/2 electrons.