Energy levels and spectral lines of tungsten, W III through W LXXIV

The energy levels and spectral lines of multiply ionized tungsten atoms, W²⁺ through W⁷³⁺, have been compiled. Experimental data on spectral lines and energy levels exist for the spectra of W III through W VII, W XXVIII through W LI, W LIII, and W LV through LXV. For W VIII, the four lowest energy levels were derived from the series limits of W VII. For W LXIV (Na-like) and W LVI (K-like), we supplement experimental data on energy levels and wavelengths with predicted values found by accurate interpolations and extrapolations along the isoelectronic sequences. For W LXXIII (He-like) and W LXXIV (H-like), theoretical data on energy levels and line wavelengths are compiled. For W III, we include experimentally determined radiative transition probabilities where available. The ground state configurations and terms were determined for all stages of ionization. A value of ionization energy is included for each ion.     

Measurements of the W values in argon,nitrogen, and methane for 0.93 to 5.3 MeV alpha particles

The W values in argon, nitrogen and methane have been measured for alpha particles with energies from 0.93 MeV to 5.3 MeV by gridded ionization chambers. The energies of alpha particles emitted from ²¹⁰Po (5.3 MeV) were reduced by passage through Al foils and Mylar films of various thicknesses. The mean energies of these “reduced” alpha particles were determined using a silicon detector calibrated with five natural alpha sources. The W values for the gases and energies studied are obtained by assuming a W value of 26.31 eV in pure argon for 5.3 MeV alpha particles. The W value in argon is found to be slightly dependent on the energy of alpha particles. In nitrogen and methane, the W values for an alpha energy of 0.93 MeV are about 5 and 8% larger, respectively, than for an alpha energy of 5.3 MeV.     

Atomic data and theoretical X-ray spectra of Ge-like through V-like W ions

The atomic structure and spectra of ten tungsten ions have been calculated using the Flexible Atomic Code. The calculations yield energy levels, radiative lifetimes, spectral line positions, transition probability rates, and oscillator strengths for the tungsten ions isoelectronic to germanium, W⁴²⁺${}^{42+}$, through vanadium, W⁵¹⁺${}^{51+}$. Collisional–radiative models for high-temperature, low-density plasmas have been implemented to produce line emissivities for X-ray transitions in the 1–4 keV (3–12 Å) spectral interval. The Ge-like through V-like W ions are important in nuclear fusion research where their spectra may provide diagnostic information on magnetically confined plasmas.     

He+ (np) cross sections for 2, 3, 4 and 5 MeV C4+ ions colliding with He atoms

The cross sections of ionization plus excitation of He are measured by the C⁴⁺ + He prototype reaction with energies ranging from 2 to 5 MeV. Theoretically the independent electron approximation is used to calculate the HeII (np) ionization plus excitation cross sections. The results of the calculations are compared with our experimental data.     

Radiative recombination rate coefficients for highly-charged tungsten ions

Partial and total radiative recombination rate coefficients are presented for highly-charged ions of tungsten with closed shells, W²⁸⁺, W³⁸⁺, W⁴⁶⁺, W⁵⁶⁺, W⁶⁴⁺, W⁷⁰⁺, and W⁷²⁺, as well as for the H-like ion W⁷³⁺ and the bare nucleus W⁷⁴⁺. The temperature range is considered. Calculations have been performed in the framework of the fully relativistic Dirac-Fock treatment of photoionization and radiative recombination processes taking into account all significant multipoles of the radiation field. We assess the influence of multipole effects on recombination rate coefficients as compared with the commonly used dipole approximation. For the first time, we show that the relativistic Maxwell-Boltzmann distribution of continuum electrons should be used at high temperature. This decreases the rate coefficient significantly compared to the nonrelativistic distribution.     

Energy levels,radiative rates,and lifetimes for transitions in W XL

Energy levels and radiative rates are reported for transitions in Br-like tungsten, W XL, calculated with the general-purpose relativistic atomic structure package (grasp). Configuration interaction (CI) has been included among 46 configurations (generating 4215 levels) over a wide energy range up to 213 Ryd. However, for conciseness results are only listed for the lowest 360 levels (with energies up to ∼43 Ryd), which mainly belong to the 4s²4p⁵,4s²4p⁴4d,4s²4p⁴4f,4s4p⁶,4p⁶4d,4s4p⁵4d,4s²4p³4d², and 4s²4p³4d4f configurations, and provided for four types of transitions, E1, E2, M1, and M2. Comparisons are made with existing (but limited) results. However, to fully assess the accuracy of our data, analogous calculations have been performed with the flexible atomic code, including an even larger CI than in grasp. Our energy levels are estimated to be accurate to better than 0.02 Ryd, whereas results for radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions.     

Theoretical energy level spectra and transition data for 4p4d, 4p4d4f,and 4p4d configurations of W

The ab initio   quasirelativistic Hartree–Fock method developed specifically for the calculation of spectral parameters of heavy atoms and highly charged ions is used to derive transition data for a multicharged tungsten ion. The configuration interaction method is applied to include electron correlation effects. The relativistic effects are taken into account in the Breit–Pauli approximation for quasirelativistic Hartree–Fock radial orbitals. The energy level spectra, radiative lifetimes and Lande g$g$-factors are calculated for the 4p⁶4d², 4p⁶4d4f, and 4p⁵4d³ configurations of the ion W³⁶⁺. The transition wavelengths, spontaneous transition probabilities, oscillator strengths, and line strengths for the electric dipole, electric quadrupole, electric octupole, and magnetic dipole transitions among the levels of these configurations are tabulated.     

Issues from activation/dose rates calculation for full W ITER machine and increased fluence

The paper presents and discusses the results of the activation calculations for ITER to investigate the effect of a possible increase of the neutron fluence on the First Wall (FW) and of the use of tungsten instead of beryllium as inboard and outboard FW protective layer. The new analyses based on the recent ITER design have been performed using the most recent, reliable and validated nuclear data and codes. Three situations have been considered: (1) average FW neutron fluence of 1.0 MWa/m² with beryllium FW protective layers (PLs); (2) average FW neutron fluence of 0.5 MWa/m² with tungsten FW PLs and (3) average FW neutron fluence of 1.0 MWa/m² with tungsten FW PLs.The used approach considers the Scalenea-1 radiation transport sequence for obtaining the 175 groups neutron fluxes in all the materials/zones on the radial direction of the ITER equatorial midplane and the EASY2007 code package for the material activation analysis. For tungsten PLs, calculations have also been performed using a MCNP approach in a 1D geometry. In this way the effect of the multi-group treatment of cross-sections is compared versus a continuous energy treatment and the deriving self-shielding effect is determined in the case of W where many resonances are present.     

Single- and multiple-electron loss cross-sections for fast heavy ions colliding with neutrals: Semi-classical calculations

Extensive calculations of single, multiple and total electron-loss cross-sections of fast heavy ions in collisions with neutral atoms are performed in the semi-classical approximation using the DEPOSIT code based on the energy deposition model and statistical distributions for ionization probabilities. The results are presented for Ar¹⁺, Ar²⁺, Kr⁷⁺, Xe³⁺, Xe¹⁸⁺, Pb²⁵⁺ and U^q+ (q = 10, 28, 39, 62) ions colliding with H, N, Ne, Ar, Kr, Xe and U atoms at energies E > 1 MeV/u and compared with available experimental data and the n-particle classical-trajectory Monte Carlo (nCTMC) calculations. The results show that the present semi-classical model can be applied for estimation of multiple and total electron-loss cross-sections within accuracies of a factor of 2.From calculated data for the total electron-loss cross-sections σ_tot, their dependencies on relative velocity v, the first ionization potential I₁ of the projectile and the target atomic number Z_A are found and a semi-empirical formula for σ_tot is suggested. The velocity range, where the semi-classical approximation can be used, is discussed.     

Energy levels,radiative rates,and lifetimes for transitions in W LVIII

Energy levels and radiative rates are reported for transitions in Cl-like W LVIII. Configuration interaction (CI) has been included among 44 configurations (generating 4978 levels) over a wide energy range up to 363 Ryd, and the general-purpose relativistic atomic structure package (grasp) adopted for the calculations. Since no other results of comparable complexity are available, calculations have also been performed with the flexible atomic code (fac), which help in assessing the accuracy of our results. Energies are listed for the lowest 400 levels (with energies up to ∼98 Ryd), which mainly belong to the 3s²3p⁵, 3s3p⁶, 3s²3p⁴3d, 3s²3p³3d², 3s3p⁴3d², 3s²3p²3d³, and 3p⁶3d configurations, and radiative rates are provided for four types of transitions, i.e. E1, E2, M1, and M2. Our energy levels are assessed to be accurate to better than 0.5%, whereas radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions.     

The energy levels and radiative transition probabilities for electric quadrupole and magnetic dipole transitions among the levels of the ground configuration, [Kr]4d4f, of W

Large-scale multiconfiguration Hartree-Fock and Dirac-Fock calculations have been performed for the ground configuration, [Kr]4d¹⁰4f⁴, energy levels of the W²⁴⁺ ion. The relativistic corrections were taken into account in the quasirelativistic Breit-Pauli and fully relativistic Breit (taking into account QED effects) approximations. The role of correlation, relativistic, and QED corrections is discussed. Line strengths, oscillator strengths, and transition probabilities in the Coulomb and Babushkin gauges are presented for the electric quadrupole (E2) transitions among these levels. The magnetic dipole transitions are also investigated. Dependence of the E2 transition probabilities on the gauge condition of the electromagnetic field potential is studied as well.     

Fragmentation of water on swift He ion impact

Charge exchange and fragmentation are the usual results in ion-molecule collision systems, and the specifics of the fragmentation process determine the chemical destiny of the target system. In this paper, we report recent progress on calculations of the fragmentation patterns for the model system He²⁺ + H₂O for projectile energies of a few keV. The calculations are obtained using the electron-nuclear dynamics (END) method for solution of the time-dependent Schrödinger equation.     

Investigation of plasma exposed W–1% La2O3 tungsten in a high ion flux,low ion energy,low carbon impurity plasma environment for the International Thermonuclear Experimental Reactor

Previous investigations of tungsten for the International Thermonuclear Experimental Reactor (ITER) were focusing on using energetic ion beams whose energies were over 1 keV. This study presents experimental results of exposed W–1% La₂O₃ in high ion flux (10²² m^–2), low ion energies (about 110 eV) steady-state deuterium plasmas at elevated temperatures (873–1250 K). The tungsten samples are floating during plasma exposure. Using a high-pressure gas analyzer, the residual carbon impurities in the plasma are found to be about 0.25%. No carbon film is detected on the surface by the EDX analysis after plasma exposure. An infrared pyrometer is also used as an in situ detector to monitor the surface emissivities of the substrates during plasma exposure. Using the scanning electron microscopy, microscopic pits of sizes ranging from 0.1 to 5 μm are observed on the plasma exposed tungsten surfaces. These pits are believed to be the results of erupted deuterium gas bubbles, which recombine underneath the surface at defect locations and grain boundaries, leading to substrate damage and erosion loss of the substrate material. Low temperature plasma exposure of a tungsten foil indicates that deuterium gas (D₂) is trapped inside the substrate. Macroscopic blisters are observed on the surface. The erosion yield of the W–1% La₂O₃ increases with temperature and seems to saturate at around 1050 K. Scattered networks of bubble sites are found 5 μm below the substrate surface. High temperature plasma exposure appears to reduce the population as well as the size of the pits. The plasma exposed W–1% La₂O₃ substrates, exposed above 850 K, retain about 10¹⁹ D/m², which is two orders of magnitude less than those retained by the tungsten foils exposed at 400 K.     

Radioactive tungsten in the atmosphere

As a result of thermonuclear tests carried out by the United States in 1958, radioactive tungsten isotopes W¹⁸¹ and W¹⁸⁵ appeared in the atmosphere. Determination of the W¹⁸¹ and W¹⁸⁵ concentrations by means of a -spectrometer and -counter, respectively, made it easily possible to determine the date of formation of these products. The geographic distribution of the radioactive tungsten concentrations is basically the same as that of fission fragment products but the residence time of tungsten in the stratosphere was found to be much shorter than that of fission fragment products. This may be due to the size and weight of the aerosols from which tungsten was deposited. The total activity of the radioactive tungsten ejected into the stratosphere was estimated at 900 MCi.Translated from Atomnaya Énergiya, Vol. 13, No. 6, pp. 572–575, December, 1962     

An L2 representation of the continuum in collisions between alpha particles and lithium atoms

We report new theoretical results obtained in close-coupling calculations within the impact parameter method, using two-centred AO expansions with an extended L² basis for charge transfer, target excitation, and ionisation in collisions between H²⁺ and Li. The basis is chosen by demanding a good representation of oscillator strengths for dipole transitions both to excited and to ionised levels. The calculations bring the theoretical and experimental total cross sections for single-electron capture between 40 and 200 keV lab. close together. They also reproduce accurately the Li(2p) excitation cross sections over a wide energy range. The first close-coupling estimate of ion-impact ionisation of Li is also given. Preliminary results suggest that an important contribution to the ionisation cross sections at intermediate energies may come from transitions to d- and f-states of the target continuum.     

Theoretical energy level spectra and transition data for 4p4d, 4p4f and 4p4d configurations of W ion

The ab initio quasirelativistic Hartree-Fock method developed specifically for the calculation of spectral parameters of heavy atoms and highly charged ions was applied to determine atomic data for tungsten ions. The correlation effects were included by adopting the configuration interaction method. The Breit-Pauli approximation for quasirelativistic Hartree-Fock radial orbitals was employed to take into account relativistic effects. The energy level spectra, radiative lifetimes, Lande factors g were calculated for the 4p⁶4d, 4p⁶4f and 4p⁵4d² configurations of W³⁷⁺ ion. The atomic data, namely, the transition wavelengths, spontaneous emission rates and oscillator strengths for the electric dipole, electric quadrupole and magnetic dipole transitions among and within the levels of these configurations are tabulated.     

Excitation energies, radiative and autoionization rates, dielectronic satellite lines, and dielectronic recombination rates for excited states of Na-like W from Ne-like W

Energy levels, radiative transition probabilities, and autoionization rates for and states in Na-like tungsten (W⁶³⁺) are calculated. Cowan’s relativistic Hartree-Fock method, the relativistic multiconfiguration method implemented in the Hebrew University Lawrence Livermore Atomic Code, and the relativistic many-body perturbation theory method, are used. Autoionizing levels above the threshold 1s²2s²2p⁶ are considered. It is found that configuration mixing plays an important role for all atomic characteristics. Also strong mixing between states with 2s and 2p holes (1s²2s²2p⁵3l₁nl₂+1s²2s2p⁶3l₃nl₄) occurs. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the excited states. It is shown that the contribution of the highly excited states is very important for calculation of total DR rates. Contributions from the autoionizing states and to the DR rate coefficients are estimated by extrapolation of all atomic parameters. The orbital angular momentum (l) distribution of the rate coefficients shows a peak at l=2. The total DR rate coefficient is derived as a function of electron temperature. The dielectronic satellite spectra of W⁶³⁺ are important for L-shell diagnostics of very high-temperature laboratory plasmas such as future ITER fusion plasmas.     

K X-ray emission induced by C and O ion impact on selected lanthanoids

Measurements of K-shell X-ray production cross sections by ¹²C⁴⁺ (beam energies between 12 MeV and 14 MeV), and ¹⁶O⁵⁺ ions (with energies between 12.5 MeV and 15 MeV) are presented. The target elements were selected lanthanoids (Ce, Gd, Dy, Ho and Er). The resulting measurements are evaluated through comparisons with the eECPSShsR-UA theory, the MECPSSR model and the adiabatic perturbation (also known as direct molecular orbital, MO) theory, using a scaling based on the reduced velocity parameter . Consideration is given to multiple ionization effects and electron capture contribution to K-shell ionization. An evaluation with previously published values is also given. It is shown that the behavior of the ratios of experimental to theoretical cross sections is different for both ions. The models do not seem to be accurate to predict the X-ray production cross sections for ¹²C⁴⁺ ions, while the MECPSSR theory predicts much better the experimental data for ¹⁶O⁵⁺ than the eECPSShsR-UA.     

Overview of the US–Japan collaborative investigation on hydrogen isotope retention in neutron-irradiated and ion-damaged tungsten

The effect of neutron-irradiation damage has been mainly simulated using high-energy ion bombardment. A recent MIT report (PSFC/RR-10-4, An assessment of the current data affecting tritium retention and its use to project towards T retention in ITER, Lipschultz et al., 2010) summarizes the observations from high-energy ion bombardment studies and illustrates the saturation trend in deuterium concentration due to damage from ion irradiation in tungsten and molybdenum above 1 displacement per atom (dpa). While this prior database of results is quite valuable for understanding the behavior of hydrogen isotopes in plasma facing components (PFCs), it does not encompass the full range of effects that must be considered in a practical fusion environment due to short penetration depth, damage gradient, high damage rate, and high primary knock-on atom (PKA) energy spectrum of the ion bombardment. In addition, neutrons change the elemental composition via transmutations, and create a high radiation environment inside PFCs, which influences the behavior of hydrogen isotope in PFCs, suggesting the utilization of fission reactors is necessary for neutron-irradiation. Under the framework of the US–Japan TITAN program, tungsten samples (99.99 at.% purity from A.L.M.T. Co.) were irradiated by fission neutrons in the High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory (ORNL), at 50 and 300 °C to 0.025, 0.3, and 2.4 dpa, and the investigation of deuterium retention in neutron-irradiated tungsten was performed in the Tritium Plasma Experiment (TPE), the unique high-flux linear plasma facility that can handle tritium, beryllium and activated materials. This paper reports the recent results from the comparison of ion-damaged tungsten via various ion species (2.8 MeV Fe²⁺, 20 MeV W²⁺, and 700 keV H^?) with that from neutron-irradiated tungsten to identify the similarities and differences among them.     

Mass Spectrometric Study of Ions Formed from Cesium Metaborate Vapor under Electron Impact

An ionization behavior of cesium metaborate vapor under electron impact has been studied by a mass spectrometric method. Formations of Cs²⁺, CsB⁺, CsO⁺, Cs⁺ ₂, Cs₂O⁺, B⁺ and BO^? ₂ ions have been identified in addition to the well known ions of Cs⁺, CsBO⁺, CsBO⁺ ₂ and Cs₂BO⁺ ₂. Ionization processes and vapor precursors for these ions have been given from ionization efficiency curves, appearance energies, temperature dependence of ion intensities and energetics of the ionization processes as follows: the process for the formations of Cs⁺ with AE(Cs⁺)=3.9± 1.0 eV and BO^? ₂ ions is the ion pair formation from CsBO₂(g), that for CsBO⁺ ₂ ion is the simple ionization of CsBO₂(g), that for Cs⁺ with AE (Cs⁺) =9.1±0.5 eV, Cs²⁺, CsBO⁺, CsB⁺, CsO⁺ and B⁺ ions is the dissociative ionization from CsBO₂(g) and that for Cs⁺ ₂, Cs₂O⁺ and Cs₂BO⁺ ₂ ions is the dissociative ionization from Cs₂(BO₂)₂(g). The knowledge of the ionization behavior of cesium metaborate vapor under electron impact is very useful in the mass spectrometric study of vaporization behaviors of CsBO₂(s) and simulated radioactive waste borosilicate glasses.