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Register a new userCalculations for electron-impact excitation and ionization of beryllium
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The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudo-state and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the $(2s2p)^3P$ and $(2s2p)^1P$ states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications.
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Neutral tungsten is the primary candidate as a wall material in the divertor region of the International Thermonuclear Experimental Reactor (ITER). The efficient operation of ITER depends heavily on precise atomic physics calculations for the determination of reliable erosion diagnostics, helping to characterise the influx of tungsten impurities into the core plasma. The following paper presents detailed calculations of the atomic structure of neutral tungsten using the multiconfigurational Dirac-Fock method, drawing comparisons with experimental measurements where available, and includes a critical assessment of existing atomic structure data. We investigate the electron-impact excitation of neutral tungsten using the Dirac R-matrix method and, by employing collisional-radiative models, we benchmark our results with recent Compact Toroidal Hybrid measurements. The resulting comparisons highlight alternative diagnostic lines to the widely used 400.88nm line.
There are major discrepancies between recent B-spline R-matrix (BSR) and Dirac Atomic R-matrix Code (DARC) calculations regarding electron-impact excitation rates for transitions in Mg$^{4+}$, with claims that the DARC calculations are much more accurate. To identify possible reasons for these discrepancies and to estimate the accuracy of the various results, we carried out independent BSR calculations with the same 86 target states as in the previous calculations, but with a different and more accurate representation of the target structure. We find close agreement with the previous BSR results for the majority of transitions, thereby confirming their accuracy. At the same time the differences with the DARC results are much more pronounced. The discrepancies in the final results for the collision strengths are mainly due to differences in the structure description, specifically the inclusion of correlation effects, and due to the likely occurrence of pseudoresonances. To further check the convergence of the predicted collision rates, we carried out even more extensive calculations involving 316 states of Mg$^{4+}$. Extending the close-coupling expansion results in major corrections for transitions involving the higher-lying states and allows us to assess the likely uncertainties in the existing datasets.
We present benchmark integrated and differential cross-sections for electron collisions with H$_2$ using two different theoretical approaches, namely, the R-matrix and molecular convergent close-coupling (MCCC). This is similar to comparative studies conducted on electron-atom collisions for H, He and Mg. Electron impact excitation to the $b ^3Sigma_u^+$, $a ^3Sigma_g^+$, $B ^1Sigma_u^+$, $c ^3Pi_u$, $EF ^1Sigma_g^+$, $C ^1Pi_u$, $e ^3Sigma_u^+$, $h ^3Sigma_g^+$, $B ^1Sigma_u^+$ and $d ^3Pi_u$ excited electronic states are considered. Calculations are presented in both the fixed nuclei and adiabatic nuclei approximations, where the latter is shown only for the $b ^3Sigma_u^+$ state. Good agreement is found for all transitions presented. Where available, we compare with existing experimental and recommended data.
A theoretical investigation of the dissociative excitation by electron impact on the NO molecule is presented, aiming to make up for the lack of data for this process in the literature. A full set of vibrationally-resolved cross sections and corresponding rate coefficients are calculated using the Local-Complex-Potential approach and five resonant states of NO^-.
Using TRIUMFs off-line laser ion source test stand with a system of tunable titanium sapphire lasers, the polarization dependence of laser resonance ionization has been investigated using beryllium. A significant polarization dependence was observed for the excitation path $^1$S$_0$$rightarrow$$^1$P$^{circ}_1$$rightarrow$$^1$S$_0$, which are typical transitions for alkaline and alkaline-like elements. This polarization dependence was further verified on Be radioactive isotopes at TRIUMFs isotope separator and accelerator facility (ISAC). Laser polarization was proven to be an important parameter in operating resonance ionization laser ion sources (RILIS). The polarization spectroscopy was preformed off-line both on the 2p$^2$ $^1$S$_0$ autoionizing (AI) state and high-$n$ Rydberg states of the $2sns$ $^1S_0$ and $2snd$ $^1D_2$ series. The energy of the 2p$^2$ $^1$S$_0$ AI state and ionization potential (IP) of beryllium were extracted as 76167(6)~cm$^{-1}$ and 75192.59(3)~cm$^{-1}$. Polarization spectroscopy can be used to determine the $J$ values of newly found states in in-source spectroscopy of the complex/radioactive alkaline-like elements such as Ra, Sm, Yb, Pu and No.
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