Foil Excitation Research Articles

Combined effect of cascade through circular orbits and Stark quenching on the decay of n=2→n=1 transition of H-like Fe in beam–foil excitation

Recently Mishra et al. (Mishra AP, et al. J Quant Spectrosc Radiat Transf 2013;120:114–9), while analyzing the effects of cascading through circular orbits (l=n−1)on the decay of unresolved 2p,2s→1s transitions of H-like Fe, neglected the effect of electric field at the exit surface of foil on the lifetime of the 2s state. In the present work we have considered the combined effect of cascading through circular orbits and the Stark mixing on the decay of the 2p,2s→1s transitions of H-like Fe in beam–foil excitation. It is observed that the natural lifetime of the 2s state (350.6ps) is reduced to 221.8±22.4ps due to Stark mixing of the long-lived 2s2S1/2 state with the very close and short-lived 2pP1/2o2 state. The strength of the electric field responsible for such mixing comes out to be 7.09±0.37×106V/cm. The results of the present work for cascading of circular orbits through the 2p state are in good agreement (within the error bars) with those obtained earlier by Mishra et al.

Effect of cascade through circular Rydberg states and surface wakefield on the decay of n=2→n=1 transition of H-like V in beam–foil excitation

Beam–foil spectroscopy is used to study the unresolved decay of short-lived 2p (τ2p≈5.3fs) and long-lived 2s (τ2s≈756.7ps) states of H-like V for the time range 25–400ps. We have observed a hump-like structure, peaked at ~145ps, in the decay of the 2p state riding on the decay curve of the 2s state. This unusual behavior is similar to the one reported by us recently in H-like Fe (Mishra AP, et al. J Quant Spectrosc Radiat Transfer 2013;120:114–9) and occurs as a consequence of the sequential cascading down of circular Rydberg states to the 2p state. More importantly, it is inferred in this paper that Nandi and Mohanty (Nandi T, Mohanty BP. J Phys B: At Mol Opt Phys 2009;42:225402), who attributed the drastic reduction in the observed lifetime of the 2s state in beam-foil excitation to Stark mixing of the 2s2S1/2 and 2p2P1/20 states due to the wakefield at the exit surface of the foil, had overestimated the Stark mixing parameter and the strength of the wake electric field responsible for the mixing at least by a factor ~5.5.

Coherent beam–foil excitation of 2s1/2 and 2p1/2 states of hydrogen and antihydrogen atoms in an external electric field

A beam–foil experiment is proposed for observation of a phase shift π in a beat intensity of light emitted by hydrogen and antihydrogen atoms in an external electric field. This effect is based on the existence of the terms linear in the electric field in the expression for the radiation probability of an atom. The linear terms have an opposite sign for hydrogen and antihydrogen atoms and lead to such a difference in a beat signal. Experimental conditions for observation of this effect are discussed.

Access to Two-Photon QED Contributions via 2s 2S1/2–2p 2P1/2 Transitions in Heavy Li-Like Ions

Wavelengths of the 2s 2S1/2–2p 2P1/2 fine structure transition in lithium-like ions in the medium heavy Z range have been measured using beam foil excitation and grazing incidence spectroscopy. The achieved precision of 70 ppm allows for a 0.1% QED test which establishes a new benchmark. It provides sensitivity to two-photon QED contributions. Very good agreement with the newest calculations based on hydrogenic wave functions and applying a strict QED formalism is observed. All accurate published data along the isoelectronic Li-like series for Z > 20 are summarized. Their values and their accuracies are compared to the calculations and to the relative QED contributions, respectively.

Measurements of2s2S1/2–2p2P1/2transition energies in lithiumlike heavy ions. III. Experimental results forSn47+andXe51+

Wavelengths of the fine-structure transition $2s{}^{2}{S}_{1/2}$--$2p{}^{2}{P}_{1/2}$ in lithiumlike ${\mathrm{Sn}}^{47+}$ and ${\mathrm{Xe}}^{51+}$ have been determined using beam foil excitation and grazing incidence spectroscopy. Transition wavelengths of $114.895\ifmmode\pm\else\textpm\fi{}0.008 \AA{}$ for ${\mathrm{Sn}}^{47+}$ and $103.475\ifmmode\pm\else\textpm\fi{}0.007 \AA{}$ for ${\mathrm{Xe}}^{51+}$ have been measured. While there has been no previous measurement of this transition in Sn, the Xe result marks an improvement in accuracy of more than an order of magnitude compared with previous experiments. The achieved precision of 70 ppm for the 1/2-1/2 transition allows for a 0.1% QED test which establishes a new benchmark for Li-like ions in the medium Z range. The experimental uncertainty is smaller than the size of the smallest calculated contribution to the transition energy.

Improvement in the reliability of lifetime measurements for highly charged ions in the 0.01–100-ns range

We report here the finding that, to obtain reliable lifetimes in highly ionized atoms measured by beam foil excitation, the conditions must be set so that the charge state studied is well below the average charge of the foil emergent beam. If this condition is not fulfilled, the decay curves may be significantly distorted by blending with close-lying satellite lines. We present evidence to show that failures to follow this criterion have led to serious underestimates in reported lifetimes in isoelectronic line strength studies. We also suggest guidelines for avoiding these distortions in future measurements.

Measurement of 2s–2p Transition Energies in Few Electron Heavy Ions

We have measured 2s–2p fine structure transition energies in highly charged Ni, Zn, and Ag ions using beam–foil excitation and grazing incidence spectroscopy at the GSI–UNILAC accelerator. The precision of the results provides tests of two-photon QED screening corrections to the 2s–2p transition energies. The experimental values are compared with other measurements and with recent relativistic calculations along the lithium–isoelectronic sequence.

Solar EUV line identifications from delayed beam-foil spectra

A number of electric dipole transitions from low-lying long-lived levels in Si-, P- and S-like ions of Fe and neighbouring elements have been identified by their longevity in delayed EUV spectra after foil excitation of fast ion beams. Some of these new identifications pertain to previously unidentified lines in solar flare spectra.

Study of core excited quartet states in neutral sodium

Lifetimes and excitation behaviour of a number of core excited quartet levels in neutral Na, produced by beam foil excitation, have been established. The present results have helped to resolve the discrepancy seen in the published lifetime values of the 3s4s 4P5/2 and 3s3d 4P5/2 levels. Further, a new line having a wavelength of 4343 AA displaying similar excitation behaviour to the known transitions between the quartet states has been observed. Its lifetime is measured to be 0.91+or-0.13 ns. It is suggested that this line is most probably due to a transition between the 3s(1P)3p 2/2P3/2 and 3s2(1S) 2P3/2 states.

Beam-foil lifetime measurements on intercombination transitions in Kr I-like spectra of Nb, Mo, Ag and I

The relative intensities of the three Δn=0 ground state transitions 4p 6 1S 0-4p 5 4d 1P 1 0, 3P 1 0, and 3D 1 0 in Kr-like ions have shown peculiarities in spark spectra, and only two of these transitions (from 1P 1 0 and 3D 1 0) have been seen in tokamak spectra. We have recorded delayed spectra after foil excitation of fast ion beams of Nb, Mo, Ag and I ( Z=41-53) and obtained decay curves of the two longer-lived levels 4p 54d 3D 1 0, 3P 1 0. The experimental lifetime results agree with predictions. For the 3d 10–3d 94p resonance lines in the spectrum of Ni-like Br 7+, also involving the opening of a closed shell, measured and predicted lifetimes are also consistent with each other.

Variations of carbon foil lifetimes under bombardment by N+, Ne+, Ar+ and Zn+ ions

Studies of the useful lifetime of 2-5 µg cm−2 carbon stripper foils have been made using 225 keV heavy ion beam bombardment. The foils were self supporting and were mounted both in a standard and a tension-slackened manner. In determining the quality of the foil during ion bombardment several techniques were used, in particular beam-foil spectroscopy. Here the intensity of the light emitted by the foil-emergent beam was measured as a function of bombardment time. The measured lifetime before foil failure for standard foils was found to agree well with a semiempirical model proposed by Auble and Galbraith, and the slackened foils exhibited usable lifetimes 3-4 times longer than the normal foils. The properties of ordinary and slackened foils were compared under realistic conditions. It is concluded that the slackened foils are very well suited for studies of atomic spectra and meanlives of excited states using beam foil excitation methods.

Lifetime of the 4s4p 3P1o level in foil-excited Zn-like Mo12+ and Ag17+ ions

Spectra of 19 MeV Ag ions after foil excitation have been recorded at the foil and at various distances from the foil. The spectra show a multitude of long-lived decays. A decay curve of the only known long-lived transition, the intercombination line 4s2 1S0-4s4p 3P1o in Zn-like Ag17+, yields a lifetime of τ = (1.18 ± 0.08) ns which compares well with results from a MCRRPA calculation. A similar measurement on Mo12+ yields τ = (4.5 ± 0.3) ns.

Study of 3d ? 4f and 3d ? 5f quartet and doublet transitions of doubly excited three-electron ions

We present the first observation of optical transitions between doubly excited doublet states in the term systems N V, O VI and F VII. The spectra were produced by foil excitation of fast ion beams. The assignment of the spectral lines was made by comparison with the results of MCDF calculations along the isoelectronic sequence. The same method also led to the identification of two 3d – 4f quartet transitions in Mg X.

Formation of Rydberg states in fast ions penetrating thin carbon-foil and gas targets.

The absolute field-ionization yields of gas- and foil-excited Rydberg states are measured for different fast beam ions. From the yields a direct comparison of the quantum-state populations of high-n states (n>100) produced by gas and foil excitation could be obtained. Model calculations are consistent with the high-n states being predominantly produced by excitation of the projectile or capture of target electrons in the last layers of the solid target.

Spectroscopy of heavy few-electron ions

With the possibility to accelerate even very heavy ions to high velocities a new period has been opened in atomic structure investigations; Spectroscopic studies of heavy few-electron ions are feasible nowadays for instance for H- and He-like ions up to atomic numbers of about Z = 40 and for F- and Ne-like ions for practically all Z numbers (Z = 90), respectively. An overview on the available data and current experiments is given. The three different main experimental approaches are compared: the approach using the recoil ion light source, the beam foil excitation method and the acceleration stripping deceleration procedure in combination with a final electron capture. An outlook on further developments and future experiments is given.

Branching Ratios and Oscillator Strengths of Δn = 0 Transitions in the L-Shell of C I, N I, and O I Like Ions

Gas and foil excitation by and of ion beams from the 1 MV van de Graaff accelerator at Giessen and the 4 MV Dynamitron tandem accelerator at Bochum have been employed to induce Δn = 0 transitions in the L-shell of C I, N I and O I like ions of O, F, Ne and Si. Branching ratios have been measured and f-values have been determined using experimental lifetimes and the measured branching ratios. The results are compared with atomic structure calculations along isoelectronic series. Good overall agreement with the NCMET-formalism is found.

Satellite Lines in the EUV Spectrum of Foil-Excited Lithium

The EUV spectrum of lithium in the wavelength range 10-28 nm has been recorded with high spectral resolution. About one hundred lines of Li III, singly and doubly excited Li II and doubly excited Li I have been identified. The line-rich spectrum obtained after foil excitation is contrasted with the spectrum obtained after He gas excitation of Li+ ions. The lifetimes of three core-excited states have been determined and found to agree with theoretical predictions.

Beam-foil lifetime measurements for tellurium ions belonging to the Ag i and Cd i isoelectronic sequences

We have observed the spectrum produced by foil excitation of a beam of tellurium ions having an energy of 1 MeV. We have measured the lifetimes of the 5s5p1P1° and 3P1° levels, the 5s5d1D2 and 3D1,2,3 levels, and the 5p21D2 and 5s6s3S1 levels of Te v, and the 5p2P1/2,3/2°, 5d2D3/2,5/2, 6s2S1/2, and 6p2P1/2,3/2° levels of Te vi. The results are compared with a variety of calculations the agreement being quite good in most cases, particularly for the two resonance transitions at 895 A (Te v) and 951, 1071 A (Te vi), where our values were obtained using andc analyses. The variation of the f value with Z is discussed for the 5s2S–5p2P° transition along the Ag i isoelectronic sequence and for the 5s21S–5s5p1P° and 5s21S–5s5p3P° transitions along the Cd i isoelectronic sequence.

Doubly Excited States in B III

The core-excited quartet and doublet spectra of B III, produced by foil excitation of fast B+-ion beams, have been studied in the wavelength region 300-6300 Å. A large number of new transitions have been observed, for the first time allowing a detailed test ot theoretically predicted core-excited B III 4L- and 2L-term schemes. For a number of quartet states, the line assignments are supported by lifetime measurements. All the assigned, core-excited spectral lines are in excellent agreement with theoretical predictions by Chung et al. These predictions have been extended to include quartet states with L > 2.

Observation of quartet-state fine structures and lifetimes in lithiumlike Ne VIII

Wavelength and lifetime measurements for the fine-structure components of the $1s2s2p^{4}P^{o}\ensuremath{-}1s2{p}^{2}^{4}P$ multiplet in lithiumlike Ne VIII have been made using foil excitation of a fast-ion beam. The results are compared with recent theoretical calculations and with previous measurements for other ions of the same isoelectronic s\equence. An apparent discrepancy between theory and experiment for the $1s2{p}^{2}^{4}P_{\frac{3}{2}}$ lifetime is removed.