Lyman X-ray Research Articles

Wavelength-dispersive spectroscopy in the hard x-ray regime of a heavy highly-charged ion: the 1s Lamb shift in hydrogen-like gold

Accurate spectroscopy of highly-charged high-Z ions in a storage ring is demonstrated to be feasible by the use of specially adapted crystal optics. The method has been applied for the measurement of the 1s Lamb shift in hydrogen-like gold (Au+78) in a storage ring through spectroscopy of the Lyman x-rays. This measurement represents the first result obtained for a high-Z element using high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime, paving the way for sensitivity to higher-order QED effects.

X-ray-emission measurements following charge exchange between C6+and H2

Lyman x-ray spectra following charge exchange between C$^{6+}$ and H$_2$ are presented for collision velocities between 400 and 2300 km/s (1--30 keV/amu). Spectra were measured by a microcalorimeter x-ray detector capable of fully resolving the C VI Lyman series emission lines though Lyman-$\delta$. The ratios of the measured emission lines are sensitive to the angular momentum $l$-states populated during charge exchange and are used to gauge the effectiveness of different $l$-distribution models in predicting Lyman emission due to charge exchange. At low velocities, we observe that both single electron capture and double capture autoionization contribute to Lyman emission and that a statistical $l$-distribution best describes the measured line ratios. At higher velocities single electron capture dominates with the $l$-distribution peaked at the maximum $l$.

X-ray emission from highly-charged ions after electron transfer in slow collisions: the role of multiple capture processes

We have studied 15 keV/q Ar17+ impact on atomic Ar experimentally and theoretically. Our analysis shows that multiple capture processes followed by autoionization contribute strongly to the measured Lyman X-ray emission intensities in the heliumlike projectile.

Effect of collective response on electron capture and excitation in collisions of highly charged ions with fullerenes.

Projectile deexcitation Lyman x-ray emission following electron capture and K excitation has been studied in collisions of bare and Li-like sulphur ions (of energy 110 MeV) with fullerenes (C(60)/C(70)) and different gaseous targets. The intensity ratios of different Lyman x-ray lines in collisions with fullerenes are found to be substantially lower than those for the gas targets, both for capture and excitation. This has been explained in terms of a model based on "solidlike" effect, namely, wakefield induced stark mixing of the excited states populated via electron capture or K excitation: a collective phenomenon of plasmon excitation in the fullerenes under the influence of heavy, highly charged ions.

Effect of collective response on the X-ray emission due to electron capture in high energy bare ion collisions with fullerenes

Electron capture by bare S ions was studied in collision with C60 and gas targets. The Lyman X-rays from the projectile were detected. It is observed that the intensity ratios of different Lyman X-ray lines in collisions with C60 are substantially lower than that for the gas targets. An attempt is made to explain this observation as a “solid-like” effect, namely, wake field induced stark mixing of the excited states populated via electron capture.

Measurement of the strong interaction parameters in antiprotonic hydrogen and probable evidence for an interference with inner bremsstrahlung

The spin-averaged values of the 1s strong interaction parameters in antiprotonic hydrogen were measured with good statistics. The results are: shift (ϵ 1s) = −712.5 ± 20.3 eV and width (Γ 1s) = 1054± 65 eV . These values are compatible and have approximately the same precision as the world average before this experiment. With some additional constraints, both the triplet and singlet components could be extracted from the same spectrum. The results are: 3S 1 shift: −785 ± 35 eV , 3S 1 width: 940 ± 80 eV , 1S 0 width: 1200 ± 250 eV . In addition, precise values for the Kα Lα and Ltotal Lα yields at low pressure (20 mbar) were obtained: 0.0176 ± 0.0016 and 1.45 ± 0.05. Furthermore, the 2p mean absorption width of 30.8 ± 3.0 meV was deduced, also compatible with and of similar precision as the world average before this experiment. An indication of interference between the measured Lyman (Ki) x-ray series and the process of inner bremsstrahlung due to charged meson production after annihilation was seen because of the low background conditions of this experiment.

X-ray studies on muon transfer reaction from excited states of muonic hydrogen atoms to deuterium atoms

The muon transfer reaction from excited states of muonic hydrogen atoms was studied directly by observing the characteristic Lyman X-rays of muonic hydrogen isotopes and the ground-state population of muonic hydrogen atoms, q 1s, was determined for low density H 2–D 2 mixtures. The time spectra of muonic X-rays and the ratio of K β to K α X-ray yields were also examined for detailed mechanism of the muon transfer reaction.

Muon transfer in excited states of muonic hydrogen probed by Lyman X-rays with an advanced Si(Li) detector

A study on the muon transfer reaction in the excited states of muonic hydrogen has been started at the pulsed muon facility of UT-MSL in the National Laboratory for High Energy Physics (KEK). Muonic X-rays from a mixture of protium and deuterium were detected and resolved successfully with a high-resolution Si(Li) X-ray detector,qls for a low-density p-d mixture was obtained with this elegant method.

Inclusive cross sections in collisions of multicharged ions with dressed targets

The formalism of inclusive probabilities allows the computation of many-electron cross sections from single-particle amplitudes in the framework of the independent particle model. We use this formalism to calculate projectile Lyman X-ray emission cross sections in collisions between Kr34+ ions and various dressed targets. We show that target electrons play a major role in the collision dynamics and that Lyman X-ray emission cannot be interpreted as arising from pure single excitation of projectile electrons. This brings new insight into the saturation of excitation cross sections and the validity of the one-electron model for the case of many-electron targets. Our results compare very well with recent experimental data.

New investigation of saturation effect in ion-atom excitation

Excitation cross sections of Kr34+ ions colliding with various target atoms, (Zt between 6 and 40) at nu =35 au have been investigated both experimentally and theoretically. The experimental cross sections were obtained from those for production of projectile He-like and H-like Lyman X-rays. The combined experimental and theoretical analysis of H-like emission allowed for a determination of the competitive capture-ionization process, whose contribution to the Lyman production cross sections is important for near-symmetric collision systems and has to be subtracted. A saturation effect of the experimental excitation cross sections with Zt is analysed from the theoretical point of view through atomic and molecular coupled-state calculations.

Contribution of intrashell excitation to the 1 mixing of excited states of one-electron ions in solids

Target thickness dependence measurements of Lyman X-ray emission cross sections in collisions of 33 MeV u-1 Kr36+ ions with C, Al and Cu targets have been performed. The results have been compared with the predictions of a rate-equation model including the nl-nl' process. The needed intrashell excitation cross sections have been calculated for 2<or=n<or=10 in the PWBA with screening and antiscreening effects accounted for. Using these cross sections, poor agreement with experiment is obtained. On the other hand, a set of fitted l-changing cross sections can be found to reproduce the data. These last cross sections are a factor 3-50 larger than the calculated ones. The authors believe this discrepancy to be an indication of a specific effect of free (or quasi-free) electrons in solid targets.

Measurement of balmer and lyman X-rays in antiprotonic hydrogen isotopes at pressures below 300 hPa

X-Rays of Balmer and Lyman transitions in antiprotonic hydrogen and of Balmer transitions in antiprotonic deuterium were observed at pressures below 300 hPa using Si(Li) semiconductor detectors. The measurement was performed at the LEAR-facility at a beam momentum of 202 MeV/c. In order to stop antiprotons in a low pressure gaseous target with high efficiency, a novel technique, the cyclotron trap has been used. Absolute yields were determined and compared with cascade calculations. A distinct difference in the cascade of antiprotonic hydrogen and deuterium is found. The parameters of strong interaction in antiprotonic hydrogen are determined to beɛ 1s=−(620±100) eV,Γ 1s=(1130±170) eV andΓ 2p=(32±10) meV.

Characteristics of single capture nl distributions and double capture probabilities in slow collisions of Al13+, Al12+ and Ne9+ ions with two-electron targets (He, H2)

Relative intensities of Lyman X-rays consecutive to one- or two-electron capture have been measured for collisions of 4 keV u-1 Al13+, Al12+, Ne9+ ions with He and H2 targets. A method is presented to extract separate information on single and double transfer processes. Preferential n states, proportion of p substrates and mean l values populated by single capture are measured, together with double capture probabilities. Comparison of experimental results with theoretical predictions for one-electron systems with near-crossing radii suggest that the location of these crossings may be more important than target internal structure to determine final l distributions. Finally, for the investigated systems with different ionic charges but near-crossing radii, double capture probabilities are found to be quite similar.

Asymmetry of Stark-broadened Lyman lines from laser-produced plasmas.

The asymmetries, as well as the widths, of spectral line profiles emitted by highly ionized high-Z elements in a dense, laser-produced hot plasma may be of use in determining the density of these plasmas. Three effects which introduce asymmetries into the line shape are the ion-quadrupole interaction, quadratic Stark effect, and fine-structure splitting. In this paper a method is proposed for including the ion-quadrupole interaction. This technique is then combined with procedures for including the quadratic Stark effect and fine-structure splitting to obtain asymmetric Lyman x-ray line profiles which include all three contributions.

Total charge transfer cross sections for 400 MeV bare Fe26+ions colliding with He, N2, Ne and Ar targets

The authors have measured total cross sections for electron transfer between 400 MeV bare Fe26+ ions and He, N2, Ne and Ar targets, corresponding to intermediate to high reduced velocities, 1<or= nu / nu i,f<or=10 ( nu is the incident projectile velocity and nu i,f are the initial and final orbital velocities of the captured electron). The data were determined from the intensities of the Lyman X-rays emitted by the Fe25+ after electron capture. A first Born (OBK) calculation is in clear disagreement with the values for all the targets. On the other hand, the continuum distorted-wave method, the strong-potential Born method and the impulse approximation, all including the influence of intermediate continuum states upon the capture process, are in much closer agreement with the experimental results.

Muonic Lyman x-ray intensities in pure elements

Muonic x-ray intensity ratios [$\frac{I(\mathrm{Ki})}{I(K\ensuremath{\alpha})}$] have been measured for 21 pure elements in the range $4\ensuremath{\le}Z\ensuremath{\le}48$. The cyclic variation of these ratios with $Z$ is clearly seen to follow the pattern of the periodic table of the elements over this range. The product of $\frac{I(K\ensuremath{\beta})}{I(K\ensuremath{\alpha})}$ and nearest-neighbor distance in the pure-element lattices varies approximately linearly with $Z$ within each period.

Measurement of muonic X-ray intensities and Coulomb capture ratios in chlorides

Muonic X-ray spectra of 32 chlorides have been measured with Ge detectors. Coulomb capture ratios and Lyman X-ray intensities were determined, and correlations to target data established. The experimental capture ratios agree well with the values from a recently proposed formula.

Lyman X-rays from a highly stripped nitrogen beam

The Lyman series has been observed for the hydrogen-like system of bare nitrogen (+7) plus an electron. The experimental resolution for these X-ray lines is about 2 eV.