H. v. Buttlar

Beam-Foil Lifetime Studies of Highly Ionized Silicon

Previous beam-foil lifetime studies in the EUV range are extended to cover all n = 2 states of Si VII and Si IX. The lifetime values obtained agree with theoretical data of Nicolaides and Beck. For some states of Si X and Si XI information about initial population ratios of singly and doubly excited states is obtained. After foil excitation, the contribution of cascades from doubly excited states in the n = 2 shell to the intensities of decays from singly excited to ground states amounts to 20-40%.

Determination of beam-foil lifetimes <100 ps with a grazing-incidence spectrometer

Abstract Lifetime determinations of radiative atomic transitions in the extreme ultraviolet region with the beam-foil technique suffer from the fact that the spectrometer views a section of the beam that corresponds to several decay lengths. A method is presented which allows to measure lifetimes down to 10 ps by taking into account the window function of the spectrometer including the angular dependence of the grating reflectivity.

Lifetimes and initial populations of foil-excited hydrogen and lithium states

Abstract Ion beams of hydrogen and lithium are accelerated to energies of 50–400 keV and sent through a thin carbon foil. The decay of hydrogen states is observed by recording light intensities as a function of distance behind the foil. Two detectors are used simultaneously to measure Lyman-α and Balmer lines. They consist of an interference filter with cooled multiplier and an MgF 2 filter with channeltron, respectively. A correlated fit of both decay curves allows satisfactory elimination of cascade effects and yields an experimental lifetime for Ly-α of (1.592± ±0.025)ns. The main error results from uncertainties in the beam velocity. The initial state populations obtained using H 2 + and proton beams show significant differences which may be of interest concerning the ion-foil interaction problem. The lithium spectrum is measured between 400 and 1500 A using a 6 Li + beam viewed by a 0.5 m Seya-Namioka VUV monochromator with a channeltron detector. In this range, all known Li II transitions are found and most of them are investigated for lifetimes, cascades, and initial state populations. Also lines in the hydrogen-like Li III spectrum are observed, equivalent to H α through H σ . Their decay curves reveal the existence of a long-lived cascades which is believed to originate from an autoionizing state of Li + .

Correlation of energy loss and crystallographic transformation in ion-irradiated carbon foils

Abstract Fast ions in the energy range 100–400 keV traversing carbon foils of typically 5–15 μg / cm 2 surface density suffer a specific energy loss of 1–1.7 keV / μg cm −2 per ion. The energy deposited in the foil causes a continuous crystallographic transformation (graphitization) leading to an increase of the mass density and also of the energy loss per ion (at constant surface density). The rate of the energy loss variation is investigated as a function of the atomic nuumber of the projectile, the current density, and the projeċtile energy. It is shown that the increase of energy loss is a consequence of the crystallographic transformation and may be interpreted in terms of the Lindhard-Scharff theory.

Beam-Foil Lifetimes of Highly Ionized Silicon

Electronically excited states of Si ions are created by passing a 20 MeV Si5+ beam through a thin carbon foil. The EUV-radiation (λ=13–61 nm) emitted by the beam is analyzed using a grazing-incidence spectrometer. From the decay curves, lifetimes of 24 low lying levels in Si VIII to Si XII and of the 4f and 5g levels of Si XI and Si XII are derived. Cascades from doubly excited states turn out to be an important contribution to the radiation observed. The lifetime values of this work are compared to theoretical data mainly of Wiese, Sinanoλu and Dankwort/Trefftz. Most experimental values agree with at least one of the theoretical values. The decay time 560 ps of the 2s2p33D30 state of Si IX is clearly longer than the theoretical prediction (highest value 455 ps by Sinanoglu).

Beam-Foil Study of Titanium in the EUV Using Foils of Different Materials

The ultraviolet spectrum (λ8-60 nm) of highly ionized titanium after foil excitation of 15 and 20 MeV fast ions has been recorded. A number of new lines, mainly in sodiumlike Ti XII, are identified. Line intensity ratios and decay curves are measured in selected cases. Using foils of different materials, relative intensities of yrast transitions n = 3-6 are evaluated and intercompared with the aid of cascade models. Decay curves of yrast levels are studied for resonance effects in the population mechanism. Little evidence is found for such effects.

Ionenstrahlspektroskopie mit Wasserstoffionen als Primärteilchen

Relative initial populations of foil-excited hydrogen atoms in the2p, 3s, 3p, and3d states are determined by measuring the Balmer-α and Lyman-α emissions simultaneously. The data are analyzed by a computer program which takes into account the correlation of both emissions. The results show a dependence on the kind of incident ions: molecular ions give more light and lead to more pronounced excitation of higher angular momentum states than do atomic ions. A possible mechanism to explain this “molecule effect” is discussed qualitatively.

Messung von Lebensdauern und relativen Besetzungszahlen angeregter Zustände des Wasserstoffatoms mit der Methode der Ionenstrahlspektroskopie

H2+ ions or protons, accelerated to energies between 80 and 300 keV, are sent through a thin carbon target. Light emitted by the excited atoms moving out of the foil with a definite velocity is analyzed using interference filters and a cooled photomultiplier. Intensities of theHα,Hβ, andHγ lines are measured as functions of the distance from the foil. The data is analyzed with a computer program, which yields (in agreement with theory) mean lives of the hydrogen atom excited states involved, and the relative initial state populations of states belonging to the same principal quantum number. There is no indication of cascading.

Wavelength measurements in the quartet term system of doubly excited OVI and FVII

In the emission spectra of beam-foil excited oxygen and fluorine, it has been possible to assign lines to the quartet term systems of doubly excited three electron ions. A comparison with known spectra of singly excited four-electron systems turned out to be useful for line identification. The measured wavelengths are compared to theoretical predictions.

The Quartet Term System of Doubly Excited O VI

A total of 130 transitions in H-like, He-like, Li-like and Be-like oxygen have been observed in the wavelength region 7-32 nm using beam-foil excitation. A number of new lines are assigned to transitions in the doubly excited quartet system of O VI. The structure of this term system is derived from theoretical and experimental evidence. It is compared to the doubly excited term systems within the Li isoelectronic sequence.