P. H. Heckmann

Intercombination lines in delayed beam-foil spectra

The intrinsic time resolution of the beam-foil light source has been utilized in order to single out and to identify intercombination lines in the Mg i, Al i, and Si i isoelectronic sequences for ions with nuclear charge Z = 18–30 (Ar, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn). The method is described, and wavelength and lifetime data are presented. For the ions in the Al i and Si i sequences, the level positions of the high–spin term systems (lowest quartet and quintet levels, respectively) have been determined.

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.

A beam-foil study of the 3s3p3d 4F levels in the Al-like ions of Ti, Fe and Ni

The decays of the high angular momentum, high spin 4F0 states of the electron configuration 3s3p3d in aluminium-like ions (with three electrons outside a closed shell) have been identified in delayed spectra of foil excited Ti, Fe and Ni ion beams. The line identifications were aided by HXR, MCHF, and MCDF calculations and are corroborated by lifetime measurements which demonstrate the differential longevity of the fine structure levels. A search for the related case of 1s2p3d 4F0 level decays in Li-like ions of Si, P and S failed.

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 + .

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.

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.

Beam-Foil Lifetimes of Be-like Ions of Elements from Mg to S

Decay curves of n = 2, Δn = 0 transitions in the singlet term system of 4-electron ions of Mg, Al, Si, P and S have been recorded. To investigate the time pattern in case of blends, some additional decays in 5- and 6-electron sulphur have been measured. The results are compared to theoretical predictions.

Beam-foil lifetime study of Al-like titanium, iron and nickel

The lifetimes of the resonance levels in the Al-like ions Ti X, Fe XIV and Ni XVI have been obtained from beam-foil measurements using a variety of analytical techniques. The spectral analysis and identification of cascade transitions necessary for application of the ANDC procedure have been aided by recent observations of laser-produced plasmas. The lifetime values obtained from ANDC analyses for the 3s 3p2 doublet levels agree well with predictions based on semi-empirical Hartree-Fock calculations. However, the ANDC results for the 3s2 3d levels fall between the values obtained using multi-exponential curve-fitting and from the calculations.