J. Doerfert

Recombination measurements at low energies with Au49+,50+,51+ at the TSR

Recombination of Au49+, Au50+, and Au51+ ions has been studied at the TSR. With Au50+ ions a storage lifetime of only 2 to 4 s was observed with the magnetically expanded electron beam of the cooler at a density of ne = 107 cm-3. This short storage time is a consequence of the highest recombination rate coefficient ever observed with an atomic ion (1.8·10-6 cm3 s-1 at zero relative energy Erel = 0 between electrons and ions). At about 30 meV a huge dielectronic recombination resonance is found with a record small width of only about 15 meV. Such resonances fortuitously occurring near Erel=0 are probably the main reason for the enhanced recombination rates observed with Au50+, with Pb53+ (in a recent experiment at LEAR) as well as with other complex ions. For Au49+ and Au51+ the recombination rates are smaller by an order of magnitude.

Experimental n=3 level lifetimes of Na-like heavy ions in the realm of massive relativistic effects

Abstract The lifetimes of the 3p 2 P° resonance levels and of the 3d 2 D levels in Na-like ions Xe 43+ ( Z = 54) and Au 68+ ( Z = 79) have been measured by time-resolved spectroscopy of foil-excited ion beams. This represents a major step beyond the previous data which reached only up to Z =29, into the range with massive relativistic effects. The results corroborate the lifetimes predicted by very recent calculations of the atomic structure which also reproduce the experimental transition wavelengths.

Time resolved EUV spectroscopy on foil-excited 5.9 MeV/u Xe and 13.2 MeV/u Au ions

N=3, Δn=0 transitions in Na-like ions have been observed and the resonance level lifetimes have been measured by time-resolved spectroscopy of foil-excited ion beams of Xe (Z=54) and Au (Z=79). Other lines in the same wavelength range are identified withn=3, Δn=0 transitions in Ne-, Mg-, and Al-like ions. Wavelengths and transition rates for these new lines are compared to the available theoretical data. A number of experimental problems are discussed.

Beam-foil measurements on intercombination transitions in Cl-like ions of elements Mn through Zn

Prompt and delayed beam-foil spectra have been recorded in the wavelength range of the 3s23p5-3s23p4 3d transitions in Cl-like ions of the elements Mn through Zn. A comparison with simulated spectra reveals the presence of foreign intercombination lines, of ions in neighbouring charge states. For Fe, Ni and Cu a number of decay curves have been recorded at the wavelengths of prominent features in the delayed spectra. The results are compared with available theortical data. A number of solar lines can now be identified with intercombination lines in Cl I-like spectra of Fe and Ni.

Lifetimes of n = 2 levels in foil-excited Kr32+ and Kr33+ ions

Abstract N = 2, Δn = 0 transitions in highly-charged Kr ions have been observed with foil excited ion beams. Decay curves were constructed from delayed multi-channel spectra. Analysis of the decay curves by various techniques which take cascade effects into account yielded n = 2 level lifetimes in the range 10–50 ps. The lifetime results are compared with theoretical predictions for Kr as well as with the isoelectronic trend in the Li and Be isoelectronic sequences.

Extended analysis of intensity anomalies in the Al I isoelectronic sequence

This paper reports an extended experimental investigation, using the beamfoil technique, of the intensity ratio of the fine-structure components in the 3s23p 2P1/2,3/2–3s3p2 2S1/2 and 2P1/2 resonance transitions along the Al I isoelectronic sequence. These intensity ratios are strongly influenced by cancellation/enhancement effects arising from spin-orbit induced level mixings, and are thus sensitive probes of the detailed atomic structure. New data are given for Si II, P III, S IV, K VII, Sc IX, Fe XIV and Ni XVI. Together with previous experimental results this comprehensive isoelectronic study reveals significant and systematic deviations from theoretical predictions.

Measurements of long atomic lifetimes at an ion storage ring

Millisecond lifetimes of excited levels in multicharged ions may be measured at ion storage rings. At the Heidelberg ion storage ring TSR, particle detection after collisions between the circulating ions and electrons of the cooler has been used to obtain dielectronic recombination spectra as well as time curves of ionization and recombination for four-electron ions, with the aim of measuring transition probabilities for magnetic dipole and for electric dipole intercombination decays. The measurements on the 2s2p3P1o level in the Be-like ions of N and O indicate lifetime values of Τ=(1.6±0.2) ms for N3+ and of Τ=(0.5±0.1) ms for O4+. Problems of these experiments are discussed as well as the prospects for improved measurements on other such ions of astrophysical interest, planning for state-specific optical detection.

Search for the spectrally narrow radiative decay of 2p3 4So3/2 in He-

Radiative autoionization (RA) of the 2p3 4So state in the He- ion has been predicted to result in a narrow spectral feature near lambda =32.315 nm. The authors have observed a weak, line-like structure at lambda =(32.32+or-0.02) nm, in spectra of foil-excited He ions at incident energies in the range 140-200 keV. This would be the first observation of this elusive RA process. The measurements and supportive evidence are presented as well as preliminary results for electronically similar ions of B and C, in which the decay is taking place connecting bound states, as in the well studied cases of Li and Be.

Recent dielectronic recombination experiments

New recombination experiments with merged cold beams of electrons and atomic ions have been carried out at the storage ring facilities TSR in Heidelberg, ESR in Darmstadt, and CRYRING in Stockholm. A brief overview is given on the recent activities in which the Giessen group was engaged. Topics of this research were dielectronic recombination (DR) of astrophysically relevant ions, recombination of highly charged ions with respect to cooling losses in storage rings, field effects on DR, search for interference effects in photorecombination of ions, correlation effects in DR of low-Z ions, spectroscopy of high-Z ions by DR, and lifetimes of metastable states deduced from DR experiments.

Beam - foil study of the lifetimes of levels in Na-like Ca X, Mg-like Ca IX and Si-like Ca VII

Levels of Ca ions with one, two or four electrons in the n = 3 shell have been studied for their decay properties and lifetimes. For the levels of Ca X and the level of Ca IX, arbitrarily normalized decay curve (ANDC) and cascade model analyses yield results with precisions of 10% and less and with low systematic uncertainties. The measured lifetime of the Ca IX level confirms the need to include relativistic effects in the calculation. The lifetime results are compared to other, experimental and theoretical, data available for the isoelectronic sequences.