A. E. Livingston

Beam-foil spectroscopy in the extreme UV of highly ionized silicon Si XI and the isoelectronic ions AI X, S XIII and Ar XV

Spectra of highly-ionized silicon, aluminium, sulfur and argon ions produced by the beam-foil technique have been analysed in the 5-40 nm wavelength range. Numerous transitions belonging to n = 3-4, 4-5 and 3-5 transitions arrays in the beryllium-like spectra Al X, Si XI, S XIII and Ar XV were observed for the first time. The assignment of spectral lines was corroborated by comparison along the isoelectronic sequence.

Measurement of the 6p2P3/2 state lifetime in atomic cesium.

We present a precision experimental test of atomic many-body theory that is currently applied to the interpretation of recent parity-nonconservation experiments in atomic cesium. We report the first measurement of the {sup 133}Cs 6{ital p} {sup 2}{ital P}{sub 3/2} state lifetime using resonant diode-laser excitation of a fast atomic beam. The lifetime result of 30.55{plus minus}0.27 ns determines the absorption oscillator strength for the 6{ital s} {sup 2}{ital S}{sub 1/2}--6{ital p} {sup 2}{ital P}{sub 3/2} transition in cesium to be 0.7133{plus minus}0.0064, and establishes the accuracy of recent relativistic many-body calculations of the dipole transition matrix element to 0.5%.

2s2 1S0 – 2s2p 3P1 Intercombination Transition Wavelengths in Be-like Ag43+, Sn46+, and Xe50+ Ions

Be-like Ag43+, Sn46+, and Xe50+ ions were produced by beam-foil excitation at the UNILAC accelerator of the GSI. The wavelengths of the 2s2 1S0–2s2p 3P1 intercombination lines were measured using the GSI 5 m grazing incidence spectrometer. The projectile spectra were calibrated in situ with well known ionic lines of a VUV Penning discharge lamp. A precise determination of the Doppler shift was necessary. An experimental precision of 10-4 was realized. Our medium-Z experimental results represent the heaviest Be-like ions studied. They are compared with published MCDF and MBPT calculations along the isoelectronic Be-like series. Excellent agreement exists between our Xe-value and a recent result from an electron beam ion trap.

Precision lifetime measurements using laser excitation of a fast atomic beam

Abstract We employ resonant laser excitation of a fast atomic beam to measure excited state lifetimes by observing the decay-in-flight of the emitted fluorescence. Our program includes lifetime measurements of the low lying p states in alkali and alkali-like systems. This work was initiated by the motivation to test the atomic many-body-perturbation theory that is necessary for interpretation of parity nonconservation experiments in cesium. We report new measurements of the 6p 2 P 1 2 and 6p 2 P 3 2 state lifetimes in the 133Cs atom to be 34.934 ± 0.094 ns and 30.499 ± 0.070 ns respectively. With minor changes to the apparatus, we have extended our measurement capabilities to include the 2p 2 P 1 2 , 3 2 states of lithium. We present comparisons between measurements and relativistic calculations of atomic transition matrix elements.

Wavelength and lifetime measurements on forbidden and intercombination lines in the EUV spectra of swift foil-excited highly charged ions

Intercombination transitions imply a change of spin which is not allowed in pure LS coupling. Forbidden transitions connect levels for which electric dipole transitions are not possible because of the parity selection rule. Both transition types are of much lower probability than allowed E1 transitions. They have been studied by time-resolved spectroscopy of foil-excited fast ion beams. The method is outlined in brief, and data are presented for highly charged ions of Ag and Xe.

Measurements of 2s–2p transition energies in helium-like and lithium-like nickel☆

The wavelength of the fine structure transition 1s2s /sup 3/S/sub 1/ - 1s2p /sup 3/P/sub 2/ in Ni XXVII has been measured using fast-ion spectroscopy. The transition energy is sensitive to relativistic and Lamb shift corrections in this high-Z two-electron system. Comparison is made with measurements in other high-Z ions and with recent theoretical calculations. A preliminary measurement of the 1s/sup 2/2s /sup 2/S/sub 1/2/ - 1s/sup 2/2p /sup 2/P/sub 1/2/ find structure transition in Ni XXVI is also reported. 18 refs., 1 fig., 2 tabs.

Structure of hydrogenic transitions in high-Z beryllium-like ions☆

Abstract The structure of hydrogenic states, or low lying Rydberg states, in highly-ionized beryllium-like atoms is influenced by the effects of atomic core polarization as well as configuration interaction. Measurements have been made, using fast-ion spectroscopy, of the resolved structure of hydrogenic transitions in S XIII and Cl XIV involving 1s 2 2s nl and 1s 2 2p nl states with n = 6–11. Relativistic MCHF calculations are compared with the observed structures.

Fine structure of the 2 3P state in helium‐like sulfur and chlorine

We present precision measurements of the 1s2p (3P2 ‐ 3P0) fine structure energies in the helium‐like ions S14+ and Cl15+. The fine structures are obtained from spectroscopic measurements of the 1s2s 3S1 ‐ 1s2p 3P0,2 transition wavelengths. These results represent the most precise experimental determinations of the helium‐like J=2 ‐ 0 intervals for Z≳5. They establish the magnitude of missing higher order relativistic contributions in previous high‐Z calculations of this fine structure, and they are in excellent agreement with new relativistic many‐body calculations.

Lifetime of the 22S1/2 state in hydrogenlike krypton

We report a measurement of the lifetime of 22S1/2 level in hydrogenlike 84Kr and the first determination of the branching ratio for the M1 decay for this Z=36 one‐electron ion. The lifetime of this state was measured by the beam‐foil time‐of‐flight method, in which the foil was moved relative to a fixed, collimated Si(Li) detector. An analysis based on the single photon spectra from a tightly collimated detector led to the measurements of the lifetime of 22S1/2, the two‐photon emission rate, the M1 emission rate and the branching ratio of M1 decay. All these exprimental results are in good agreement with the theoretical calculations of Parpia and Johnson, and Goldman and Drake.

Rydberg transitions in Be‐like Si XI

Measurements of Δn=1 Rydberg transition wavelengths for Be‐like Si XI are presented for 1s22s9l’←1s22s10l and 1s22s8l’←1s22s9l. The large polarizability of the open core 1s22s and configuration interaction with nearby 1s22pnl states yield observable 1‐structure that is compared with the polarization model, Multi Configurational Dirac‐Fock (MCDF) and Many Body Perturbation Theory (MBPT) calculations. We discussed the high‐1 structure of the n=9–10 transition previously in relation to plasma observations. The first application of MBPT calculations to Be‐like Rydberg states was reported with our measurement of the 7I–8K transition in S XIII.