P. M. Griffin

Production of soft X-ray emitting slow multiply charged ions: Recoil ion spectroscopy

Abstract A study of Ne L-shell vacancy production by S ∼14+ , Cl ∼12+ ions has shown copious production of NeIINeVIII excited states with ∼10 −18 cm 2 cross sections and recoil velocities which may permit significantly higher resolution spectroscopy than is possible with beam-foil methods.

Observation of intense low energy autoionization lines in the wings of the forward peak from fast ion-atom collisions

In the ejected electron spectra from collisions of C2+, O4+ and Si10,11,12+ with argon toms at energies of 2–4 MeV/amu, a series of intense lines has been observed, which originates from doubly excited autoionizing states of Belike projectiles. These lines correspond to electron energies between 2 and 20 eV in the projectile frame. For kinematic reasons these lines can only be detected near the forward direction.

Radiative Lifetimes and Oscillator Strengths for Allowed Transitions in Li-like and Be-like Si

The lifefimes of the (2p)2P3/2 level in Si XII and the (2p2)3P2,1,0, (2s2p)1P1 and the (2p2)1D2 levels in Si XI have been determined using the beam-foil method. It is proposed that existing discrepancies between experimental and theoretical f values for the (2s2)1S0-(2s2p)1P1 transition in some ions of the Be sequence may be the result of the inability of the experimentalist to account for strong cascading from the (2p2)1S0 level.

Studies of neonL-shell excitation by impact of highly ionized heavy ions

Passage of foil-excited 1.4 MeV/A S and 1.1 MeV/A Cl ions of neon charge state ∼ 12+ through neon gas targets at pressure ∼100 mTorr has been found to be accompanied by copious production of Ne II–VIII excited states. Comparable excitation cross-sections ∼10−18 cm2 are found for a large number of levels belonging to all of these charge states and corresponding to principal quantum numbersn=2, 3, 4. Vacancy distributions very similar to those found in beam-foil excitation of ∼1MeV neon beams are found. Because the Ne recoil velocities are small compared to the fast beam velocities characteristic of the beam-foil source, it is possible to reduce both Doppler shifts and spreads by 3–4 order of magnitude for equivalent collimation. It has also been found that there is an excitation cross-section change of a factor ∼5 for a corresponding projectile charge state change from 6+ to 12+, that efforts to classifyK x-ray satellite spectra byLshell vacancy labels (KL0,KL1,...) are probably inaccurate due to extensive population ofn≧3 spectator levels, that both the recoil ion and beam-foil spectra exhibit few lines withn≧4, and that for the allowed transitions studied here, collisional excited states quenching effects due to the ∼100mTorr target gas pressures used are negligible.

Optically in accessible core excited states of Li and Na

Abstract The first observations of a number of optically inaccessible core-excited autoionizing states of lithium and sodium have been made. For example, the (1s2s 2 ) 2 S and (1s2p 2 ) 2 D states of Li have excitation energies of 56.31±0.03 and 61.04±0.03 eV, respectively.

Extreme ultraviolet spectra of highly stripped silicon ions

We report on a study of foil-excited spectra in the wavelength range 107–374 A from highly stripped Si ions. Decay-in-flight lifetime measurements involving the most prominent and well resolved features will be reported in a future publication. Many of the lines that have been identified are associated with Δn = 0 transitions in Si VI - Si XI of the type 2s22pk - 2s2pk+1 or 2s2pk - 2pk+1. A large number of the spectral features remain unidentified at the present time.

Electron spectroscopy of foil-excited chlorine beams☆

Abstract We report on a recent spectroscopic study of autoionization electrons emitted by fast, foil-excited chlorine ion beams. The observed electrons originated in the decay of certain core-excited metastable autoionizing states in lithium-like and sodium-like chlorine. Such states are metastable since they are forbidden to autoionize via the strong Coulomb interaction but decay instead via second-order magnetic interactions (or in some cases, radiatively). Chlorine beams from the Oak Ridge tandem accelerator were passed through thin carbon foils (≈ 15 μg/cm2) which served both to strip and excite the ions. Electrons emitted in the decay of autoionizing states thus formed were energy analyzed after the foil by a cylindrical mirror analyzer, the position of which could be varied with respect to the foil to facilitate time-of-flight lifetime studies. Beam energies were chosen to maximize the production of the lithium-like (Cl14+) and sodium-like (Cl6+) charge states. The results of a measurement of the energy and the lifetime of the (1s2s2p) 4 P 5 2 state of Cl14+ will be presented. A spectrum of autoionization electrons from Cl6+ will also be shown, but firm identification of many of the states of this system is at present difficult due to the almost complete lack of theoretical calculations of the energies and lifetimes of such states.

A survey of problems in beam-foil spectroscopy of iron and copper at energies from 16 to 110 MeV☆

Abstract Beam-foil spectra of iron and copper beams with energies between 16 and 110 MeV have been surveyed in the wavelength region from 20 to 350 nm. Transitions between Rydberg, as well as deeper-lying states, are identified. The results show that precision beam-foil spectroscopy on medium weight elements is difficult at high beam energies with typical heavy ion beam currents available from present accelerators and present photon analysis systems.

Anomalies in the beam-foil measurements for δn=o transitions in highly ionized members of the Li, Na, and Cu sequences

Systematic trends of absorption oscillator strengths for Δn=O transitions of the lithium, sodium, and coppper isoelectronic sequences have recently been established via agreement between theoretical calculations and benchmark beam-foil experiments. Although accurate mean lives have now been extracted from beam-foil decay curves, several anomalies have appeared. These are: 1) An unexpected sharp rise near foil zero in decay curves for the 2s 2S1/2 - 2p 2b1/2 transition in Li-like titanium, iron, and krypton. 2) Unexplained intensity modulations in decay curves for Na-like nickel, copper, and bromine. 3) Unpredicted satellite lines that may be associated with the Δn=O transitions in Cu-like iodine. Possible origins and explanations for these apparent anomalies are discussed.

Continuum electron capture dependence on projectileZ and velocity

Continuum electrons centered in velocity about that of the projectile and ejected near zero degrees in the laboratory frame have been observed for collisions of highly stripped Cq+ and Oq+ ions incident on Argon. For fully stripped projectile ions, the Z dependence and the velocity dependence of the continuum capture cross section have been determined for beam energies of 1.6 to 2.8 MeV/amu. Striking disagreements are noted between some results of this work and present theoretical predictions.