J. P. Forester

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.

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.

Polarization measurements of the non-characteristic radiation emitted from collisions between high energy A1 ions

Abstract We have measured the angular distribution of the non-characteristic K X-ray radiation (NCR) in very fast A1-A1 collisions and find that it agrees well with the maximum value predicted by the induced mechanism of Muller et al.

Dipole oscillator strengths for Δ n = 0 transitions in highly ionized sulfur☆

Abstract The foil-excitation method has been used to measure f-values for intra L-shell transitions in highly ionized sulfur.

Autoionizing states in highly ionized oxygen, fluorine and silicon

Excitation processes in atoms or ions usually involve the promotion of one of the least tightly bound outer shell electrons to a higher orbital leading to a state lying below the ionization threshold. It is possible however to form highly excited discrete states that are embedded in the continuum if one or more inner core electrons are raised to outer shells. In the present paper we report on such states in high Z 3-electron ions associated with core excited configurations of the type 1s2snl and 1s2pnl. Such states may autoionize rapidly via the Coulomb interaction unless forbidden to do so by selection rules on this process. These metastable autoionizing states either decay by radiation or autoionize at a slower rate via the weaker magnetic interactions. The lowest lying quartet state in 3-electron ions (1s2s2p)4P 5/2 o is metastable against both autoionization and radiation. Our previously measured lifetimes [1] for this state (in nanoseconds) are: S (1.1), Si (2.1), Ar (0.66), Cl (0.91), F (15), and 0 (25). Radiative decay processes involving core-excited states have also been previously observed. For example, one type of decay is an El transition between two metastable quartet states and another is a similar transition from a core excited state to a singly excited state.