R. S. Thoe

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.

Velocity dependence of the widths of electron-loss cusps in the range 7-12.5 au

The velocity dependence of the full width at half maximum of projectile electron-loss cusps is investigated. For Siq+, Oq+ and Cq+ projectiles traversing He, Ne and Ar targets in the velocity range 7-12.5 au, the FWHM is found to be independent of the ion velocity. These results disagree with theoretical predictions predating those of Day and restrict the velocity dependence of the anisotropy parameter beta in Days theory (1980).

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.

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.

Convoy Electrons from Solids in Coincidence with the Final Projectile Charge State

We measure the yield and final velocity distribution of electrons accompanying the projectile exiting from thin solid targets in coincidence with the projectile charge state. We find that the yield per emergent projectile and the longitudinal velocity distribution is independent of the final projectile charge state.