T Azuma

Stabilized Hollow Atoms (Ions) Produced with Multiply Charged Ions Passed through Microcapillaries.

Ions of 9 keV/u Ne 9+ are impinged upon a microcapillary target along the capillary axis. X-rays emitted from the projectile downstream of the target show that a part of ions are in multiply excited states keeping a K-shell orbital open, i.e., hollow atoms (ions) are extracted in vacuum . Further, a considerable fraction of them are in extremely stabilized states with lifetimes of ∼ns which is more than 10 6 times longer than typical lifetimes of a Ne K-hole. A theoretical prediction suggests that core configurations with high spin multiplicities such as 1s2s2p 4 P are potential candidates of the stabilized fraction.

Potential sputtering of protons from a surface under slow highly charged ion bombardment

Sputtering phenomena have been experimentally studied for slow highly charged ions ( 0.5-4.8 keV Arq + ( q=4-16)). It is found that (1) the yield of proton sputtering from hydrogen-containing C60 strongly increases with the charge state of the incident ion, (2) the energy spectra of sputtered protons consist of two components which are identified as potential sputtering and conventional kinetic sputtering, and (3) the peak energy and width of the potential sputtering component depend very weakly on the incident energy and the incident charge, which is consistent with the prediction of the classical-over-the barrier model.

Angular distribution of X-ray emission from resonant coherently excited highly-charged heavy ions

Abstract X-rays emitted from resonant coherently excited (RCE) n =2 states of 390 MeV/amu hydrogen-like Ar 17+ ions were observed under planar channeling in a Si crystal. The resonance profiles for X-ray emission consisting of two peaks for j =1/2 and j =3/2 are characterized by suppression of the j =1/2 peak. The degeneracy of the n =2 states are removed by Stark effect due to the static crystal field. The RCE probability of these Stark splitted substates differs, reflecting the polarization of the oscillating crystal field. However, the associated alignment was not clearly observed. It is explained by the fact that both polarization of the oscillating crystal field and the wave functions of Stark-mixed n =2 states depend on the distance from the channel center, and the X-ray emission is preferred in a channel center in a crystal.

Positron Lifetime in C60/C70 Powder

Positron lifetime spectra have been measured in C 60 /C 70 and graphite powders at room temperature. It has been found that the spectrum for C 60 /C 70 has only one component of lifetime 393 ps, whereas that for graphite has three components of lifetimes 237 ps, 455 ps, and 88 ns. The single component in C 60 /C 70 does not originate from positronium. Considering its lifetime, the positrons ground state in C 60 /C 70 is supposed to be localized in the periodic free space of the C 60 /C 70 crystal structure.

Observation of a shape resonance of the positronium negative ion

When an electron binds to its anti-matter counterpart, the positron, it forms the exotic atom positronium (Ps). Ps can further bind to another electron to form the positronium negative ion, Ps− (e−e+e−). Since its constituents are solely point-like particles with the same mass, this system provides an excellent testing ground for the three-body problem in quantum mechanics. While theoretical works on its energy level and dynamics have been performed extensively, experimental investigations of its characteristics have been hampered by the weak ion yield and short annihilation lifetime. Here we report on the laser spectroscopy study of Ps−, using a source of efficiently produced ions, generated from the bombardment of slow positrons onto a Na-coated W surface. A strong shape resonance of 1Po symmetry has been observed near the Ps (n=2) formation threshold. The resonance energy and width measured are in good agreement with the result of three-body calculations.

Storage of negative carbon ions in an electrostatic ring

Negative carbon atomic ions and cluster ions were stored in an electrostatic ion storage ring. The lifetime of the metastable atomic ion is heavily affected by the blackbody radiation from the surrounding environment. By introducing rare gas target into the ring, collision-induced detachment cross sections of the atomic ion C- were obtained. For cluster ions Cn- (n = 2 ~ 8), decay of metastable ions with sub-millisecond to millisecond lifetime was commonly observed.

Doubly-resonant coherent excitation of HCI planar channeled in a Si crystal

We investigated resonant coherent excitation of H-like Ar17+ and He-like Ar16+ ions planar channeled in a Si crystal under the V-type and ladder-type double resonance conditions. In both cases, we observed distinct enhancement in the ionized fraction of the transmitted ions when the double resonance conditions were satis.ed. In the ladder-type configuration, the enhancement indicates that the doubly-excited 2p2 state of He-like Ar16+was produced through doubly-resonant coherent excitation.

State-selective scattering angular dependent fragmentation of N2 by slow Kr8+ ion impact

Abstract We have newly developed a multiple coincidence method to study state-selective scattering angular resolved fragmentation of molecules caused by slow highly charged ion impact. The fragmentation of N 2 in double charge changing collisions of Kr 8+ at 19 eV/u has been investigated using the multiple coincidence technique. The energy gain distributions and scattering angle distributions of product Kr 6+ ions in coincidence with the double time-of-flight of fragment ions are obtained for fragmentation processes of N + +N + ions, N + +N 2+ ions and N 2+ +N 2+ ions, and the reaction energies of their processes are determined.

Angular momentum distributions of Rydberg state electrons of Be-like sulfur produced through foil penetration

Spectra for Coster–Kronig (C–K) transition 1s 2 2pð 2 P3=2Þ9l ! 1s 2 2sð 2 S1=2Þel 0 of Be-like S 12þ ions produced following penetration of 2.5 MeV/u S qþ ions (q ¼ 7, 10, 12, 13) through C-foil targets of various thickness (1–6.9 lg/cm 2 ) have been probed using zero-degree electron spectroscopy. It has been found that in collisions for S qþ (q ¼ 7, 10) ion incidence, in which the C–K electrons originate from the projectile bound electrons, a fraction of the angular momentum l ¼ 1 of the Rydberg state decreases, and fractions of higher ðl P 2Þ angular momenta increase, while the total intensity of the C–K electrons grows, as target foil thickness increases. The electron spectra for S qþ (q ¼ 13) incident ions, in which the autoionizing Be-like state is preferably formed by electron capture from the target continuum upon or near the exiting surface, do not change in l-distribution or intensity. The shift to higher l comes from the multiple collisions of electron with the target, in traveling at the same speed under the strong Coulomb potential of the projectile. The observed dependence of the l-distribution and the intensity of the Rydberg state on projectile initial charge and target thickness indicates the importance of transport phenomena for both the S 13þ core and the projectile-entrained electrons inside solid. 2002 Elsevier Science B.V. All rights reserved.

Metastable states produced with beam–capillary interaction

Abstract The formation and relaxation processes of hollow atoms and related excited states of ions produced with a Ni microcapillary thin foil have been studied employing various experimental techniques. The first stage of the charge transfer from the surface to the ions was studied by using visible light measurements. On the other hand, X-ray measurements revealed the core electronic configurations of ions at the last moment of the hollow atom evolution. The overall feature of the electron capture processes in the capillary was given by the charge state distribution measurements.