M.W. Clark

Resonant-transfer-and-excitation for highly charged ions (16 ≤ z ≤ 23) in collisions with helium

Abstract Significant new evidence is presented for resonant-transfer-and-excitation (RTE) in ion-atom collisions. This process occurs when a target electron is captured simultaneously with the excitation of the projectile followed by deexcitation via photon emission. RTE, which is analogous to dielectronic recombination (DR), proceeds via the inverse of an Auger transition, and is expected to be resonant for projectile velocities corresponding to the energy of the ejected electron in the Auger process. RTE was investigated by measuring cross sections for projectile K X-ray emission coincident with single electron capture for 15–200 MeV 16 S 13+ , 100–360 MeV 20 Ca 16+,17+,18+ and 180–460 MeV 23 V 19+,20+,21+ ions colliding with helium. Strong resonant behavior, in agreement with theoretical calculations of RTE, was observed in the coincidence cross sections.

Predicted electron-correlation effects in U89+ collisions with light targets at GeV energies

Abstract Calculations predict that electron-correlation effects contribute significantly to total single-electron capture in collisions of U 89+ with H 2 and C at GeV energies.

Resonant transfer excitation in U89+ + C and U90+ + H2 collisions

Abstract Resonant transfer excitation (RTE), which occurs when electron transfer (capture) is accompanied by projectile excitation in a single-collision event, has been investigated for relativistic uranium projectiles colliding with carbon foils and molecular hydrogen. The RTE process is mediated by the electron-electron interaction, and is analogous to dielectronic recombination (DR). As such, the present results provide a test of relativistic DR theory and, for the H 2 target, show that RTE can contribute significantly to total single-electron capture in very high velocity collisions.

Proposed measurements of dielectronic recombination using the Indiana cooler facility

Abstract It is proposed to measure dielectronic recombination (DR) using the IUCF Cooler. This process, which involves the electron-electron interaction, takes place when electron capture is accompanied by simultaneous excitation of the interacting ion resulting in the formation of a doubly-excited intermediate state. The IUCF Cooler, with its high electron beam intensity and high electron-energy resolution, provides a unique opportunity for investigating this fundamental atomic collision process. Specifically, it is proposed to measure DR for collisions of He + ions with electrons in the Cooler at relative energies (in the rest frame of the ion) of about 30–40 eV. The DR cross sections obtained will be used to test theoretical calculations of this correlated two-electron process, which apart from their fundamental interest, have applications to astrophysical studies and to the development of nuclear fusion plasmas.

CLOSE ENCOUNTERS OF THE MULTIPLE-CAPTURE KIND - CA IONS IN AR

Abstract Collisions in which a fast highly charged ion passes within the orbit of inner-shell electrons of a target gas atom are selected by emission of an X-ray from the projectile or target. Measurement of the projectile charge state after the collision, in coincidence with the X-ray, allows measurement of the charge-transfer probability during these close collisions. When the projectile velocity is approximately the same as that of the target electrons, a large number of electrons can be transferred to the projectile in a single collision. Results for 47–160 MeV Ca 17+ + Ar show that the relative electron-capture probability in a close encounter decreases with increasing projectile velocity.

Transfer ionization in 0.5–1.5 MeV/u O5–8+ + He collisions

Transfer ionization (TI), in which electron capture is accompanied by loss of the other electron from the target, been measured for 0.5 to 1.5 MeV/u 0/sup q//sup +/ ions (q = 5-8+) colliding with helium. These new measurements, in conjunction with previous measurements at lower energies, are used to formulate a scaling rule to describe the projectile energy and charge state dependences of TI for collisions involving helium targets. 10 refs., 2 figs.

IONIZATION AND CHARGE-TRANSFER IN HIGH-ENERGY ION ATOM COLLISIONS

Abstract Electron capture and loss by fast highly charged ions in a gas target, and ionization of the target by passage of the fast projectile beam, are fundamental processes in atomic physics. These processes, along with excitation, can be experimentally studied separately (“singles”) or together (“coincidence”). This paper is a review of recent results on singles measurements for electron capture and loss and for target ionization, for velocities which are generally high relative to the active electron, including recent ionization measurements for a nearly relativistic projectile.

Enhancement of radiative Auger emission in lithium-like 23V20+ ions

Measurements have been made of projectile X-ray spectra coincident with single electron loss in collisions of 3.5-9.0 MeV amu-1 23Vq+(q=19, 20, 21) ions with He targets under single collision conditions. Nonmonoenergetic X-rays observed in the coincidence spectra for V20+ (lithium-like) projectiles are attributed to the radiative Auger effect (RAE). The intensity of RAE photons relative to the characteristic K X-ray yield is more than an order of magnitude larger than expected from theoretical calculations and from earlier measurements for atomic targets.

K- and l-shell resonant transfer and excitation in ion-atom collisions

Recent experimental studies of resonant transfer and excitation (RTE) in ion-atom collisions are reviewed. In the RTE process correlated electron capture and projectile excitation occur together in a single encounter with a target atom. Measurements of Ca/sup q+/ + H/sub 2/ (q = 10 to 19) from 100 to 370 MeV establish the projectile charge-state dependence of K-shell RTE and provide a detailed test of the theory. Structure due to RTE is observed in the energy dependence of the total electron-capture cross sections for this collision system. A comparison of the Ca/sup 17 +/ + H/sub 2/ data with previous results for Ca/sup 17 +/ + He demonstrates the effect of the target-electron momentum distribution on the RTE process. Studies of 230 to 610 MeV Nb/sup 31 +/ + H/sub 2/ provide information about RTE involving agreement with theoretical calculations. 15 refs., 4 figs.

L-SHELL RESONANT TRANSFER AND EXCITATION FOR NE-LIKE NIOBIUM IONS

Projectile excitation and charge transfer (capture) can occur simultaneously in a single encounter with a target atom through the electron-electron interaction between a projectile electron and a weakly bound target electron. This process is referred to as resonant transfer and excitation (RTE). L-shell RTE has been investigated for 230 to 610 MeV Nb/sup 31 +/ (neonlike) ions incident on H/sub 2/. 11 refs., 1 fig. (WRF)