Steep dependence of recoil-ion energy on coincident projectile and target ionization in swift ion-atom collisions

Abstract

The first measurements of the mean energies E"ofhighly charged recoil ions detected in coincidence with multiply ionized swift projectiles are reported. Beams of 23-, 27.6-, and 33-MeV Cl'+ produced Ar recoil ions whose mean energies exhibited a strong dependence on the product (qr) of final projectile and recoil charge states. For large qr values, F" is substantially larger than earlier estimates, and allows inference of characteristic impact parameters without requiring measurements of projectile scattering angle.In the past decade, the production of low-energy highcharge-state recoil ions by swift, heavy-ion impact has been effectively exploited. Low-emittance recoil-ion sources have been used to provide spectroscopic sources of low Doppler spread, as well as to produce secondary beams for slow ion-atom collision experiments. ' The "ion-hammer" technique has proven a rich source of novel data on ion-atom collision phenomena, particularly on single-and multiple-electron capture in the 0.1-to-few keV per charge energy range. ' The possibility of producing a powerful, parasitic source of bare and few-electron lowenergy ions (greater than 10' extracted ions/sec), "hammered" at MHz frequencies in a heavy-ion storage ring, has been conjectured by Ullrich et al. Despite the abundance of activity in the field and the importance of the parasitic-ion-source possibility, few data concerning the energies and angular distributions of the primary recoil ions have been published.Ullrich et al.have recently published a measurement of the entire recoil-energy distribution for Ne + ions produced by 1.4-Mev/u U projectiles, using a specially designed time-offlight (TOF) spectrometer. Substantial new knowledge of intrinsic interest, as well as practical significance for design of parasitic sources, can be gained from measurements of recoil energies and angular distributions. This paper concerns the first quantitative measurements of the mean energies E, of slow, highly charged recoil ions produced in MeV/u collisions as a function of recoil-ion charge state r and emergent projectile charge state q. For high (q, r) values, E" is found to be several times larger than suggested by earlier estimates (made for more restrictive assumptions than apply here. ' The steep dependence of E"on q and r observed permits inference of a characteristic impact parameter b corresponding to the mean recoil energy for each (q, r) pair.This method thus augments difficult measurements of projectile scattering angle in coincidence with one or more reaction fragments, a method primarily useful for harder collisions and often requiring angular resolution of -100 prad. Since calculated target ionization transition probabilities are not sharply peaked in b, but typically extend over a range comparable to b, one expects the recoil ions to be spread over a corresponding range in E"and recoil angle. Present measurements are of mean recoil energies and thus indicate b, but not its range.The measurements were performed using a TOF method' already demonstrated (i...

High-Resolution Momentum Imaging—From Stern’s Molecular Beam Method to the COLTRIMS Reaction Microscope

“…11 These experiments were the first where-in high-energy heavy-ion rare-gas collisions ionization-probabilities at very small scattering angles <10 μrad were successfully measured. In parallel, the group of Ivan Sellin at Oak Ridge [45][46][47] measured mean energies of low energy recoil ions, too Fig. 12 Recoil-ion spectrometer of Dörner et al [44] (see text) Fig.…”

Measurement of the mean transverse kinetic energy of recoil ions produced in energetic electron atom collisions

“…Investigations on the mean transverse kinetic energies (MTKE) and the angular distributions of the recoils using the time of flight (TOF) technique have been made by several workers [1,[4][5][6]. The first direct electrostatic measurements of recoil energies did not appear until the measurements of Ullrich et al [7][8][9] and of Levin et al [10]. Cold target recoil ion momentum spectroscopy (COLTRIMS) has allowed for measurements of the transverse and longitudinal components of momentum of the recoiling target emerging from the ionizing collisions between an energetic projectile and target atom.…”

Multiple ionization of heavy targets by H+and hydrogen impact

“…Multiple ionization and capture has been largely investigated using highly charged projectiles, because they produce a wide range of recoil-ion charge states (Ullrich et al 1997, Hagmann et al 1986, Levin et al 1987, Schmidt Böcking et al 1991. Heavy projectiles at low (Bordenave-Montesquieu et al 1994) and intermediate (Ullrich et al 1989) impact velocities have been used to produce high recoil-ion charge states, in cases obtaining hydrogen-like heavy targets.…”