We report cross sections for ionization of He coincident with electron loss from He, Li, C, O, and Ne projectiles. For He, Li, C, and O projectiles, the cross sections were measured directly, while the Ne cross sections were obtained by transforming results for He projectiles colliding with Ne. We find that, at energies of about 100-500 keV/u, neutral projectiles can ionize a He target almost as effectively as a charged projectile. The contribution to ionization due to electron-electron interactions is found to scale with the number of available projectile electrons. Comparing ionization by the bound electrons on projectiles to ionization by free electrons, we find that the cross sections for ionization by bound electrons are systematically smaller than those for free electrons.

We report the investigation into the three-body fragmentation of the triatomic molecules NH2 and CH2 via the process of dissociative recombination (DR). Recently reported analysis of experiments into the DR of the similar system H2O indicated that the DR process is violent, involving a large degree of geometrical change and energy distribution from the initial attachment of the free electron by the parent ion to the final dissociation step. Comparison of data from NH2 and CH2 with that of H2O gives a similar picture of the DR process, though there are significant differences in the results, not only in the branching fraction between the expected decay channels, but also in the distribution of the available reaction energy over the product hydrogen atoms as well as in the molecular geometry at the point of dissociation.

Experimental data and theoretical results on charge loss -27less than or equal toDeltaZless than or equal to-1, charge pickup DeltaZ= +1, and total charge-changing cross sections for 158A (GeV82Pb)-Pb-208 ions on CH2, C, Al, Cu, Sn, and Au targets are presented. Calculations based on the revisited abrasion-ablation model for hadronic interaction and the relativistic electromagnetic dissociation (RELDIS) model for electromagnetic interaction describe the data. The decay of excited nuclear systems created in both types of interaction is described by the statistical multifragmentation model (SMM), which includes evaporation, fission, and multifragmentation channels. We show that at very high projectile energy the excitation energy of residual nuclei may be described on average as similar to40 MeV per removed nucleon, with some increase in this value compared to fragmentation of intermediate energy heavy ions at similar to1A GeV. The importance of the electromagnetic interaction in production of Hg-80, Tl-81, and Bi-83 projectile fragments on heavy targets is shown. A strong increase of nuclear-charge pickup cross sections, forming Bi-83, is observed in comparison to similar measurements at 10.6A GeV. This process is attributed to the electromagnetic production of a negative pion by an equivalent photon, which is quantitatively described by the RELDIS model.

X-rays emitted from resonant coherently excited (RCE) n=2 states of 390 MeV/amu hydrogen-like Ar17+ 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.

Much recent work in the field of dissociative recombination (DR) has been related to the break-up of polyatomic ions since, in spite of the apparent simplicity of DR, developing a general theory to predict product branching ratios for even the simplest polyatomic ions, e.g. X H 2 + , has proven to be difficult. Early models suggested that such ions would predominantly fragment to H + XH. However, all recent storage ring studies for such ions show a propensity for three body breakup, i.e. X + H + H.1−4 In the last year, the dynamics of some of these systems have been investigated, with results reported for H2O+ 5 and H 3 + ,6 and a brief review was also published.7 Using trajectory calculations, we have also investigated the dynamics on some of the potential surfaces involved in the DR of H2O+.8 The group at TSR looked at the dynamics in, and competition between, the two and three body fragmentation dynamics of H 3 + . Using a statistical model,9 they reached good agreement with the experimental data previously obtainedat CRYRING1 as a function of reaction energy.

We report on measurements of absolute scattered projectile charge fractions for Ar11+ ions with incident energies in the range 3–30 keV, that have been 120° back-scattered from CsI(100) in quasi-binary collisions. Use of a time-of-flight technique that incorporates a biased drift region permitted full separation of all scattered charged states, including neutrals. In contrast to our Ar11+ results for Au(110), the scattered neutral fraction is smaller, and relatively independent of incident projectile energy over the entire investigated range. In addition, we have measured, at a fixed energy of ∼5 keV, scattered charged state distributions as function of incident charge states in the range 1+ to 13+. In a separate measurement utilizing electrostatic instead of TOF analysis of the scattered charge states, we attempted to evaluate the effect of surface charging on energy loss of low energy scattered projectiles by absolute measurements of the scattered 1+ energies of incident Ar11+ ions incident on CsI(100) at energies down to 10 eV/q. Apart from small deviations from the elastic binary collision energy loss expected for large angle scattering, ascribable to the image charge interaction, no measurable effect due to surface charging was found down to the lowest investigated energies.

A strong increase of inclusive nuclear-charge pickup cross sections, forming 83Bi from 158A GeV 82Pb ions, is observed in comparison to similar measurements at 10.6A GeV. From the dependence of these cross sections on target atomic number, this increase is attributed to the electromagnetic process of pion production by equivalent photons. The observed cross sections can be reproduced quantitatively using the recently developed RELDIS code.

A reflecting ion beam electrostatic trap has been constructed and tested for the purpose of studying molecular ion physics. A trap of this type offers a large field-free region, wide mass range, and beam directionality that simplifies the detection of stored ions or breakup products. In our configuration, pulsed ions extracted Pram an ion source (5-10 mus) ate accelerated to keV energies and magnetically analyzed before injection into the trap. After the ions enter the trap, high-voltage electrostatic entrance and exit mirrors and Einzel lenses (operated by fast switches) cause the ions to oscillate between the mirrors in nearly parallel trajectories. Neutralized ions, detected by a channel plate located beyond the exit mirror, indicate the time dependence of the stored ion population. Voltages and pulsed timing of the beam and trap are controlled by computer (38 parameters). The computer can quickly find the optimum trapping conditions in successive fills using the detected neutral yield. Numerous atomic and molecular ions (energy of 1.3-3.0 keV and m < 100 amu) have been stored with a beam capture efficiency up to 2%. The storage lifetime, limited by neutralizing collisions with background gas, is typically 2-5 sec at a pressure of 2 x 10(-9) Torr.

Measurements of the energy loss and the energy-loss distributions of 160 GeV/amu fully stripped lead ions traversing a silicon single crystal are presented. The energy loss is measured using the silicon crystal as an intrinsic detector. Hence the measured energy loss is a restricted energy loss excluding very large energy transfers. For random incidence, the observed energy-loss distributions are very narrow and Gaussian-like. For well-channeled particles, the energy loss is strongly reduced as compared to so-called random particles. The observed energy loss is compared to calculations as well as simulations. Due to the small straggling, the energy-loss distributions are reflecting directly the distribution in transverse energy.

An electron, recombining with a molecular ion, deposits the negative of the ionization potential into the system and leads to dissociation into atomic and/or molecular fragments (dissociative recombination (DR)). Recent studies using heavy-ion storage rings have done much to elucidate the process. Relative collision energies as low as similar to1 meV are obtained, and information has been gained on total cross sections (rates), fragment branching fractions, and atomic states in DR of diatomic molecules. Tri-atomic di-hydrides (H-3(+), CH2+, NH2+, OH2+) show a propensity for dissociation into three fragments. To study the dynamics of this process, a new method has been used to obtain atomic excitation levels, distribution of energy, and angular distribution of the fragments. The case study of H2O+ has been completed and is discussed.

We report on the first experiment that measures simultaneously the full momentum vector of recoil ions and projectile energy loss and scattering angle in ion-atom collisions. We studied multiple ionization in the collisions of 0.83-MeV/u O7+ with Ne. Recoil ions ( Ne(q+), q = 1-8) were detected in coincidence with single capture to O6+. The results give the first experimental evidence for the increase of the average electron energy with increasing recoil charge state q. The average ejection angle shows a dramatic decrease with q. Results are compared with n-electron classical trajectory Monte Carlo calculations.

Cross sections for radiative electron capture (REC) by 33-TeV Pb82+ ions in Be and C targets have been extracted from an analysis of measurements of total electron capture by these ions in Be, C, Al, Cu, Sn, and Au targets. The REC cross sections in the Be and C targets, when REC is significant, were obtained by subtracting cross sections for electron capture from pair production (ECPP), the only other significant capture process at these energies. The ECPP contributions in Be and C were determined from extrapolations of measured cross sections in the heavier targets where the ECPP process dominates, with suitable accounting for slightly decreased screening effects for the light targets. We obtain an experimental K-REC cross section (0.010 +/- 0.002b per electron per Pb K vacancy), which agrees with a calculation of REC made by applying detailed balance to the corresponding process of radiative recombination and using tabulated photoelectric effect cross sections. A comparison is also presented of the present experimental result with other heavy-ion measurements made at lower energies, and with nonrelativistic and relativistic calculations, which differ considerably in this energy regime.

At ultrarelativistic energies, we encounter unusual phenomena which control electron capture and loss and which contribute to the stopping power of ions. Electron capture becomes dominated by capture from electron–positron pairs, projectile-ionization cross-sections saturate as the “maximum” impact parameter exceeds the Thomas–Fermi radius of a neutral target atom and the stopping power is reduced when the wavelength of the target electron with respect to the moving ion approaches nuclear size.

Electrons ejected in the forward direction from fully-stripped and one-electron 33-TeV Ph ions passing through thin foils of Al and Au have been studied. Spectral peaks centered at a momentum equivalent to the velocity of the projectile have been measured, which are attributed toelectron loss to the projectile continuum(ELC). From previous theoretical studies, the ELC 'cusp' shape is expected to reflect the initial state of the electron released from the projectile. The ELC peaks are very narrow even for loss from ground-state incident ions. The observed widths arise primarily from instrumental broadening effects - especially multiple Coulomb scattering (MCS). Correction of the measured electron momentum distributions for instrumental broadening leads to very narrow ELC cusps, which have essentially the same widths for loss from incident one-electron ground-state ions and loss from hydrogenic ions populated by electron capture from pair production (ECPP), where there should be significant excited-state formation.

To better understand the propensity for the three-body breakup in dissociative recombination (DR) of dihydrides ( H(3)(+), NH(2)(+), CH(2)(+), and H(2)O(+)), we undertook a study of the dynamics of this process. A study of DR of H(2)O(+) to give O + H + H was carried out at the CRYRING Heavy-Ion Storage Ring in Stockholm. With the stored beam energy of 4.5 MeV, we separated the O signal from the H signals with a differential absorber, thus reducing the problem to a sum of two two-body problems. Results included (1) the ratio of O((3)P) to O((1)D) product, (2) the distribution of recoil-kinetic energy between the two hydrogen atoms, (3) the angular distribution between the hydrogen atoms in the O((3)P) channel and in the O((1)D) channel.

Resonant coherent excitation (RCE) of 390 MeV/u hydrogen-like Ar17+ ions planar channeled in a Si crystal was investigated through measurements of the de-excitation X-rays as well as the charge state distribution of the transmitted ions. We observed enhancements of both the fraction of ionized Ar18+ ions and the intensity of the de-excitation X-rays under the RCE condition. The n=2 states of Ar17+ in the crystal are split into four energy levels due to spin–orbit interaction and Stark effect induced by the planar potential of the crystal. The intensities of the X-rays from the lower two levels were found to be smaller compared with those from the higher two levels, which is explained by the dominance of the 2s component not decaying via a single photon emission. The difference between the resonance profiles of the charge state and the X-ray reflects the nature of n=2 states in the crystal field.

At ultrarelativistic energies, ionization cross sections exceed electron capture cross sections by several orders of magnitude (1,2). Effectively, all electrons transferred to a highly relativistic heavy ion moving in a solid or gaseous target medium are stripped in a relatively short distance. Above ~20 GeV/nucleon, the principal mechanism for electron capture is from pair production (ECPP) (2). The total cross sections for ECPP are te&nically important for making reliable predictions of operating limitations for relativistic heavy-ion colliders, e.g., RHIC and LHC (3). In ECPP, it is expected that ~30% of capture proceeds to excited states of the capturing ion. Some of these relatively weakly bound electrons are radiatively long-lived and easily lost in secondary collisions in solid targets, making measurements of their contributions to total capture experimentally difficult. Electrons lost from high-energy ions in collisions with target atoms form a cusp-shaped spectral peak in the forward direction in the laboratory frame centered at the velocity of the moving ion (4-5). The shape of this electron loss to projectile continuum (ELC) peak has been shown (5,6) to depend on the initial atomic bound state from which the electron is ionized. We have measured and compared ELC electrons from direct ionization of hydrogenlike 33-TeV Pb 81+ (ls) ions (Lorentz factory g = 168) in Al with similar data for electrons created by ECPP for bare Pb 82+ ions in Au - followed by ionization. Both measured ELC peaks are narrow in momentum and angle and very similar in shape.