An experimental setup is described, which is used to multi-ionize neutral clusters and to study their stability and the importance of different decay processes. Clusters are ionized in collisions with slow multiply charged ions (projectile charge z ranging from 1 to 30, kinetic energies ranging from 1 to 20 keV/charge). Both ion and cluster beamlines, as well as the characteristics of the analysis and detection systems, are described. Collisions with highly charged ions such as Ar8+ or Xe30+ turn out to be efficient tools in preparing clusters in high charge states without increasing significantly their internal temperature. Measurements performed in coincidence with the number of electrons stabilized by the projectile ion after the collision allowed us to control the charge and the excitation energy of the ionized system. The efficiency of the method is demonstrated for sodium clusters and C60 molecules.

We discuss the Coulomb fragmentation of highly charged metal clusters. The analogy with a classical conducting liquid drop is assessed from molecular dynamics calculations. Experimentally, the highly charged metal clusters are formed in collisions with highly charged ions (Xe20+, Ar11+, Ar8+, Ar3+, and O5+) at low velocity. We show new experimental data on the rate of emitted light charged particles that indicate an as yet unobserved fragmentation regime. Collisions of ions with metal clusters also offer a unique method to strongly excite the conducting electron gas within a short time of a few fs opening the possibility to study large amplitude electron dynamics and relaxation in microscopic systems.

Highly charged ions provide a unique way to prepare metal clusters in such high charged states that it has opened the possibility to undertake detailed investigations of the dynamics of strong Coulomb instabilities and subsequent fragmentation of charged conducting microclusters. Experimentally, a neutral atomic cluster beam is intersected by a low velocity HCI beam (Xe30+, Xe20+, Ar11+, Ar8+, Ar3+, and O5+) and resulting charged cluster fragments are analysed. We have selected some new experimental data that bear evidence of the efficiency of the method and of the existence of an as yet unobserved fragmentation regime.

Differential cross sections for the elastic scattering of electrons by multiply charged ions have been measured at scattering angles between and . Mainly at backward angles the cross section deviates remarkably from the Rutherford cross section showing oscillations due to the structure of the ionic core. Experimental results obtained for ions and different ions are found to compare well with theoretical calculations.

The electronic excitation of alkali-metal clusters by low-energy ions is investigated experimentally for the first time. Multi-ionized clusters possibly undergoing Coulomb dissociation are formed and detected. Free sodium clusters of a few hundred atoms have been bombarded by different ion beams ( H +, O 5+, Ar 8+) of velocity ranging from 0.2 to 0.9v0. The mass/charge ratio of charged outgoing clusters is measured by a time-of-flight spectrometer of high resolution [Formula: see text]. Critical sizes for stability against charge excess have been deduced for cluster charges up to 6. Temperature effects on critical sizes are observed, and they reveal two distinct regimes: electron transfer in peripheral collisions with multicharged ions leading to “cold” highly ionized clusters and strong electronic excitation in central collisions subsequently followed by multielectron emission.

Neutral sodium clusters (Nan, n ≤ 800) have been ionized in collisions with different ion beams (H+, O5+, Ar8+) at collision energies between 1 and 19 keV per charge. From an analysis of the measured mass / charge spectrum critical sizes for multiply charged clusters are deduced and compared with those obtained by laser-ionization. The dominant ionization mechanism depends on the charge state of the projectile. For highly charged ions the multi-electron capture process leads to the formation of relatively “cold” multiply charged clusters; in the proton case multiple ionization is discussed in terms of electronic excitation followed by electron evaporation on a sub-nanosecond time scale.

Differential cross sections for electron impact excitation of magnesium like Ar6+ ions (3s(21)S-3s3p(1)P) have been measured at collision energies between 27 and 100 eV. For the first time, the experimental studies have been extended towards backward scattering angles. When lowering the collision energy the maximum in the excitation cross section is shifted to angles > 90 degrees; backward scattering becomes dominant as predicted by theory.

The multiple ionization of alkali-metal clusters by low energy ions is investigated experientially for the first time. Multi-ionized clusters possibly undergoing Coulomb dissociation are formed and detected. Free sodium clusters of a few hundred atoms have been bombarded by different ion beams ( ${\mathrm{H}}^{+}$, ${\mathrm{O}}^{5+}$, ${\mathrm{Ar}}^{8+}$) of velocity ranging from $0.5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ to $2.2\ifmmode\times\else\texttimes\fi{}{10}^{8}\mathrm{cm}/\mathrm{s}$. Critical sizes for stability against charge excess have been deduced for cluster charges up to 6. They are found to depend upon the projectile charge. Observed differences are discussed in terms of temperature effects.

Differential cross sections for electron impact excitation of magnesiumlike Ar6+ ions (3s21S-3s3p 1P) have been measured at collision energies between 27 and 100 eV. For the first time, the experimental studies have been extended towards backward scattering angles. When lowering the collision energy the maximum in the excitation cross section is shifted to angles > 90°; backward scattering becomes dominant as predicted by theory.

Differential cross sections for the elastic scattering of electrons by multiply charged ions have been measured in a crossed‐beams device. They are compared with theoretical predictions obtained within the framework of a Hartree Fock calculation. Results are discussed for the ionic systems Ba2+ and Xe6+ for electron energies below 50 eV and scattering angles between 30° and 80°. Owing to the structure of the ionic core the differential cross sections deviate strongly from the Rutherford cross section but show good agreement with the theoretical predictions.

Antiproton induced fission probabilities of U-238, Bi-209, Pb-208 and Au177 are reported together with the mass distribution of the fission fragments in the U-238 and Bi-209 cases. The charged particles multiplicities observed in coincidence with fission have, also, been measured for U and Bi and are presented.

A new crossed beam apparatus has been developed for measuring differential cross sections for the excitation of multiply charged ions by electron impact. First results have been obtained for sodium-like Argon (Ar 7+); the 3s–3p transition with an excitation energy of ~ 17.5 eV has been studied at an electron energy of 100 eV. The preliminary experimental values are compared with theoretical results obtained within a Born-approximation.

Coincidences between high energy light particles emanating from 35A MeV 12C +C, Al and Cu collisions show a significant in-plane excess. This excess increases with the mass of the coincident particles and decreases with the mass of the target. Momentum conservation effects within a participant region reproduce the main features of the observed correlations. Data from 85 A MeV reactions show similar trends and are also well described by the same momentum conservation effects.

Differential cross sections have been measured for the electron-impact excitation of a multiply charged ion. In a crossed-beam experiment the resonant 3s-3p transition of sodiumlike Ar7+ is studied at an electron energy of 100 eV in an angular range between 13-degrees and 29-degrees. The experimental cross sections are found to be in good agreement with theoretical predictions obtained in Coulomb-Born distorted-wave approximation.

Inclusive spectra of p, d, t, 3He and 4He from 35A MeV 12C + C, Al, Cu, Au reactions, as well as coincidences between projectile-like fragments and light particles have been measured. The apparent temperature does not seem to depend on the size of the coincident fragment. An independent way to determine source velocities indicates that high-energy protons are emitted from a source with a velocity close to half the beam velocity, even in asymmetric reactions. We observe an in-plane enhancement in the azimuthal angular distributions of coincident projectile-like fragments, which gets stronger with increasing mass of the triggering particle or the fragment. A discussion around momentum conservation effects shows that p * B correlations may originate from a combination of pure projectile breakup and nucleon-nucleon quasi-elastic scattering processes. The correlations observed in less peripheral collisions need the introduction of a second, light-particle emitting source.

The angular and velocity distributions of incomplete fusion residues have been measured, around 30 AMeV projectile incident energy, for a number of systems with varying mass asymmetries, from the most asymmetric S+Cu, to the almost symmetric Ar+Ca. The main experimental finding is that the parallel width of the velocity distribution increases sharply for decreasing asymmetries, while the perpendicular width remains nearly constant. Using, as data, the widths and mean values of the velocity distributions, it was possible to derive the number of preequilibrium particles emitted by the projectile and by the target. It was found that target emission becomes noticeable only when the center of mass velocity of the target, at nuclear contact, exceeds approximately 2.5 cm/ns. This underlines the relevance of the center of mass velocities in the preequilibrium emission and incomplete fusion processes.

Double differential cross section for high energy photon production have been measured for proton-nucleus reactions at 168 and 200 MeV. A comparison is made with previous measurements at 140 and 197 MeV. Calculations are performed assuming that first chance neutron-proton bremsstrahlung is the main production mechanism. Two different approaches of the elementary process are tested in this paper.

A 4π-multidetector consisting of 140 CsI(Tl) detectors has been designed and built to be used for detecting and identifying either light charged particles (with a detection threshold of about 0.4 MeV/nucleon) and neutrons or light heavy ions and light charged particles, in the range of energies available at SARA (from 10 to 40 MeV/nucleon). The choice of the scintillator material is discussed and a description of the mechanical and electronic design is given. First experimental results obtained with this device are presented.

Double differential cross sections for high energy photon production have been measured for proton-nucleus reactions at 72 MeV. The experimental data suggest that first chance incoherent proton-neutron bremsstrahlung is the main production mechanism. A comparison is made with theory and with the available data at 140 MeV.