Multiple electromagnetic excitation with relativistic heavy ions

The multiple electromagnetic excitation with fast projectiles (heavy ions) is studied theoretically in the sudden approximation. Of special interest is the excitation of rotational states coupled to giant (dipole) vibrations. Closed form expressions are obtained for the excitation of a rigid rotor. The strong pulse of high energy equivalent photons in relativistic heavy ion collisions opens up new possibilities for nuclear structure studies, not possible e.g. with electron scattering or nuclear Raman scattering. It is also pointed out that the “Brink-hypothesis” can be investigated in a new way by means of multiple electromagnetic excitation with relativistic heavy ions of low lying states coupled to the giant dipole mode.     

Loss of electrons from fast heavy structure ions colliding with atoms

Nonperturbative theory is developed for the multiple ionization of fast heavy structure ions colliding with neutral complex atoms. The cross sections for multiple loss of electrons by structure uranium ions U¹⁰⁺ (loss of up to 82 electrons) and U²⁸⁺ (loss of up to 64 electrons) colliding with argon atoms are calculated. The results are compared with available experimental data.     

Application of a uniform semiclassical theory to the multiple Coulomb excitation of heavy ions

Transition probabilities of classically allowed multiple Coulomb excitation of deformed heavy nuclei induced by heavy ions are calculated within a uniform semiclassical approximation. It is found that a Bessel uniform approximation is necessary and that caustics have to be treated carefully.     

A fast calculation of excitation autoionization cross-sections of Na-like ions

In this work, based on the calculation in detail, two new fitting formulae of total excitation and excitation autoionization cross-sections for Na-like ions (18?Z?39) are given. For discussing the variation of the total excitation autoionization cross-section, a systematic study of the dependence of the overall branching ratio on incident electron energy and nuclear charge is also carried out.     

On a fragmentation mechanism of relativistic heavy ions

A model is proposed describing main features of a behaviour of the fragmentation cross sections for relativistic ions including their relative yields. The reaction is assumed to proceed in two stages: At the first one the ion is excited by the peripheral collision with a nucleus, at the second one it decays statistically in flight with emitting a fragment. A strong analogy is demonstrated for the process with the corresponding reactions of nonrelativistic ions.     

Biomolecule desorption yields as a function of the angle of incidence of fast heavy ions

A time-of-flight mass spectrometer that allows variation of the angle of incidence of the primary ion beam in desorption experiments has been developed. It has been used with heavy-ion beams of MeV energies from the Uppsala EN-tandem accelerator in order to study the yield of molecular ions from samples of ergosterol, glycylglycine and cesium iodide. The general behaviour of the angular distributions is that the yield increases sharply when oblique incidence is approached. The shape of the angular distribution for ergosterol ions is found to depend on the stopping power of the primary ion. The results are discussed in terms of thermal spike models for the desorption process.     

Energy losses of fast heavy structure ions in multiple collisions with diatomic molecules

The nonperturbative calculations of the effects of multiple collisions and the orientation of the molecule axis with respect to the projectile motion direction in the energy losses of fast heavy highly charged structure ions colliding with diatomic molecules have been performed with allowance for various excitations and the ionization of both the projectile and target. It has been shown that the effects of multiple collisions gives rise to a significant difference between the energy losses at the parallel and perpendicular orientations of the target; this effect is insignificant for chaotic orientation. Conclusions for the cross sections for the stripping of hydrogen-like ions are similar.     

Studies of neonL-shell excitation by impact of highly ionized heavy ions

Passage of foil-excited 1.4 MeV/A S and 1.1 MeV/A Cl ions of neon charge state ～ 12⁺ through neon gas targets at pressure ～100 mTorr has been found to be accompanied by copious production of Ne II–VIII excited states. Comparable excitation cross-sections ～10^?18 cm² are found for a large number of levels belonging to all of these charge states and corresponding to principal quantum numbersn=2, 3, 4. Vacancy distributions very similar to those found in beam-foil excitation of ～1MeV neon beams are found. Because the Ne recoil velocities are small compared to the fast beam velocities characteristic of the beam-foil source, it is possible to reduce both Doppler shifts and spreads by 3–4 order of magnitude for equivalent collimation. It has also been found that there is an excitation cross-section change of a factor ～5 for a corresponding projectile charge state change from 6⁺ to 12⁺, that efforts to classifyK x-ray satellite spectra byLshell vacancy labels (KL ⁰,KL ¹,...) are probably inaccurate due to extensive population ofn≧3 spectator levels, that both the recoil ion and beam-foil spectra exhibit few lines withn≧4, and that for the allowed transitions studied here, collisional excited states quenching effects due to the ～100mTorr target gas pressures used are negligible.     

The contribution of nuclear inelastic excitation to the optical potential for heavy ions

Using the plane-wave approximation we derive analytical expressions for both the real and imaginary parts of the polarization potential arising from nuclear inelastic scattering. These potentials and the resulting elastic and inelastic cross sections are compared with exact coupledchannel calculations for ¹³C on ⁴⁰Ca at 68 MeV. The agreement, for the most part, is good. We also briefly discuss the numerical non-local potentials for this system and the imaginary polarization potential for ¹⁶O on ²⁰⁸Pb at 104 MeV.     

VUV-luminescence and excitation spectra of the heavy trivalent rare-earth ions in fluoride matrices

VUV 4f ⁿ → 4f^n?15d transitions of Gd³⁺, Er³⁺, Tm³⁺, and Lu³⁺ in fluoride matrices have been analyzed with high-resolution luminescence and excitation spectroscopy. In trifluorides, strong electron-phonon coupling has been found. In the other matrices, the luminescence spectra clearly yield zero-phonon lines and phonon replica, indicating intermediate coupling. The energies of the zero-phonon lines observed are compared with theoretical predictions. Near the threshold of f → d excitations, some of the excitation spectra yield sharp structures which cannot be explained with phonon replica but will be discussed in terms of the energy levels of the 4f^n?15d configuration.     

Multiple electron loss by structured heavy ions in fast collisions with complex atoms

A nonperturbative theory of multiple ionization of heavy structured ions in fast collisions with complex neutral atoms is developed. Cross sections are calculated for multiple loss of electrons (up to 15) in collisions of U¹⁰⁺ and U²⁸⁺ with argon atoms and nitrogen molecules. The results are compared with experimental data.     

Mach cones induced by fast heavy ions in electron plasma

Fast heavy ions penetrating through solids initiate density oscillations of the electron plasma, forming Mach cones if the projectile velocity exceeds a critical valuec _s . These Mach waves should lead to the directed emission of electrons from the target. The preferential emission angle? as a function of the bombarding energy is calculated for various projectile-target combinations.     

Investigation of thermal processes in single crystals irradiated with high-energy heavy ions

The thermal processes arising in InP and GaAs single crystals irradiated with high-energy heavy ions are investigated with the help of a thermal peak model. Numerical simulation is used to estimate the sizes of regions where the melting process can occur and the structural changes arising in the irradiated materials are observed.     

On the nuclear interaction potential in the reactions with heavy ions

The interaction potential of heavy ions⁴He,⁶Li,¹²C and¹⁶O is constructed in the folding model. The density distribution of nuclear matter for these nuclei is calculated in the framework of the hyperspherical function method. For the calculation of the folding potentials we have employed the Skyrme nucleon-nucleon forces. The influence of several effects on the results of calculations is studied: the role of the three-body forces of the nucleon-nucleon interaction, dependence of the folding potential on the mass numbers of the colliding nuclei and the possibility of observing the monopole resonance in the ion inelastic scattering. Using our folding potential as a real part of the optical potential we have calculated the differential cross section of elastic scattering of⁶Li from¹²C at laboratory energy of lithium ionsT _L =90.0 MeV. Reasonable agreement with experiment is obtained.     

Effective stopping of fast heavy highly charged structure ions in collisions with complex atoms

The nonperturbative theory of the energy losses of fast heavy highly charged structure ions colliding with neutral complex atoms is developed with allowance for simultaneous excitations of the electron shells of an ion and an atom. Formulas for effective stopping that are similar to the Bethe-Bloch formulas have been derived. As an example, the energy losses of partially stripped uranium ions colliding with argon atoms are calculated.     

Energy losses of fast heavy multiply charged structural ions in collisions with complex atoms

A nonperturbatve theory of energy losses of fast heavy multiply charged structural ions in collisions with neutral complex atoms is elaborated with allowance for simultaneous excitations of ionic and atomic electron shells. Formulas for the effective deceleration that are similar to the well-known Bethe-Bloch formulas are derived. By way of example, the energy lost by partially stripped U ^q+ ions (10 ≤ q ≤ 70) colliding with argon atoms and also the energy lost by Au, Pb, and Bi ions colliding with various targets are calculated. The results of calculation are compared with experimental data.     

Interplay of charge exchange and projectile excitation in the stopping of swift heavy ions

The electronic energy loss of a dressed ion penetrating through matter is commonly considered as being synonymous with the sum of the excitation energies of the target and the projectile in atomic collisions undergone during the passage. We show that this is not justified in projectile-ionizing collisions and discuss some consequences. Received 23 October 2002 / Received in final form 1st December 2002 Published online 18 February 2003