For an accurate calculation of target x-ray production or of projectile energy loss in low-Z materials, it is necessary to know the projectile charge state at each point in the material. If the projectile is fast enough so that charge transfer can be neglected with respect to electron stripping, it is possible to deduce a simple expression for the charge fractions as a function of the penetration distance into the target. The expression depends essentially only on the stripping cross section per electron of the particular shell being stripped, on the initial number of electrons on the projectile, and on the charge state. A small correction has to be applied for the effect of shells lying inside of the shell being stripped. The expression has been tested with Xe45+ projectiles between 82 and 300 MeV/u and with U83+ projectiles between 105 and 960 MeV/u with targets of Be, C, mylar, and Al. Model calculations are made of the effect of charge distributions on PIXE x-ray production and on projectile energy loss.

When a swift charged particle enters a materials medium it will interact with the electrons and nuclei in the medium and begins to lose energy as it penetrates into the medium. The interaction can be generally thought of as collisions between the charged particle and either the atomic electron or the nucleus (considered separately). The energy given off will result in ionization, production of ion-electron pairs, in the medium; also it can appear in the form of electromagnetic radiation, a process known as bremsstrahlung (braking radiation). We are interested in describing the energy loss per unit distance traveled by the charged particle, and the range of the particle in various materials, the latter being defined as the distance traveled from the point of entry to the point of being essentially rest. A charged particleis called ‘heavy’ if its rest mass is large compared to the rest mass of the electron. Thus mesons, protons, α -particles, and of course fission fragments are all heavy charged particles. By the same token, electrons and positrons are ‘light’ particles. If we ignore nuclear forces and consider only the interactions arising from Coulomb forces, then we can speak of four principal types of charged-particle interactions:

We shall report on the recently observed dependence of the lifetime of the first excited state in 125Te on the ionic charge state. Then we shall give an interpretation of the dependence of the half-life in terms of a new type of nuclear internal conversion without emission of the electron into the continuum of electron energies. We have named this process internal conversion between bound atomic states or BIC. The resonant character of the BIC will be established and the main parameters governing the decay process will be discussed [1–3].

A gaseous cell to study heavy-ion collisions with atomic hydrogen was made with the aim of investigating charge-exchange collisions in the intermediate-to-high velocity regime. The method of thermal-dissociation in a tungsten-tube furnace was used. The operating characteristics of the partially dissociated hydrogen target, which depend not only on the design of the furnace but also on the collision-chamber geometry and pumping system, are described. The absolute calibration of the target cell was performed using double capture of C3+ at 1.1 MeV and elastic scattering of the He-0 at 1.0 MeV in the mixture of H and H-2. At temperatures of about 2600 K, a degree of dissociation of 80% was obtained with the tungsten filament lasting typically more than 300 h of operation. (C) 1997 Elsevier Science B.V.

In the last decade a great advance has been obtained in the understanding of mechanisms leading to the electron loss process by multiply-charged ions. In particular, the electron-electron contribution to electron loss has been extensively studied and its connection with the electron-ion ionization process has been established, both theoretically and experimentally. In this paper we use recent experimental results obtained by Sant'Anna et al. from C3+ collisions On atomic Hydrogen to obtain the electron ionization cross section of C3+ ions. A comparison with results obtained directly from crossed-beams experiments indicates that electron-loss collisions can give a simple and reliable alternative way to obtain electron ionization cross sections of multiply-charged ions.

The authors have measured electron capture and electron loss cross sections of C{sup 3+} and O{sup 5+} ions on He, Ne, Ar, Kr and Xe in the 1.0 to 4.0 MeV energy range. For both processes the authors observed a strong saturation in the target Z dependence of the cross sections which occurs for the whole range of measured energies. In the case of electron loss, there is also a clear indication of the influence of the electronic structure of the target in the measured cross sections. This can be a signature of the role played by the e-e interaction (antiscreening) in collisions with multielectron targets as indicated by a similar behavior appearing in first-order calculations of this process. As the theoretical estimate of the n-e contribution to electron loss involves non-perturbative calculations, the relative contributions of the n-e and e-e contributions for heavy targets is not known at present.

Using a grazing emission method, we have made measurements of 22.6-GeV electron impact ionization cross sections at the front and back faces of ∼ 70-µm thick Al and Cu foils. These give, respectively, the cross sections without and with a density effect predicted by Fermi. For Cu, the back cross section ratio at 22.6 and 5.1 GeV (previously measured) is 1.00±0.04, confirming the predicted energy independence of this cross section. The absolute cross sections agree overall with theoretical calculations.