Ion slowing down and charge exchange at small impact parameters selected by channeling: Superdensity effects

Abstract

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions

“…First, let's consider the collision system Pb 56+ at 28.9 MeV u -1 on silicon, a target that corresponds to an increase of the perturbation K p parameter of about 2.2. From figure 13, we can observe that a clear improvement is also achieved over the whole charge state distribution when using ETACHA4 instead of ETACHA23 and comparing to experimental data obtained under a random orientation of a silicon crystal of effective thickness 1.1 µm [45], i.e. a target thickness of 327 µg cm -2 .…”

Using channeling properties for studying the impact-parameter dependence of electron capture by 20-MeV/u uranium ions in a silicon crystal

“…Finally we have shown in ref. [18] that even the ions with very high transverse energy, do not show up the sharp components of the L-lines. As these ions approach enough atomic strings to suffer L-shell ionization, this result proves that the filling of the L-shell takes place much less rapidly than for unchanneled ions.…”

“…In order to really compare the experimental and theoretical results for impact parameters b > 0.25 Å, we have evaluated the projectile ionization probability to deduce a theoretical probability for effective capture for electron impact ionization of the projectile n-shell to the radiative decay times and to the decay branching ratios that correspond to the probability for an electron initially on a n-shell to reach a n'-shell with n'<n. The cross sections [18] and a scaling law based on the Lotz formula [30]. The radiative decay time and the branching ratio have been obtained from the calculations of Omidvar for H-like ions (with a Z p -4 scaling law for the decay times) [31].…”

Impact of high-energy cosmic-ray protons and ions on the elements of spacecraft on-board devices

“…The fea tures of particle motion in the crystal with dimension less transverse energies ε ⊥ that exceed the critical value for channeling ε ⊥cr (ε ⊥cr = 2) should be carefully con sidered. So, in a number of works, it is shown theoret ically [34,35] and experimentally [36,37] that for ε ⊥cr < ε ⊥ < 20 a mode exists that is, in fact, opposite to channelling, for which inelastic processes occur at a rate exceeding the values characteristic of an amor phous body or, which is the same, for random motion in the crystal (Fig. 9, 10).…”

“…Experimental energy loss spectra for a noncolli mated beam of high energy protons in a semiconductor crystal: the window w 1 shows decreased losses during channeling; the window w 2 is a broad spectrum with dis persion exceeding the average values by two times[37].…”