Charge States and Charge-Changing Cross Sections of Fast Heavy Ions Penetrating Through Gaseous and Solid Media

“…Indeed, the ion charge state changes from its initial value q ini to a mean value q mean ðlÞ as a function of the path length l inside the solid. The charge-state equilibrium for such fast ions is determined by the balance between electron capture and electron loss rates, during penetration in the bulk (decay processes are not so important) [19]. For thin films, the condition q mean ðlÞ % q ini can be achieved throughout the entire layer.…”

mentioning

confidence: 99%

Direct Evidence for Projectile Charge-State Dependent Crater Formation Due to Fast Ions

et al. 2008

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We report on craters formed by individual 3 MeV=u Au q ini þ ions of selected incident charge states q ini penetrating thin layers of poly(methyl methacrylate). Holes and raised regions are formed around the region of the impact, with sizes that depend strongly and differently on q ini . Variation of q ini , of the film thickness and of the angle of incidence allows us to extract information about the depth of origin contributing to different crater features. DOI: 10.1103/PhysRevLett.101.167601 PACS numbers: 79.20.Rf, 61.80.Jh, 61.82.Pv, 81.16.Rf Energetic atomic [1-3], molecular or cluster ions [4] impacting solids may leave tiny holes at the surface often surrounded by a raised region of displaced material. The observed surface morphology [1][2][3][4] is similar to what is found in ablation craters produced by an intense laser pulse [5,6], in macroscopic craters produced by meteorite impacts on planets [7], or by balls dropped into granular media [8], although their spatial scales may differ by about 17 orders of magnitude. Depending on the energy regime of the ions and the type of material being bombarded, the shape of the impact features and the underlying mechanisms of formation may differ [9,10]. As the energy deposited by swift ions of equal kinetic energy, but different charge-states may vary substantially close to the surface, a detailed knowledge of charge-state dependent effects is of great importance for ion-beam based techniques of materials structuring (such as ion-track etching), particularly considering the new demands for smaller pattern sizes and the use of thinner layers [11]. Our results give direct evidence for a strong dependence of the surface modifications introduced by single fast ions on their charge state. For track-etching procedures, this means it is possible to control the etching sensitivity at the surface and charge equilibration below the surface should yield different etched shapes, dependent on the incident charge state. Moreover, by employing a series of well-defined nonequilibrium charge states, we could derive depth information on the near-surface effects induced by single fast ion impacts.In this Letter, we focus on cratering induced by high velocity ions. At specific kinetic energies of a few MeV per nucleon, such ions transfer more than 99% of their energy to the target-electron system. A considerable fraction of the energy deposited in the track of a swift heavy ion is concentrated in a core region ( % 1 nm), where ionizations are directly produced by the ions. Fast secondary electrons spread the rest of the energy over larger distances. The exact size of such regions depend on the material and on the velocity of the ions, while the total amount of energy loss per path length, S e ¼ dE e =dx, is well understood [12]. The subsequent electron dynamics, however, is a nonlinear phenomenon and it may result in large sputter yields and cratering, due to the coupling of electronic and atomic degrees of freedom [13][14][15]. For reviews on ion-induced electronic cratering pr...

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“…The dominant process in electron capture into the 2s shell is non-radiative capture of continuum electrons (Coulomb charge transfer). The cross section for radiative electron capture of continuum electrons is only of the order of 102 b [15]. Radiative decay of bound electrons and Coster-Kronig transitions are improbable.…”

Section: F(t) =mentioning

confidence: 99%

Anomalously large transient field through polarized electron capture

et al. 1975

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The measured precession for 2aSi(2~) recoiling into magnetized Fe shows an anomalous increase with initial recoil velocity. This is explained quantitatively by capture of polarized Fe electrons into 2s vacancies in the moving ion.Transient magnetic fields have been used for the determination of g-factors of short-lived excited states of nuclei recoiling into ferromagnets [1][2][3]. In these measurements the magnitude of the transient field was estimated by adjusting the Lindhard and Wmther (LW) theory [4], which treats the scattering of (polarized) electrons by an ion on slowing-down in a polarized ferromagnet. For realistic screening and the known polarized electron velocity Up in the ferromagnet (but ignoring possible atomic effects) the theory yields fields, which are a factor of two lower than found experimentally [4], although the dependence on the charge Z of the nucleus on recoil into Fe is well reproduced.Most experiments involving the transient field were carried out at relatively low recoil velocities (o/c < 1.6%). The velocity dependence of the transient field in Fe has been tested in three experiments. For 196pt [5] and 103Rh [6] barely significant deviations from the adjusted LW theory were observed at a recoil velocity o/c = 1.8%. For 56Fe [7], however, large anomalies were found at o/c = 3% but the deviation was attributed to radiation damage effects.Several recent experiments [8, 9] on light nuclei (A = 18) at higher recoil velocities yielded integral precessions twice as large as expected from the adjusted LW theory (ALW) but the nuclear lifetimes were too long (3-7 ps) to exclude the possibility of (large) static hyperfme fields explaining the deviation.The possibility of an anomalous transient field was investigated in the present work for 28Si recoiling into polarized Fe at three initial velocities. The recoils were produced by inelastic proton and wparticle scattering at the bombarding energies shown in ta- The high-velocity point deviates by four standard deviations and by a factor of three from the LW curve. 329

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Charge States and Charge-Changing Cross Sections of Fast Heavy Ions Penetrating Through Gaseous and Solid Media

Cited by 1,043 publications

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Sassy, a gas-filled magnetic separator for the study of fusion reaction products

Sassy, a gas-filled magnetic separator for the study of fusion reaction products

Direct Evidence for Projectile Charge-State Dependent Crater Formation Due to Fast Ions

Anomalously large transient field through polarized electron capture

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