Fast-electron ejection from C,Ni, Ag and Au foils by <Superscript>36</Superscript><Emphasis Type="Italic">Ar</Emphasis><Superscript>18 + </Superscript> (95 MeV/u): Measurements of absolute cross-sections

Doubly differential electron velocity spectra induced by ³⁶Ar^{18 +} (95 MeV/u) from thin target foils (C, Ni, Ag, Au) were measured at GANIL (Caen, France) by means of the ARGOS multidetector and the time-of-flight technique. The main features observed in the forward spectra are convoy electrons, binary-encounter electrons, and (for the Au target only) a high-velocity tail which we attribute to a Fermi shuttle acceleration mechanism. Backward spectra do not show distinct structures. The spectra allow us to determine absolute singly differential cross-sections as a function of the target material and the emission angle. The convoy electron yield increases with the target atomic number, but for C their yield is so small that our experiment is not able to detect them. Absolute doubly differential cross-sections for binary-encounter electron ejection from C targets are well described by a transport theory which is based on the relativistic electron impact approximation (EIA) for electron production and which accounts for angular deflection, energy loss and energy straggling of the transmitted electrons.Received: 1 July 2003, Revised: 15 December 2003, Published online: 13 July 2004PACS: 34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization) - 79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces - 25.70.-z Low and intermediate energy heavy-ion reactions     

De spectric electroniorum secundariorum prorsus rectorum e corporibus solidis ioniis penetrantibus inductorum

Summary A short introduction into the phenomenon of kinetic ioninduced secondary electron emission from solids is given. The basic features of proton-induced secondary electron spectra from thin foils in forward-(beam-) direction are briefly discussed.

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Summarium Post brevem introductionem in phaenomenon emissionis cineticae electroniorum secundariorum ioniis inductae e corporibus solidis structurae praevalentes spectrorum energiae electroniorum secundariorum ex foliis tenibus protoniis inductorum prorsus rectorum, id est in directionem radii, proponuntur.

     

Strong perturbation effects in heavy ion induced electronic sputtering of lithium fluoride

Electronic sputtering of lithium fluoride by swift heavy ions was studied as a function of electronic energy loss (dE/dx) _e . The single crystal targets were irradiated with swift heavy ion beams (166Z _P 692; 46E _P /M _P (MeV/u) 611). This allowed varying the deposited energy by a factor of 20 (1.86dE/dx (keV/nm) 632). The sputtered secondary ions were measured from well controlled LiF targets without surface contaminations, by means of the time-of-flight technique (TOF-SIMS). The mass spectrum reveals an important contribution of clusters (over single ions), which increases with (dE/dx) _e . Another observation for the strongest perturbation at high dE/dx (>8 keV/nm) is that the secondary ion yields saturate: Y(dE/dx) = constant. In contrast, at lower dE/dx (<8 keV/nm) for weaker perturbation, the yield Y scales with (dE/dx)². This quadratic increase would rather point towards a thermal evaporation-like mechanism leading to electronic sputtering, however, the origin of the yield saturation remains an open finding.     

Experimental study and Monte Carlo simulation of the correlation between electron emission and stopping power for swift proton impact on amorphous carbon target

It is usually well accepted that for swift protons, the induced backward and forward electron emission yield is proportional to the projectile electronic stopping power. This was observed in particular for thin amorphous carbon foils. However, this law was established from a non extensive set of experimental data and somewhat confirmed by rough macroscopic theories. We then developed a standard Monte Carlo simulation to predict the yield dependence on proton energy [0.5–10 MeV] and for a wide range of foil thickness. After evaluating the reliability of this simulation, we showed and explained why the law of proportionality cannot generally hold for forward electron emission. In particular, the ratio between forward yield and stopping power generally depends on foil thickness and proton energy. We performed a new experiment that confirmed our theoretical predictions. Received 9 March 2001     

Electron loss and capture to continuum from He and Ne atoms bombarded with He+-Ions

We have measured the cusp electron yield in coincidence with the transmitted charge state (He⁰, He⁺ and He⁺⁺) when³He⁺ collides with He and Ne under single collision conditions. For the first time this enables the electron capture to the continuum (ECC) yield to be directly compared with that from electron loss to continuum (ELC). While the ECC contribution is smaller than that from ELC at high projectile velocities (V _p >3 au) the data suggest that ECC will dominate belowV _p =2.8 au. The relevance of the results to the projectile velocity dependence of existing capture theories is discussed.     

Equilibrium convoy electron production and charge exchange

RatiosN _2s /N _3p of 2s to 3p populations in hydrogen atoms formed by the passage of protons through carbon foils have been measured using the beam-foil-laser excitation method reported very recently. No dependence ofN _2s /N _3p on the incident proton energyE _p , in the 100–300 keV energy range analysed, is observed. From the ratioN _3p /N _2p of 3p to 2p beam-foil populations in hydrogen reported previously (N _3p /N _2p independent ofE _p forE _p >100 keV) and the ratiosN _2s /N _3p measured in the present work, a mean value ofN _2s /N _2p equal to 0.61±0.04 is deduced. These results are compared with available experimental data.