High resolution Auger spectroscopy in energetic ion atom collisions

A Monte Carlo approach was applied for simulations of the early stage (first tens of femtosecond) of kinetics of the electronic subsystem of silica $({\text{SiO}}_{2})$ in tracks of swift heavy ions (SHIs) decelerated in the electronic stopping regime. At the first step multiple ionizations of target atoms by a projectile (${\text{Ca}}^{+19}$, $E=11.4\text{ }\text{MeV}/\text{amu}$) were described that gave the initial spatial distributions of free electrons having different momenta as well as distributions of holes in different atomic shells. Spatial propagation of fast electrons results in secondary ionizations of target atoms as well as in energy transfer to the lattice at times much shorter than the times of atomic oscillations (phonons). The well detected front of excitation in the electronic and ionic subsystems is formed due to this propagation which cannot be described by models based on diffusion mechanisms (e.g., parabolic equations of heat diffusion). At times $\ensuremath{\sim}10\text{ }\text{fs}$ after the projectile passage, about $\ensuremath{\sim}0.1\mathrm{%}$ of the energy is already transferred to the lattice. About 63% of the energy deposited by the ion is accumulated in holes at these times. Calculated distributions of these holes through the atomic shells are in excellent agreement with the spectroscopy experiments. Comparison with these experiments demonstrated also that relaxation of the electronic subsystem in SHI tracks in solids cannot be described adequately without taking into account intra-atomic and interatomic Auger (Knotek-Feibelman) processes.

Early stage of the electron kinetics in swift heavy ion tracks in dielectrics

Publisher Summary This chapter reviews the understanding of the process of K-shell vacancy production in ion–atom collisions. It is necessary to discuss the role of K-shell electron transfer along with excitation and ionization processes as the mechanisms of removing the K-shell electrons. The chapter presents ionization in a one-to-one context with the K-shell electron transfer process for collisions from the very asymmetric systems, where ionization is the dominant K-vacancy production mechanism, to near-symmetric systems, where K-electron transfer is the dominant mechanism. Experimental data from heavy-ion collisions are presented in parallel to selective data from the simple collisions such as H+ + H and H+ + He. This is important in view that many theoretical models have been developed originally for simple collision systems. Because of the range of parameters that can be controlled in heavy-ion collisions, heavy-ion collision data provide new grounds for testing these and some new theoretical models. The chapter presents a review of the experimental methods of measuring K-shell vacancy production cross sections and measurements where excitation, ionization, and charge transfer cross sections can be identified. The status of the theory of electron transfer in ion–atom collisions is reviewed and comparisons between theories are discussed in the chapter.

Inner-Shell Vacancy Production in Ion–Atom Collisions

The simple geometrical model we developed recently for ionization probabilities on the basis of a geometrical BEA picture is generalized and extended to take into account magnetic substates and non-zero impact parameter ion-atom collisions. Ionization probabilities per electron for the L shell and separately for the 2s and 2p Subshells of neon in 5.1 MeV/u N+ and N7+ as well as 5.5 MeV/u H+ collisions were determined from 0.8−1 eV resolution K-Auger spectra. Anisotropy parameters of KL-LL23L23 satellite lines were determined in 5.5 MeV/u Ar6+, Ne10+ and 5.1 MeV/u N2+ collisions. The comparison of the extended model with the experimental data shows a good agreement. The model seems to be able to give account of the dependence of the ionization probability on quantum numbers l and m. Comparing the results with a wide range of experimental data no contradictions were found with the universal scaling features predicted by the model. By analyzing the impact parameter dependence of ionization probabilities the validity of the model was estimated to break down at ν1 ≈ ν2/3 towards lower impact velocities.

A simple theoretical approach to multiple ionization and its application for 5.1 and 5.5 MeV/u Xq++ Ne collisions

K X-ray transitions in highly charged neon recoil ions have been observed in collisions of 1.4 MeV/amu Ar12+, 14+, Ni16+, Kr18+, Xe24+, Pb36+ and U40+ with a neon gas target. The spectral lines are attributed to excited states of Ne9+, Ne8+ and Ne7+. Experimental evidence is given for a secondary selective electron capture into outer shells of fully stripped slow target ions.

http://iopscience.iop.org/article/10.1088/0022-3700/13/12/020/pdf

K X-ray transitions from highly charged very slow Ne recoil ions produced by 1.4 MeV/amu very heavy ion impact

Projectile dependence of single- K multiple- L shell vacancy production in argon: A universal scaling of 〈 l 〉

Measurements of the target-thickness dependences of the target $K$ x-ray production yields are reported for 1.7-MeV/amu ${\mathrm{F}}^{q+}$ ($q=6, 8, \mathrm{and} 9$) ions incident upon thin solid targets of elements from Ti to Co. Target $K$ x-ray production cross sections were extracted in the limit of vanishing target thickness. Comparisons of the data to theoretical estimates based upon combinations of direct ionization and electron-transfer processes are presented. Projectile $K$-vacancy production and quenching cross sections were obtained from the three-component model for the target $K$ x-ray data as a function of foil thickness. Comparisons of the projectile parameters to theoretical estimates based upon electron transfer, direct ionization, and excitation processes are presented.

B. L. Doyle

Papers

Projectile dependence of single- K multiple- L shell vacancy production in argon: A universal scaling of 〈 l 〉

Target and projectile cross sections for F ions on Ti, V, Cr, Fe, and Co: 1.7 MeV/amu