The concept of treating the penetration of energetic ions through solids in the context of the physics of binary atomic collisions requires some initial consideration. Clearly atomic collision processes which occur at distances larger than interatomic spaces in solids are difficult if not impossible to treat on a purely binary basis; on the other hand as the velocity of the penetrating ion increases, many processes involving these large impact parameters become less dominant and an atomistic treatment becomes more relevant. In the case of elastic scattering, for example, the large impact parameter effects upon deflection by atomic cores and the energy transfer to target atoms decrease with increasing projectile velocity. For collisions which lead to inner-shell ionization, the impact parameters are so small that the presence of the target atom in a solid medium will have hardly any effect except insofar as the state of the projectile ion is altered by its previous collision history in the solid. The approach then is to apply our knowledge of single collision atomic processes to the anticipated results of a sequence of binary processes.

Atomic collisions in solids

The measurement techniques of beam-foil spectroscopy are reviewed. These comprise the study of wavelengths of heavy ions with low and high charge states at visible, UV and X-ray wavelengths from normal excited states, multiply excited states and high-n Rydberg levels; the measurements of mean lifetimes above 10-12 s and metastable states up to 100 ns; high-resolution Auger electron measurements; and the application of atomic alignment and orientation by both perpendicular and tilted foils to measurements of atomic structures and analysis of the beam-foil excitation process. A theoretical description of the emission of light from anisotropically excited systems is included. Associated techniques of time-resolved spectroscopy are compared.

https://iopscience.iop.org/article/10.1088/0034-4885/40/2/002/pdf

Beam-foil spectroscopy

Radiation emitted from silicon beams at 35, 38 and 45 MeV excited by passage through thin carbon foils has been studied in the range 3-9 AA using a curved-crystal X-ray spectrometer. More than 100 lines have been observed, of which only one quarter had been observed or predicted from solar or laboratory plasma spectra. Most of the previously unobserved lines may be attributed to satellites of H- and He-like transitions arising in three- and four-electron Si ions. The lifetime of the Si XIII 23P1 state has been measured, and a preliminary experimental value of 6.5+or-1.3 ps obtained.

https://iopscience.iop.org/article/10.1088/0022-3700/12/10/013/pdf

The X-ray spectra of H-like, He-like and Li-like silicon ions after foil excitation

The determination of atomic transition probabilities and lifetimes is an active research area, as may be seen from the following three indicators: (a) the number of research papers since the publication of the first general bibliography(1) in 1962 has grown from 650 to nearly 3000; (b) the data known in 1962 covered roughly 105 spectral lines, a number which has increased by an order of magnitude, to roughly 106; (c) the accuracy of the numerical data has significantly improved and is now, on average, typically in the range from 10% to 25% versus roughly 25%-50% 15 years ago. The numbers show that the improvement in accuracy lags behind the other two advances, and the relatively large uncertainties point to the continuing difficulties in performing accurate determinations, a central subject which will come up many times throughout this chapter. A further indication for the steady growth and development is that several approaches which dominate the field now did not even exist in the early 1960s or had not been developed to a practical state for large-scale production of highquality data.

Atomic Transition Probabilities and Lifetimes

Transition probabilities relate to atomic structure and dynamics in ways that are different from straightforward spectra. Besides being a tool for fundamental physics studies, the knowledge of transition probabilities is essential for applications in plasma physics and astrophysics. Techniques and procedures used for measuring the lifetimes of levels in highly charged ions by employing an electron beam ion trap are reviewed to illustrate the state of the art. Examples are drawn from experiments that involve observations in the visible, extreme-ultraviolet, and X-ray ranges, and cover atomic lifetimes in the femtosecond to second range.PACS Nos.: 32.70.Cs, 32.30.Jc, 32.30.Rj

Atomic lifetime measurements employing an electron beam ion trap

We report a new technique for the measurement of short lifetimes (${10}^{\ensuremath{-}14}$ sec) of innershell vacancies in heavy-ion projectiles moving through thin, solid targets. The technique is applicable whenever the yield of projectile x rays does not increase in proportion to target thickness. Lifetime values of 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ and 3.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ sec have been found for $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ transitions, respectively, in highly stripped sulfur ions.

G. Kalkoffen

Papers

New Technique for the Measurement of Lifetimes of Heavy-Ion Inner-Shell Vacancies

Target-thickness dependence of X-ray yields in heavy ion-atom collisions