A model for the evaluation of charge-state distributions of fast heavy ions in solid targets is being developed since late eighties in terms of ETACHA code. Time to time it is being updated to deal with more number of electrons and non-perturbative processes. The calculation approach of the recent one, which is formulated for handling the non-perturbative processes better, is different from the earlier ones. However, the experimental results for the projectiles up to 28 electrons can be compared with the predictions from any versions of ETACHA code. Though earlier versions are not meant for the non-perturbative cases, but the detail comparison suggests that predictions from an earlier version is somewhat superior to that of the recent version. However, certain difference up to 4 units of charge found between the earlier version and experimental results on the mean charge states and charge state distributions is attributed to nonradiative electron capture taking place at the exit surface in the influence of wake and dynamic screening effects. This can be a possible mechanism of multiply charge formation in the electrospray ionization of big molecules. Introduction:Charge changing processes of projectile ions traversing solid or gaseous targets has been a subject of interest for more than 70 years [1] for achieving better fundamental understanding and numerous practical applications [2]. The process is highly intricate due to various physical phenomena including ionization, excitation, radiative decay, Auger decay, electron decay, radiative and non-radiative electron capture, etc. Variation of charge state fractions (CSF) versus charge state called charge state distribution (CSD) is used in both experiments and theories to understand the charge changing processes in detail. Several extensive reviews can be found in the literature [[3][4][5][6] [7]]. These reviews provide the theoretical background and experimental techniques as well as data collected until the date of the corresponding publications on the CSD. The CSDs are normally measured by the standard electromagnetic measurements [4] and in order to understand the measured mean equilibrium charge state data, many semi-empirical formulas such as Thomas-Fermi Model, Bohr Model, Betz Model, Nikolaev-Dmitriev Model, To-Drouin Model, Shima-Ishihara-Mikumo Model, Itoh Model, Ziegler-Biersack-Littmark Model, Schiwietz Model have been developed [8] in tune with the experimental results from electromagnetic measurements. However, the semi-empirical formulas fail to estimate the non-equilibrium charge states and equilibrium foil thickness. Hence, a dedicated effort has been put in developing a model [9].The model calculation of projectile charge-state distributions as a function of penetration depth x in a solid target is performed by solving a set of differential equations to account for different cross sections responsible for corresponding atomic processes such as ionization, excitation, radiative and non-radiative electron capture. Subsequently, numerical calculatio...
We have constructed empirical formulae for fusion and interaction barrier heights using experimental values available in the literature. Fusion excitation function measurements are used for the former and back angle quasi-elastic excitation function for the latter case. The fusion barriers so obtained have been compared with various model predictions such as Bass potential, Christenson and Winther, Broglia and Winther, Aage Winther, Siwek-Wilczyńska and J.Wilczyński, Skyrme energy density function model, and the Sao Paulo optical potential along with experimental results. The comparison allows us to find the best model, which is found to be the Broglia and Winther model. Further, to examine its predictability, the Broglia and Winther model parameters are used to obtain total fusion cross sections showing good agreement with the experimental values for beam energies above the fusion barriers. Thus, this model can be useful for planning any experiments, especially ones aiming for super heavy elements. Similarly, current interaction barrier heights have also been compared with the Bass potential model predictions. It shows that the present model calculations are much lower than the Bass potential model predictions. We believe the current interaction barrier model prediction will be a good starting point for future quasi-elastic scattering experiments. Whereas both the Broglia and Winther model and our interaction barrier model will have practical implications in carrying out physics research near the Coulomb barrier energies.
We have investigated the effect of the target atomic number Z2 on the mean charge state (q¯ using various model predictions such as the Shima–Ishihara –Mikumo, Ziegler–Biersack–Littmark, Schiwietz, Schiwietz–Grande , Fermi-gas-models and theoretical codes with experimental data available in the literature. This investigation makes it possible to determine the best-fit model to calculate q¯. In this work, we discuss the post-collision charge state distribution in different targets used as thin films and projectile beams (Fq+, Siq+, Clq+, and Cuq+) with different charge states (available in literature). A detailed overview of such collision experiments has been explored over a wide energy range of 1.07–3.93 MeV/u. In this contribution, an overview of the mean charge state dependence on the Fermi velocity of target materials is provided. Finally, the influence of the non-radiative electron capture at the target exit surface on the projectile charge state distribution for fast projectiles in different targets is shown, and a comparison is made with experimental data.
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