The formation of the $\left[1s2s\right]$ $S$ states in heliumlike uranium $\left({\mathrm{U}}^{90+}\right)$ has been studied in relativistic collisions of initially lithiumlike uranium $\left({\mathrm{U}}^{89+}\right)$ ions with ${\mathrm{N}}_2$ target molecules. By measuring projectile x-ray emission in coincidence with projectile ionization, a strong selectivity for the formation of the $\left[1s2s\right]$ $S$ states in heliumlike uranium is observed. This selectivity is found to be unaffected by the subsequent rearrangement of the atomic orbitals involved. By measuring the photon emission associated with the decay of the $\left[1s2s\right]$ ${}^{1}S_0$ and the $\left[1s2s\right]$ ${}^{3}S_1$ substates, we obtain for their relative population probabilities a ratio of close to 1. This finding deviates considerably from the assumption of a statistical distribution $2J+1$.

LaBr₃:Ce,CeBr₃ and GAGG:Ce scintillators were investigated and the determined characteristics were compared with those obtained for the well-known and widely used CsI:Tl and NaI:Tl crystals. All the detectors were of the same size of 10 × 10 × 5 mm³. The aim of this test study was to single out scintillation detectors most suitable for γ-ray spectrometry and γ-ray emission radial profile measurements in high-temperature plasma experiments. Decay time, energy resolution, non-proportionality and full energy peak detection efficiency ere measured for γ-ray energies up to 1770 keV. Due to their good energy resolution, short decay time and high detection efficiency for MeV gamma rays, LaBr₃:Ce and CeBr₃ scintillators are proposed as the best candidates for use especially under conditions of high count rates, which are expected in the forthcoming DT experiments.

This article presents a detailed analysis of the K$\alpha${} x-ray spectra of Si induced by 11.4~MeV/u Ca projectiles penetrating a low-density SiO2 aerogel target measured with high spectral and spatial resolution at the UNILAC accelerator at GSI-Darmstadt. The low-density material used in the experiment was crucial for the space-resolved studies of the Si x-ray radiation (for different energies of stopping Ca ions). The stopping length of the 11~MeV/u Ca ions reaches up to 10~mm in the low-density SiO2 aerogel, whereas in regular quartz solid targets it is about 100 times shorter. The analysis of the x-ray spectra emitted by the stopping medium has shown a high level of the L-shell ionization, especially in the later considered phase (Ep~5~MeV/u) of the stopping process. It has been further demonstrated that the population of the highly ionized states produced in the ion-atom collisions can be substantially reduced in the time between the collision and the x-ray emission due to the very intense rearrangement processes occurring in Si situated in the chemical environment of oxygen atoms. Moreover, comparison of the experimental values of the K$\alpha${} L-shell satellite energy shifts with the results of the multiconfiguration Dirac-Fock calculations allows us to find that Si valence electron configuration is enriched due to electron transfer from valence-electron-rich oxygen atoms into highly ionized silicon atoms. Our results indicate that the Coulomb explosion in a highly ionized track core is prevented by rapid neutralization in the femtosecond time scale.