Hypersatellite x-ray decay of $3d$ hollow-$K$-shell atoms produced by heavy-ion impact

We report on the radiative decay of double $K$-shell vacancy states produced in solid Ca, V, Fe, and Cu targets by impact with about 10 MeV/amu C and Ne ions. The resulting $K$ hypersatellite x-ray emission spectra were measured by means of high-energy-resolution spectroscopy using a von Hamos bent crystal spectrometer. The experiment was carried out at the Philips variable energy cyclotron of the Paul Scherrer Institute. From the fits of the x-ray spectra the energies, line widths, and relative intensities of the hypersatellite x-ray lines could be determined. The fitted intensities were corrected to account for the energy-dependent solid angle of the spectrometer, effective source size, target self-absorption, crystal reflectivity, and detector efficiency. The single-to-double $K$-shell ionization cross-section ratios were deduced from the corrected relative intensities of the hypersatellites and compared to theoretical predictions from the semiclassical approximation model using hydrogenlike and Dirac-Hartree-Fock wave functions and from classical trajectory Monte Carlo calculations.

Figure 1

C beam intensity profile employed to correct the $K\alpha$ x-ray spectrum of Ca shown in Fig. 2. The red and blue vertical stripes represent the target areas seen by the pixels' columns 1 and 1024 for the CCD positions 1 (3650–3750 eV) and 9 (4350–4450 eV).

Figure 2

Reconstructed $K$ x-ray spectrum of Ca produced by impact with 143 MeV C ions. In the top panel, the full spectrum is represented within the same logarithmic intensity scale. For the assignments of the different peaks, see text. The energy region corresponding to the weak $K{\beta }^h$ spectrum is shown with an enlarged intensity scale in the inset. The partial spectra corresponding to the different CCD positions needed to cover the whole energy range are plotted in the bottom panel. In this case the intensity scale is linear but the intensities of the regions corresponding to the $K\alpha$ and $K\beta$ diagram lines were multiplied by 0.04 and 0.4, respectively, and offsets in the intensity scale were employed for the different regions to better show the overlapping regions.

Figure 3

Fit of the C-induced $K\alpha$ hypersatellite spectrum of Ca. The top part of the figure shows the measured spectrum (open circles), the linear background (dashed black line), and the total fit (black curve). The fitted components are depicted in the lower part where the red solid line represents the $K{\alpha }_2^h$ hypersatellite, the blue solid lines the first- and second-order $L$ satellites of the $K{\alpha }_{1,2}^h$ hypersatellites, and the red and blue dotted lines the $M$ satellites accompanying the above-mentioned transitions. The fitted $K{\alpha }_1^h$ hypersatellite is too weak to be seen.

Figure 4

Same as Fig. 3 but for the Ne-induced spectrum. The pink solid line (around 4015 eV) corresponds to the $K\beta$ diagram line and the pink dotted lines to the $K\beta M^{-n}$ ($n=1,...,4$) satellites.