Crystal optics for precision x-ray spectroscopy on highly charged ions—conception and proof

Abstract

The experimental investigation of quantum-electrodydamic contributions to the binding energies of inner shells of highly charged heavy ions requires an accurate spectroscopy in the region of hard x-rays suitable at a limited source strength. For this purpose the focusing compensated asymmetric Laue crystal optics has been developed and a twin-spectrometer assembly has been built and commissioned at the experimental storage ring of the GSI Helmholtzzentrum Darmstadt. We characterize the crystal optics and demonstrate the usefulness of the instrumentation for accurate spectroscopy of both stationary and fast moving x-ray sources. The experimental procedures discussed here may also be applied for other spectroscopic studies where a transition from conventional germanium x-ray detectors to crystal spectrometers seems too demanding because of low source intensity.

Studies at the border between nuclear and atomic physics: Weak decays of highly charged ions

“…The electrons are efficiently stripped away from energetic particles while passing through target material [21][22][23]. Fully-ionised and up to 4-electron ions are routinely produced at energies of about 100 − 400 A MeV [24][25][26][27][28][29][30][31][32][33][34][35]. The selection of the atomic charge state is done by optimising the primary projectile energy, target material and its thickness [36].…”

Wavelength-dispersive spectroscopy in the hard x-ray regime of a heavy highly-charged ion: the 1s Lamb shift in hydrogen-like gold

“…The event rate for this line was about 3.5 counts per hour. This low rate is principally due to the low transmission of the spectrometer of 3×10 −8 [36]. In addition to the Lyman-α, also the spatially resolved Lyman-β transitions could be recorded, clearly evidencing the high resolving power of FOCAL.…”

“…Here the minus sign indicates that the measured laboratory frame energy lies below the 169 Yb-γ line energy. Possible model dependencies and details of the line shape have also been addressed [36] by applying various fitting procedures resulting in negligible uncertainties.…”

“…In conclusion we performed a first measurement of the ground state Lamb shift in a heavy H-like ion (Au 78+ ) using a high resolution crystal spectrometer in combination with a fast and dim source of hard x-rays as present at a heavy-ion storage ring. The energy resolution corresponding to about 60 eV FWHM at 63 keV photon energy [36] surpasses the best semiconductor detectors by almost one order of magnitude. The achieved statistical uncertainty of 2.2 eV is groundbreaking for a crystal spectrometer operated in the region of hard x-rays of H-like high-Z ions.…”

“…The Lyman-α 1 transition wavelength is measured by a set of two identical spectrometers operated in the focussing compensated Laue (FOCAL) geometry [35,36]. This type of spectrometer is well suited to find the right compromise between superior spectral resolving power and sufficient detection efficiency in the situation of very limited source strength and the presence of strong Doppler effects.…”