Spectroscopy of Ly-α Lines at Storage Rings by Crystal Spectrometry and Absorption Edge Technique

Crystal spectrometry and absorption edge technique have the capability to overcome the gap in accuracy between experiment and theory in the strong field domain of QED. New results are presented which indicate the capacity of these methods to measure the energies of X-rays emitted by highly charged heavy ions at modern storage rings with a precision sensitive to second order corrections to the Lambshift in H-like very heavy ions. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-resolution wavelength-dispersive spectroscopy of K-shell transitions in hydrogen-like gold

We present a measurement of K-shell transitions in H-like gold (Au⁷⁸⁺) using specially developed transmission type crystal spectrometers combined with Ge(i) microstrip detectors. The experiment has been carried out at the Experimental Storage Ring at GSI in Darmstadt. This is a first high-resolution wavelength-dispersive measurement of a K-shell transition in a high-Z H-like ion, thus representing an important milestone in this field. Ideas on possible future improvements are discussed as well.     

In situ mapping of high-pressure fluids using hydrothermal diamond anvil cells

We present new results combining high pressures and temperatures attainable in a diamond anvil cell with in situ synchrotron radiation induced micro-X-ray fluorescence measurements. Hydrothermal diamond anvil cells experiments have been performed by measuring the partitioning of Pb between aqueous fluids (pure water or NaCl-enriched water) and hydrous silicate melts of haplogranite composition using synchrotron X-ray fluorescence. The in situ measurements were performed in the range 0.3–1.2 GPa and 730–850 ^°C both in the aqueous fluid and in the silicate melts being in equilibrium. Pb is strongly partitioned into high-pressure–temperature hydrous melts when Cl is present in either the hydrous melt or the aqueous fluid. Moreover, our comparisons of in situ results with post-mortem results show that significant changes take place during rapid quenching especially when samples are small (few hundred of microns in diameter). Water exsolution is induced by the quench in the silicate melt showing the high mobility of Pb which immediately partitions into the water vapor phase during the quench. The current in situ approach offers thus a pertinent complementary method to the classical experimental petrology investigations.     

Crystal optics for hard-X-ray spectroscopy of highly charged ions

A twin crystal-spectrometer assembly, operated in the focusing compensated asymmetric Laue geometry has been developed for accurate spectroscopy of fast highly charged heavy ions in the hard-X-ray region. Coupled to the focusing crystal optics is a specially developed two-dimensional position-sensitive X-ray detector which is necessary for retaining spectral resolution also for fast moving sources. We summarize the crystal optics and demonstrate the usefulness of the instrument for spectroscopy of both stationary and fast moving X-ray sources. Results are reported from several tests employing a ¹⁶⁹Yb gamma-ray source and the Lyman radiation of one-electron Pb⁸¹⁺ ions traveling at a velocity corresponding to β ≡ v/c ≈ 0.59. The features of the instrument presented may be useful in many applications where it appears difficult to make the leap from conventional X-ray energy measurements to wavelength-dispersive spectroscopy based on crystal optics.     

Compression behavior of nanocrystalline anatase TiO2

We present a synchrotron X-ray diffraction study of pressure-induced changes in nanocrystalline anatase (with a crystallite size of 30-40 nm) to 35 GPa. The nanoanatase was observed to a pressure above 20 GPa. Direct transformation to the baddeleyite-TiO₂ polymorph was seen at 18 GPa. A fit of the pressure versus volume data to a Birch-Murnaghan equation yielded the following parameters: zero-pressure volume, V₀=136.15 Å³, bulk modulus, K_T=243(3) GPa, and the pressure derivative of bulk modulus, K′=4 (fixed). The bulk modulus value obtained for the nanocrystalline anatase is about 35% larger than that of the macrocrystalline counterpart.