In situ Investigation during Low Pressure Carburizing by Means of Synchrotron X-ray Diffraction*

In situ X-ray diffraction investigations during low pressure carburizing (LPC) processes were performed with a specially developed process chamber at the German Electron Synchrotron Facility (DESY) in Hamburg, Germany. Carbon saturation in austenite was reached in less than 20 seconds for all processes with different parameters and carbides formed at the surface. Therefore, the direct contribution of carbon donor gas to the carbon profile after 20 seconds was reduced to very low levels. After that point, further supply of carbon donor gas increased the amount of carbides formed at the surface, which will contribute to the carbon profile indirectly by dissolution in the following diffusion steps. During quenching, martensite at higher temperatures had a lower c/a ratio than later formed ones. This difference is credited to self-tempering effects and reordering of carbon atoms within the martensite lattice.

Impact of Different Components and Boundary Conditions on the Eigenfrequencies of a Magnet–Girder Assembly

Synchrotron radiation facilities are very important in different areas of fundamental and applied science to investigate structures or processes at small scales. Magnet–girder assemblies play a key role for the performance of such accelerator machines. High structural eigenfrequencies of the magnet–girder assemblies are required to assure a sufficient particle beam stability. The objective of the present parametric study was to numerically investigate and quantify the impact of different boundary conditions and components on the magnet–girder eigenfrequencies. As case studies, two 3 m long girder designs following the specifications of the PETRA IV project at DESY (German Electron Synchrotron, Hamburg, Germany) were selected. High magnet–girder assembly eigenfrequencies were achieved by, e.g., positioning the magnets close to the upper girder surface, increasing the connection stiffness between the magnets and the girder and between the girder and the bases, and positioning the girder support points as high as possible in the shape of a large triangle. Comparing the E/ρ ratio (E: Young’s modulus, ρ: material density) of different materials was used as a first approach to evaluate different materials for application to the girder. Based on the findings, general principles are recommended to be considered in the future girder design development processes.

Reaction of ammonia and dioxygen in solid neon excited with far-ultraviolet radiation investigated with electronic and vibrational spectra

Irradiation of dilute mixtures of NH3 and O2 dispersed in solid Ne at 3.6 K with radiation of wave lengths 200, 192.5, 173 and 143 nm from an electron synchrotron initiated photochemical dissociation of those precursors and the production of N, NH, NH2, O, O3, HO2, NO, NO2, N2O, H2O, HONO in both s-cisoid and s-transoid rotational isomers, and HONO2, detected according to their spectra in mid-infrared absorption from 450 to 4000 cm-1, and in absorption and emission from 200 to 1100 nm. HONO2 was not previously detected in related experiments even though our conditions were much more dilute.

A myriad of melt inclusions: a synchrotron microtomography study of melt inclusions and vapour bubbles from Colli Albani (Italy)

<p>Melt inclusions provide a window into the inner workings of magmatic systems. Both mineral chemistry and volatile distributions within melt inclusions can provide valuable information about the processes modulating magma ascent and preceding volcanic eruptions. Many melt inclusions host vapour bubbles which can be rich in CO<sub>2</sub> and H<sub>2</sub>O and must be taken into consideration when assessing the volatile budget of magmatic reservoirs. These vapour bubbles can be the product of differential volumetric contraction between the melt inclusion and host phase during an eruption or indicate an excess fluid phase in the magma reservoir. Thus, determining the distribution of volatiles between melt and vapour bubbles is integral to our fundamental understanding of melt inclusions, and by extension the evolution of volatiles within magmatic systems.</p><p>A large dataset of 79 high-resolution tomographic scans of clinopyroxene and leucite phenocrysts from the Colli Albani Caldera Complex (Italy) was recently acquired at the German Electron Synchrotron (DESY). These tomograms allow us to quantify the volume of melt inclusions and associated vapour bubble both glassy and microcrystalline melt inclusions. Notably, in the glassy melt inclusions the vapour bubbles exist either as a single large vapour bubble in the middle of the melt inclusion or as several smaller vapour bubbles distributed around the edge of the melt inclusion. These two types of melt inclusions can coexist within a single crystal. We suggest that the occurrence of these rim- bubbles is caused by one of two exsolution pathways, either pre-entrapment and bubble migration or post entrapment with preferential exsolution at the rims. By combining the analysis of hundreds of melt inclusions with the chemistry of the host phase we aim to unveil magma ascent rates and distribution of excess fluids within the magmatic system of Colli Albani, which produced several mafic-alkaline large volume ignimbrites.</p>

A search for new light charged particles in photoproduction

Motivated by recent V.A. Nikitin’s reports on observation of new light charged particles with a 2-meter JINR propane bubble chamber we perform an experiment at the LPI electron synchrotron "Pakhra" with the aim to detect such particles in the Bethe–Heitler process. Theoretical limits for masses of new light charged particles of spin 0, 1/2 and 1 arising from precise data on the muon anomalous magnetic moment are recalculated and updated. A geometry of the photoproduction experiment is proposed that optimizes signal-tonoise ratio. First results of the experiment are exposed.