Determination of90Sr in environmental samples with resonance ionization spectroscopy in collinear geometry

A new, fast technique for trace analysis of the radioactive isotopes⁸⁹Sr and⁹⁰Sr in environmental samples has been developed. Conventional mass separation is combined with resonance ionization spectroscopy in collinear geometry, which provides high selectivity and sensitivity. In addition, a chemical separation procedure for sample preparation has been developed. The described technique was used to determine the⁹⁰Sr content in 870 m³ air samples collected near Munich during and shortly after the Chernobyl reactor accident in April 1986. The content of⁹⁰Sr was measured to be 1.4 mBq per m³, corresponding to 1.6 × 10⁹ atoms of⁹⁰Sr per sample. This value is in good agreement with the results of radiochemical measurements.This publication comprises part of the Dissertations of J. Stenner and K. Zimmer     

Anodic phenyl-onium cation formation: Part II. Reaction mechanism and optimization for the anodic formation of diphenyliodonium cations

The anodic coupling of iodobenzene and benzene to the diphenyliodonium cation is shown to be based on attack of an iodobenzene radical cation on a benzene molecule at the anode surface. Only on platinum anodes in acetonitrile solutions the respective adsorption conditions of benzene and iodobenzene are so favourable that a self coupling to the iodophenylphenyliodonium cation can be avoided. According to the predictions which are based on the electrode kinetic investigations, optimal conditions for the coupling are: (1) low working temperature, (2) low working potential (i.e.c.d. around 18–20 mA cm^?2), (3) high iodobenzene/benzene ratio in the bulk of the solution. Under these conditions 85% current efficiency and 95% mass yield for the coupling are obtained.     

Brennstoffzellentechnik

More than 150 years ago Sir Groe invented the fuel cell. Material problems prohibited this type of gassupplied battery to go to market for a very long time. A break-through was achieved during the last 30 years so that today we can distinguish two low-temperature fuel cell technologies (phosphoric acid and membrane cells) from two high-temperature technologies (molten carbonate and oxide ceramic cells) with a working temperature of 650 and 80 to 900°C, respectively. But today only phosphoric acid fuel cells are offered commeriall as containerized 200-kW cogeneration power plants. Membrane cells are most suitable for electrotraction of aumobiles offering a remarkbly low weight per unit power and working with zero emission. The fuel is, however, a particular problem as hydrogen is not easy to store and too expensive. The ultimate goal is supplying the car with methanol and combusing methanol directly in the fuel cell. However, this aim might be only achieved after several more years of intensive research and development.     

Determination of a three-step excitation and ionization scheme for resonance ionization and ultratrace analysis of Np-237

The long-lived radio isotope ²³⁷Np is generated within the nuclear fuel cycle and represents a major hazard in the final disposal of nuclear waste. Related geochemical research requires sensitive methods for the detection of ultratrace amounts of neptunium in environmental samples. Resonance ionization mass spectrometry (RIMS) has proven to be one of the most sensitive methods for the detection of plutonium. A precondition for the application of RIMS to ultratrace analysis of neptunium is the knowledge of an efficient and selective scheme for optical excitation and ionization. Therefore, a multitude of medium to high-lying atomic levels in neptunium was located by applying in-source resonance ionization spectroscopy. By using excitation via six previously known first excited, intermediate levels of odd parity, a set of twelve so far unknown high-lying levels of even parity were identified and studied further for their suitability in resonant excitation/ionization schemes. Autoionizing resonances for efficient ionization of neptunium atoms were subsequently accessed spectroscopically. Altogether five resonance ionization schemes were investigated and characterized concerning their saturation behavior and relative efficiency. Applying a calibrated sample, an overall efficiency of 0.3% was determined.     

Laser Ion Source Project at IGISOL

The application of laser ionisation is being developed for the IGISOL mass separator facility in Jyväskylä, Finland. The conceived laser ion source will have two independent pulsed laser systems based on all solid-state lasers and dye lasers for maximal coverage of ionisation schemes throughout the periodic table. A laser ion source trap, LIST, method will be pursued for optimal selectivity.     

Event reconstruction with MarlinReco at the International Linear Collider

After an overview of the modular analysis and reconstruction framework Marlin an introduction on the functionality of the Marlin-based reconstruction package MarlinReco is given. This package includes a full set of modules for event reconstruction based on the particle flow approach. The status of the software is reviewed and recent results using this software package for event reconstruction are presented.      

Ultrafine ash aerosols from coal combustion: Characterization and health effects

Ultrafine coal fly-ash particles, defined here as those with diameters less than 0.5 μm, typically comprise less than 1% of the total fly-ash mass. These particles are formed primarily through ash vaporization, nucleation, and coagulation/condensation mechanisms, which lead to compositions notably different compared to other fine or coarse particle fractions formed by fragmentation. Whereas previous studies have focused on health effects of particulate matter with aerodynamic diameters less than 2.5 μm (PM_2.5) (including both vaporization and fragmentation modes), this paper reports results of interdisciplinary research focused on both characterization and health effects of primary ultrafine coal ash aerosols alone. Ultrafine, fine, and coarse ash particles were segregated and collected from a coal burned in a 20 kW laboratory combustor and two additional coals burned in an externally heated drop tube furnace. Extracted samples from both combustors were characterized by transmission electron microscopy (TEM), wavelength dispersive X-ray fluorescence (WD-XRF) spectroscopy, Mossbauer spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. Pulmonary inflammation was characterized by albumin concentrations in mouse lung lavage fluid after instillation of collected particles in saline solutions and a single direct inhalation exposure. Results indicate that coal ultrafine ash sometimes, but not always, contains significant amounts of carbon, probably soot originating from coal tar volatiles, depending on coal type and combustion device. Surprisingly, XAFS results revealed the presence of chromium and thiophenic sulfur in the ultrafine ash particles. Although the single direct inhalation study failed to reveal significant health effects, the instillation results suggested potential lung injury, the severity of which could be correlated with the carbon (soot) content of the ultrafines. Further, this increased toxicity is consistent with theories in which the presence of carbon mediates transition metal (i.e., Fe) complexes, as revealed in this work by TEM and XAFS spectroscopy, promoting reactive oxygen species, oxidation–reduction cycling, and oxidative stress.     

New aspects of diphenylbutadiene photochemistry. Regiospecific hula-twist photoisomerization

In EPA glass at liquid nitrogen temperature, the E,E isomer of diphenylbutadiene (DPB) was photostable, while both the Z,E and Z,Z isomers underwent selective HT isomerization at center 1 giving the stable conformer of the double-bond isomerized trans product. That HT-1 was involved rather than the OBF process was shown by results of o,o'-dimethyl-DPB. Formation of unstable trans product corresponded to simultaneous configurational and conformational isomerization. The regioselectivity was found not sensitive to a substituent effect, as shown by the similar reactivity in p,p'- or o,o'-bistrifluoromethyl-DPB.     

Cover Picture

The cover picture shows the X-ray structure of a squalene-hopene cyclase (ribbon diagram) in the center. Squalene and 2,3-oxidosqualene cyclases catalyze the formation of up to five rings and nine stereocenters in transformations that are both complex and elegant. The triterpenes which are arranged around the structure outline the principal reaction pathways for the enzymatic conversion of oxidosqualene (upper semicircle) and squalene (lower semicircle). Further details about these fascinating reactions are discussed by Schulz, Liu et al. on p. 2812 ff.