Influence of relative humidity in sensing halogenated hydrocarbons with Reflectometric Interference Spectroscopy (RIfS)

For stand-alone sensor systems apart from defined laboratory circumstances sensors are required, which show a high stability against perturbing environmental influences like the relative humidity (r.h.). We present a portable sensor system, which is capable to quantify tetrachloroethene (TCE) in humid air. The system works highly reproducible and shows only negligible cross-sensitivity towards relative humidity. This allows a single calibration valid from 0 to 80% r.h.. Therefore, referencing with an extra sensor for humidity is not necessary. Binary mixtures of TCE and freone R113 were quantified for 0 and 40% r.h. with a root mean square error of prediction of approximately 3% with respect to the maximum concentration of TCE and R113. The sensitive elements used in the experiments consisted of thin polymer films on glass substrates. The measurements were performed with the optical measurement technique RIfS (Reflectometric Interference Spectroscopy). Received: 29 May 1998 / Revised: 4 August 1998 / Accepted: 8 August 1998     

In-beam γ-spectroscopy with relativistic radioactive ion beams

This work demonstrates the feasibility of in-beam %-spectroscopy employing radioactive ion beam species at relativistic energies of E = 210 ~ 280 A · MeV. Neutron-rich nuclei below ⁴⁸Ca with neutron number between the two magic numbers 20 and 28 have been investigated. Using a Pb target, single step inelastic excitation originating mainly from Coulomb interaction takes place populating preferentially low-lying low-spin states and enabling the extraction of B(E2) values. On a C target, nucleon removal reactions are dominating and medium-spin states are populated thus offering spectroscopic information in neighboring nuclei. Cross sections of inelastic excitation are determined and compared to coupled-channels calculations. Two new states of the very neutron-rich nucleus ⁴⁴Ar at 1.78(8) MeV and 2.61(16) MeV are deduced from %-transitions.     

Speciation of butyl- and phenyltin compounds in sediments using pressurized liquid extraction and liquid chromatography-inductively coupled plasma mass spectrometry

A liquid chromatographic method with inductively coupled plasma mass spectrometry is proposed for the speciation of butyl- (monobutyltin, dibutyltin, tributyltin) and phenyl- (monophenyltin, diphenyltin, triphenyltin) tin compounds in sediments. After evaluation of different additives in the mobile phase, the use of 0.075% (w/v) of tropolone and 0.1% (v/v) of triethylamine in a mobile phase of methanol-acetic acid-water (72.5:6:21.5) allowed the best chromatographic separation of the six compounds. Pressurized liquid extraction (PLE) with a methanolic mixture of 0.5 M acetic acid and 0.2% (w/v) of tropolone was suitable for the quantitative extraction of butyl- and phenyltin compounds with recovery values ranging from 72 to 102%. This analytical approach was compared to conventional solvent extraction methods making use of acids and/or organic solvent of medium polarity. The main advantages of PLE over conventional solvent extraction are: (i) the possibility to extract quantitatively DPhT and MPhT from sediments, which could not be done by a solvent extraction approach; (ii) to preserve the structural integrity of the organotin compounds; (iii) to reduce the extraction time from several hours in case of solvent extraction techniques to just 30 min. For spiked sediments, limits of detection ranged from 0.7 to 2 ng/g of tin according to the compound. The relative standard deviations were found to be between 8 and 15%. The developed analytical procedure was validated using a reference material and was applied to various environmental samples.     

Enhanced neutron pair transfer and collective excitations in the system 206Pb + 118Sn at barrier energies

At energies below the Coulomb barrier, neutron transfer and Coulomb excitation have been measured in a very heavy asymmetric nuclear system, in ²⁰⁶Pb + ¹¹⁸Sn. These are semi-magic nuclei showing super-fluid properties. Particle-γ coincidence techniques using 5 Euroball Cluster detectors (EB), combined in a set-up with the Heidelberg-Darmstadt NaI Crystal Ball (CB), have been used. Position-sensitive detectors allowed the observation of scattering processes covering angles from 110 up to 150 degrees. The fragments are identified via the known γ-decays of the lowest excited states using the high resolution of EB. Using the unique feature of the set-up with the CB, transfer to well-defined final channels with known quantum numbers is selected using the high-efficiency multiplicity filter of the CB with no second γ-ray, i.e. without feeding. The data are analysed using the semi-classical approach and transfer probabilities are obtained. Coulomb excitation has been analysed using known transition probabilities. The enhancement is deduced for the two-neutron transfer populating the low-lying super-fluid 2⁺ states in ¹²⁰Sn and ¹¹⁶Sn, while the 2n transition remains in the ground state for the ^20NPb nuclei. Large enhancements up to EF ≃ 10³ are observed. This is the first observation of neutron pair transfer enhancement for a heavy nuclear binary system with super-fluid properties with experimentally separated levels. The calculations with microscopic 2-neutron wave functions, with configuration mixing over six shell model configurations and using the coupled reaction channels approach, reproduce well the observed probabilities and the enhancement. Received: 27 August 2002 / Accepted: 9 December 2002 / Published online: 25 March 2003 RID="a" ID="a"e-mail: oertzen@hmi.de Communicated by D. Schwalm     

Negligible magnetism in excellent structural quality Cr(x)Ti(1-x)O(2) anatase: contrast with high-T(C) ferromagnetism in structurally defective Cr(x)Ti(1-x)O(2)

We reexamine the mechanism of ferromagnetism in doped TiO(2) anatase, using epitaxial Cr:TiO(2) with excellent structural quality as a model system. In contrast to highly oriented but defective Cr:TiO(2) (approximately 0.5 micro(b)/Cr), these structurally superior single crystal films exhibit negligible ferromagnetism. Similar results were obtained for Co:TiO(2). We show for the first time that charge-compensating oxygen vacancies alone, as predicted by F-center mediated exchange, are not sufficient to activate ferromagnetism. Instead, the onset of ferromagnetism correlates with the presence of structural defects.     

Improved limit on the rate of the decay K+ --> pi(+)&mgr;(+)e(-)

We report results of a search for the lepton-family number violating decay K+-->pi(+)&mgr;(+)e(-) from data collected by experiment E865 in 1996 at the Alternating Gradient Synchroton of Brookhaven National Laboratory. We place an upper limit on the branching ratio at 3.9x10(-11) ( 90% C.L.). Together with results based on data collected in 1995 and an earlier experiment, E777, this result establishes a combined 90% confidence level upper limit on the branching ratio at 2.8x10(-11). We also report a new upper limit on the branching ratio for pi(0)-->&mgr;(+)e(-) of 3.8x10(-10) ( 90% C. L.).     

Hydrogenation of ketones and olefins via hydrogen transfer catalyzed by rhodium and iridium phosphine complexes

The reduction of ketones and olefins by hydrogen transfer from isopropanol is catalyzed by tertiary phosphine complexes of rhodium and iridium. The influence of the nature of the ligands and of the reaction conditions on the catalytic activity has been investigated. The reduction of the carbonyl group in the presence of olefins is also reported.