Die Vanadin-Koordination in den Phasen 4 PbO · V2O5 und 8 PbO · V2O5

Coordination of Vanadium in the Phases 4 PbO · V₂O₅ and 8 PbO · V₂O₅ It is demonstrated, using infrared spectroscopy, that the coordination of vanadium in the two binary phases 4 PbO · V₂O₅ and 8 PbO · V₂O₅ is tetrahedral. The spectra in the V? O stretching region closely resembles that of the lead(II) orthovanadate, Pb₃(VO₄)₂.     

Hyperfine interactions in ZrO2–5 wt.% Al2O3 ceramics

Two powder samples of ZrO₂-5 wt.% Al₂O₃ derived from precursor solutions of different pH – 2 for sample (C) and 4 for sample (D) – were prepared by the precipitation method. They were studied using PAC between RT and 1150oC and XRD after heating at increasing temperatures. According to XRD, the addition of Al₂O₃ causes the complete stabilization of tetragonal zirconia in both samples. At a nanoscopic level, however, they present different interactions and thermal evolutions. Sample (C) exhibits predominantly the t₁- and dynamic t₂-forms already reported for pure and yttria-doped stabilized tetragonal zirconias. On the other hand, sample (D) exhibits a novel nanoconfiguration depicted by a totally asymmetric and dynamic EFG whose population achieves 86% at 1150oC and which has been associated to aluminium solubility in zirconia. Upon cooling gradually to RT from the highest temperature, (C) transforms completely to m-ZrO₂ and (D) remains 65% in the metastable tetragonal phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Extractive scintillators for alpha liquid scintillation counting: Anomalies in quenching evaluation

Two important effects in quenching evaluation when using some commercial extractive scintillators in alpha liquid scintillation counting are described. One affects the system quenching value but not the efficiency, while the other modifies the efficiency with no important change in the quenching. For these cocktails, alternative procedures for efficiency evaluation must be chosen. We propose an inner standard procedure which gave adequate results in the application to different kinds of samples.     

Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external ²²Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled or β cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by ²²Na. These powders showed a long lifetime component of 7–8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200°C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from cages only. The beam experiments revealed a high fraction of 3-gamma annihilations in the pressed powder and thin film samples, indicating the annihilation of o-Ps and thereby the existence of large open volumes.     

Observation of a narrow charm-strange meson D(+)(sJ)(2632)-->D(+)(s)eta and D(0)K(+)

We report the first observation of a charm-strange meson D(+)(sJ)(2632) at a mass of 2632.5+/-1.7 MeV/c(2) in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D(+)(s)eta and D0K+. In the D(+)(s)eta decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4+/-3.3 MeV/c(2). There is a corresponding peak of 21 events over a background of 6.9 at 2631.5+/-2.0 MeV/c(2) in the decay mode D0K+. The decay width of this state is <17 MeV/c(2) at 90% confidence level. The relative branching ratio Gamma(D0K+)/Gamma(D(+)(s)eta) is 0.14+/-0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D(+)(s)eta decay mode.     

Observation of the decay xi0 --> sigma+ mu- nu(mu)

The xi0 muon semileptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the xi0 beta decay mode and yields a value for the ratio of decay rates gamma(xi0 --> sigma+ mu- nu(mu))/gamma(xi0 --> sigma+ e- nu(e)) of [1.8(-0.5)(+0.7)(stat) +/- 0.2(syst)] x 10(-2). This is in agreement with the SU(3) flavor symmetric quark model.