RESUMEN
An experiment was performed at the scientific neutron source FRM II in Garching to determine the cumulative antineutrino spectrum of the fission products of U238. Target foils of natural uranium were irradiated with a thermal and a fast neutron beam and the emitted ß spectra were recorded with a γ-suppressing electron telescope. The obtained ß spectrum of the fission products of U235 was normalized to the data of the magnetic spectrometer BILL. This method strongly reduces systematic errors in the U238 measurement. The ß spectrum of U238 was converted into the corresponding ν¯e spectrum. The final ν¯e spectrum is given in 250 keV bins in the range from 2.875 to 7.625 MeV with an energy-dependent error of 3.5% at 3 MeV, 7.6% at 6 MeV, and â³14% at energies â³7 MeV (68% confidence level). Furthermore, an energy-independent uncertainty of â¼3.3% due to the absolute normalization is added. Compared to the generally used summation calculations, the obtained spectrum reveals a spectral distortion of â¼10% but returns the same value for the mean cross section per fission for the inverse beta decay.
RESUMEN
Density functional theory calculations predict the surface segregation of Cu in the second atomic layer of Pd which has not been unambiguously confirmed by experiment so far. We report measurements on Pd surfaces covered with three and six monolayers of Cu using element selective positron-annihilation-induced Auger electron spectroscopy (PAES) which is sensitive to the topmost atomic layer. Moreover, time-resolved PAES, which was applied for the first time, enables the investigation of the dynamics of surface atoms and hence the observation of the segregation process. The time constant for segregation was experimentally determined to τ=1.38(0.21) h, and the final segregated configuration was found to be consistent with calculations. Time-dependent PAES is demonstrated to be a novel element selective technique applicable for the investigation of, e.g., heterogeneous catalysis, corrosion, or surface alloying.
RESUMEN
The infection with gillworms (Dactylogyrus sp.) causes severe problems in the keeping and breeding of tropical ornamental fishes, e.g. Discus (Symphisodon aequifasciata). Treatment of gillworm disease with different drugs has been shown in the past to be insufficient. Therefore, the effectiveness of a long-term use of praziquantel was evaluated in ornamental fish. Cumulative doses up to 10 mg praziquantel/l water were tolerated without side-effects by Angel Fish (Pterophyllum scalare), Discus, and a variety of catfish species (Ancistrus sp., Corydoras sp.). It was found appropriate to start with a dosage of 2.5 mg/l and to add the same dosage every other day several times. All adult parasites and larvae were killed by this treatment. For the complete elimination of the Dactylogyridae-population in a closed aquarium system, 3 therapy-cycles (duration: 5-6 d, accumulated dosage: 2.5 mg/l/d) prooved to be effective. It was important to interrupt the therapy-cycles with intervals without medication (1 to 4 weeks).