Tetrahedra packings — Observation of magic numbers for clusters from antimony-tetramers

Sb_n-clusters have been generated by condensation of tetramer units in LN₂-cooled He-gas. Electronic time-of-flight spectra show resolved mass peaks of clusters from tetramers up to n = 240 with pronounced size dependent structure. The observed magic numbers $\text{n}{}^1\text{= 8, 36, 52}\text{and}\text{84}$ are explained by a tetrahedra packing model.     

The velocity distribution of clusters generated by inert gas condensation

The velocity distribution of sodium chloride clusters produced by inert gas condensation is determined by means of a mechanical chopping technique. It is found to be the same for all cluster sizes between 1 and more than 200 molecular units per cluster, ruling out the possibility of cluster mass separation by velocity filters. This is explained by an adiabatic expansion occuring during the cluster's exit from the condensation chamber into the high vacuum of the mass spectrometer.     

Structural defect recovery in GaP after heavy ion implantation

The channeling and blocking effect of electrons and positrons emitted in nuclear decay allows the lattice site location of radioactive impurities implanted into single crystals at small concentrations (ppm) and low implantation fluences (10¹²/cm²). We applied this emission channeling technique to the localization of ^112mIn and ^111mCd after implantation into si-GaP single crystals at different temperatures. After implantation at low temperature and subsequent annealing an increase of the fraction of substitutional probe atoms and a recovery of the local lattice structure between 300 and 500 K were observed. GaP tends to anneal at higher temperatures than GaAs (200–350 K), but compared to GaAs the channeling effects observed in GaP are more pronounced, indicating a more complete recovery of implantation defects.     

Electron irradiation effects on muonium states in silicon

Normal and anomalous muonium were studied in electron irradiated silicon. We found that the two muonium states behave very differently: For normal muonium, the relaxation rate increases if the sample is irradiated whereas it decreases for anomalous muonium. Possible explanations for these processes are discussed.     

Speciation of Se, Fe and Zn in Human Milk Whey: The use of Instrumental Neutron Activation Analysis (INAA) to corroborate element profiles measured with Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)

In human milk trace elements normally exist in a form which can easily be absorbed by the newborn infant. For investigations of the bioavailability of trace elements it is necessary to carry out a speciation analysis of the elements of interest. An independent analytical method has been used for the quality control of the shape of the element profiles obtained from the speciation analysis of Se, Fe and Zn in individual samples to human milk whey after chromatographic separation. For the element detection in the untreated milk fractions Instrumental Neutron Activation Analysis (INAA) was chosen as the reference method. Element distribution patterns have been obtained with Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) using on-line digestion of the fraction, reduction and hydride formation of Se (T-mode). Prior results are compared with those obtained by means of element detection in the untreated fractions (U-mode) with ICP-AES. The elution profiles of Se, Fe and Zn in human milk whey obtained by means of ICP-AES detection using the T-mode show good agreement with the distribution patterns obtained with INAA. Recoveries of 103% for Fe, 86% for Zn and 87% for Se were obtained. The element distribution patterns of Fe and Zn obtained with ICP-AES speciation using the T-mode also show good agreement with those obtained by means of ICP-AES using the U-mode.Dedicated to Professor Dr. Peter Brätter on the occasion of his 60th birthday.