Detlev Degering

Radiometric dating of the type-site for Homo heidelbergensis at Mauer, Germany

The Mauer mandible, holotype of Homo heidelbergensis, was found in 1907 in fluvial sands deposited by the Neckar River 10 km southeast of Heidelberg, Germany. The fossil is an important key to understanding early human occupation of Europe north of the Alps. Given the associated mammal fauna and the geological context, the find layer has been placed in the early Middle Pleistocene, but confirmatory chronometric evidence has hitherto been missing. Here we show that two independent techniques, the combined electron spin resonance/U-series method used with mammal teeth and infrared radiofluorescence applied to sand grains, date the type-site of Homo heidelbergensis at Mauer to 609 ± 40 ka. This result demonstrates that the mandible is the oldest hominin fossil reported to date from central and northern Europe and raises questions concerning the phyletic relationship of Homo heidelbergensis to more ancient populations documented from southern Europe and in Africa. We address the paleoanthropological significance of the Mauer jaw in light of this dating evidence.

Ferromagnetic Semiconductors Studied by Hyperfine Interaction of Nuclear Probes

The ferromagnetic spinels CdCr2Se4 and CuCr2Se4 were investigated by PAC (perturbed angular correlations) after implantation of the probes 111In(111Cd), 111mCd, 111Ag(111Cd) and 77Br(77Se). The site occupation of different probes was determined by magnetic and electric hyperfine interactions. Theoretical calculations of hyperfine parameters by the WIEN97 code gave satisfactory efg (electric field gradients) but the magnetic hyperfine fields are inconsistent with the experiments.

SEMICONDUCTORS WITH STRUCTURALLY DETERMINED VACANCIES : PAC STUDIES

Ternary semiconductors of type □AIIB2IIIC4VI with an ordered array of vacancies were investigated by PAC. Thereby the six probes 111Cd, 117Cd(117In), 111In(111Cd), 111Ag(111Cd), 77Br(77Se) and 77Kr(77Br) were applied. The positions of the different probes are determined and the corresponding electric field gradients by the WIEN 95 code calculated. By 111Ag(111Cd)-probes the vacancies could be substituted. The electronic charge density distributions are discussed. At elevated temperatures the substances show order–disorder transitions. As compared to the X-ray diffraction patterns the beginning of disorder is observed by PAC at distinctly lower temperatures.

Monitoring of natural radionuclides in soils as a tool for precision farming - methodical aspects

The use of natural radionuclide contents for the evaluation of soil quality data was tested by field logs and additional laboratory analyses on vertical profiles. The latter proved a well mixing of soil material in the uppermost 30 cm by ploughing. A mathematical procedure for the consideration of soil moisture and the determination of the “information depth” is presented and lead to good agreement between field and laboratory data.

Quadrupole Interaction in Ternary Chalcopyrite Semiconductors: Experiments and Theory

Electric field gradients have been measured at substitutional lattice sites in ternary semiconductors using Perturbed γ -γ Angular Correlation spectroscopy (PAC). The experimental results for AIBIIIC2 chalcopyrite structure compounds and • AIIB2IIIC4IV defect chalcopyrites are compared with ab nitio calculations. The latter were carried out with the WIEN code that uses the Full Potential Linearized Augmented Plane Wave method within a density functional theory. The agreement between experiment and theory is in most cases very good. Furthermore, the anion displacements in AgGaX2 -compounds (X: S, Se, Te) have been determined theoretically by determining the minimum of the total energy of the electrons in an elementary cell.

Local Probes in Magnetic Semiconductors – PAC Investigations

Magnetic and electric hyperfine interactions in the magnetic semiconductor CdCr2Se4 are measured using 111mCd and 111In(111Cd) PAC. The radioactive probes were implanted. In-probes occupy predominantly the Cr-site, but a part of them is also substituted at the Cd-site. This is proved by the measured internal fields. Theoretical hyperfine fields are calculated by the WIEN97-code.

TDPAC STUDIES ON THE SORPTION OF HF(IV) ONTO A SILICA SURFACE

Abstract181Hf-PAC investigations were undertaken as a contribution to the understanding of the aquatic chemistry of the tetravalent elements. In solution, the growth of polymeric species with increasing pH was observed by PAC. For the sorption of Hf on silica surfaces we found a strong dependence of the PAC results on the pH value. The corresponding sites were assigned to surface complexation and surface precipitation, respectively.