Stephan Puchegger

14C dating with the bomb peak: An application to forensic medicine

Abstract Samples originating from the time period after 1950 can be radiocarbon dated utilising the 14C bomb peak as a calibration curve. The applicability of “radiocarbon dating” of recent organic human material for the determination of the time of death of humans was tested. The radiocarbon results from hair and lipid samples from individuals with known date of death were compared with the results from two individuals with unknown time of death. An estimate of the year of death for the unknowns could be derived by this way. Due to the long turnover time of collagen in human bones it is not possible to use the radiocarbon content of bone collagen for a reliable estimate. In order to study the time dependence of the collagen turnover we tested “soft” chemical methods for the isolation of collagen from the bone matrix. First radiocarbon results of this investigation are presented.

Extension of the measuring capabilities at VERA

Our standard setup used for accelerator mass spectrometry (AMS) with 14C was modified for measuring various other radionuclides. The injection and detection systems were modified to suit the particular isotope investigated. 10B, the stable isobar of 10Be, is stopped in a gas absorber in front of a surface barrier detector. 26Al is measured similar to 14C, except for a modification of the timing for the sequential isotope injection. For 129I, a time-of-flight setup was built to separate 129I from 127I. For heavier rare radionuclides, the mass resolution of the injector system was improved. We also improved our capabilities in measuring carbon samples having very low mass. We describe two different methods to prepare and to measure sub-milligram 14C samples.

Keratin homogeneity in the tail feathers of Pavo cristatus and Pavo cristatus mut. alba

The keratin structure in the cortex of peacocks’ feathers is studied by X-ray diffraction along the feather, from the calamus to the tip. It changes considerably over the first 5 cm close to the calamus and remains constant for about 1 m along the length of the feather. Close to the tip, the structure loses its high degree of order. We attribute the X-ray patterns to a shrinkage of a cylindrical arrangement of β-sheets, which is not fully formed initially. In the final structure, the crystalline beta-cores are fixed by the rest of the keratin molecule. The hydrophobic residues of the beta-core are locked into a zip-like arrangement. Structurally there is no difference between the blue and the white bird.

Non-contacting strain measurements of ceramic and carbon single fibres by using the laser-speckle method

A non-contacting laser correlation sensor is used to determine the strain of different ceramic (alumina, silicon carbide) and carbon fibres in a single fibre tension test. The diameter of these fibres varies from 15 to only 5 mm, which makes the application of conventional strain sensors impossible. The advantage of the non-contacting method is that the strain is directly measured and end-effects from the gripping system need not to be considered. Results for different ceramic and carbon fibres with linear and non-linear stress ‐strain curves are presented as an example. q 2003 Elsevier Ltd. All rights reserved.

Methodological aspects of atmospheric 14CO measurements with AMS

Abstract This paper examines special features arising in the measurement of atmospheric 14 C monoxide. A detailed error analysis of the 14 CO method including sampling, chemical processing and AMS measurement of samples, standards and blanks is given. Problems regarding the term “percent Modern Carbon (pMC)” are discussed, and the conversion of pMC values to atmospheric 14 CO concentrations is explained.

Hutchinson's shear coefficient for anisotropic beams

Timoshenkos theory of vibrating beams requires a shear correction factor to correctly take into account the effects of shear deformation for different beam cross-sections. This correction is crucial for a precise determination of the shear modulus from the resonant frequencies. Hutchinsons beam theory is used to derive a new shear correction coefficient for anisotropic materials. A comparison is made with other shear coefficients for anisotropic materials published in the literature. Computer-simulated spectra are used to validate the new anisotropic shear correction coefficient.

Automated evaluation of 14C AMS measurements

Abstract The huge amount of raw data collected during routine 14 C AMS measurements requires sophisticated processing tools to guarantee the quality and reliability of the resulting radiocarbon dates. This paper discusses the automatic evaluation system, that is in use and under continuous development at the Vienna Environmental Research Accelerator (VERA) laboratory. It includes a calibration program which is able to handle the bomb-peak. The flexibility of the system allows its use for other rare isotopes also.

A detailed 2-year record of atmospheric 14CO in the temperate northern hemisphere

Abstract This paper presents a 2-year record (from September 1996 to July 1998) of atmospheric 14 CO measurements on whole air samples taken at the Mt. Sonnblick observatory (3106 m), a remote high-altitude site in Central Europe. An overall measurement precision of ca. 1/4 molecule 14 CO per cm 3 air has been achieved. A few events including unexpectedly low CO and 14 CO values in winter 1996/97 will be discussed in some detail incorporating stable isotope information. Since the amount of 14 CO data available for the Northern Hemisphere (NH) is rather sparse, this most detailed long-term 14 CO record for NH temperate latitudes may be a valuable contribution to the assessment of global atmospheric OH concentrations.

Mapping dynamical mechanical properties of osteonal bone by scanning acoustic microscopy in time-of-flight mode.

An important determinant of mechanical properties of bone is Youngs modulus and its variation in individual osteons of cortical bone tissue. Its mechanical behavior also depends on deformation rate owing to its visco- or poroelastic properties. We developed a method to measure dynamical mechanical properties of bulk bone tissue at osteonal level based on scanning acoustic microscopy (SAM) using time-of-flight (TOF) measurements in combination with quantitative backscattered electron imaging (qBEI). SAM-TOF yields local sound velocities and qBEI corresponding material densities together providing elastic properties. Osteons (n=55) were measured in three human femoral diaphyseal ground bone sections (∼ 30 µm in thickness). In addition, subchondral bone and mineralized articular cartilage were investigated. The mean mineral contents, the mean sound velocities, and the mean elastic modulus of the osteons ranged from 20 to 26 wt%, from 3,819 to 5,260 m/s, and from 21 to 44 GPa, respectively. There was a strong positive correlation between material density and sound velocity (Pearsons r=0.701; p<0.0001) of the osteons. Sound velocities between cartilage and bone was similar, though material density was higher in cartilage (+4.46%, p<0.0001). These results demonstrate the power of SAM-TOF to estimate dynamic mechanical properties of the bone materials at the osteonal level.

Developments towards a fully automated AMS system

Abstract The possibilities of computer-assisted and automated accelerator mass spectrometry (AMS) measurements were explored. The goal of these efforts is to develop fully automated procedures for “routine” measurements at the Vienna Environmental Research Accelerator (VERA), a dedicated 3-MV Pelletron tandem AMS facility. As a new tool for automatic tuning of the ion optics we developed a multi-dimensional optimization algorithm robust to noise, which was applied for 14C and 10Be. The actual isotope ratio measurements are performed in a fully automated fashion and do not require the presence of an operator. Incoming data are evaluated online and the results can be accessed via Internet. The system was used for 14C, 10Be, 26Al and 129I measurements.