Investigation of Dose Rates Exterior to an Above-Ground Waste Storage Facility Using Radiation Transport Models.

The dose rate profile at different heights above the ground and as a function of distance from the north, west, and south walls of an above-ground waste storage facility was analyzed using the Monte Carlo n-Particle Transport eXtended (MCNPX) radiation transport code. The waste storage facility houses 9,996 waste barrels of conditioned waste. The facility has concrete shielding added to the building walls on the north, west, and east sides, with no such additional shielding towards the roof or the south side wall; instead, the distance from the first row of barrels to the wall is extended to allow for maneuverability of a crane on the south side. The dose rate is computed as a function of distance using MCNPX and assuming a homogeneous Co distribution in each waste barrel. Different dose regions are identified and analyzed based on graphical features and best-fit functions. The dose rates were expected to be largest at the wall of the facility and subsequently decrease continuously with distance from the repository; however, our analysis indicates a peak in dose rate observed for all heights on the north and west sides of the facility. This peak is likely due to scattering in the shielding material and atmosphere, and possibly could be ascribed to skyshine. The difference between the dose rate at 1 m outside the wall and the peak dose rate is significant, and indicates that the dose rate measured close to the wall may not always be conservative for extended sources, such as an above-ground waste storage facility.

Assessment of chemical species of lead accumulated in tidemarks of human articular cartilage by X-ray absorption near-edge structure analysis.

A highly specific accumulation of the toxic element lead was recently measured in the transition zone between non-calcified and calcified normal human articular cartilage. This transition zone, the so-called `tidemark', is considered to be an active calcification front of great clinical importance. However, little is known about the mechanisms of accumulation and the chemical form of Pb in calcified cartilage and bone. Using spatially resolved X-ray absorption near-edge structure analysis (µ-XANES) at the Pb L(3)-edge, the chemical state of Pb in the osteochondral region was investigated. The feasibility of the µ-XANES set-up at the SUL-X beamline (ANKA synchrotron light source) was tested and confirmed by comparing XANES spectra of bulk Pb-reference compounds recorded at both the XAS and the SUL-X beamline at ANKA. The µ-XANES set-up was then used to investigate the tidemark region of human bone (two patella samples and one femoral head sample). The spectra recorded at the tidemark and at the trabecular bone were found to be highly correlated with the spectra of synthetic Pb-doped carbonated hydroxyapatite, suggesting that in both of these very different tissues Pb is incorporated into the hydroxyapatite structure.

Improved micro x-ray fluorescence spectrometer for light element analysis.

Since most available micro x-ray fluorescence (micro-XRF) spectrometers operate in air, which does not allow the analysis of low-Z elements (Z or = 6). It offers improved excitation and detection conditions necessary for light element analysis. To eliminate absorption of the exciting and fluorescent radiation, the system operates under vacuum condition. Sample mapping is automated and controlled by specialized computer software developed for this spectrometer. Several different samples were measured to test and characterize the spectrometer. The spot size has been determined by scans across a 10 microm Cu wire which resulted in a full width at half maximum of 31 microm for Mo Kalpha line (17.44 keV) and 44 microm effective beam size for the Cu K edge and 71 microm effective beam size for the Cu L edge. Lower limits of detection in the picogram range for each spot (or microg/cm(2)) were obtained by measuring various thin metal foils under different conditions. Furthermore, detection limits in the parts per million range were found measuring NIST621 standard reference material. Area scans of a microscopic laser print and NaF droplet were performed to show mapping capabilities.

Bone material quality in transiliac bone biopsies of postmenopausal osteoporotic women after 3 years of strontium ranelate treatment.

Strontium ranelate (SrR) is a relatively new treatment for osteoporosis. In this study we investigated its potential impact on human bone material quality in transiliac bone biopsies from postmenopausal osteoporotic women treated 3 years with calcium and vitamin D plus either 2 g SrR per day or placebo. Bone mineralization density distribution (BMDD), strontium (Sr) concentration, collagen cross-link ratio, and indentation modulus were analyzed by quantitative backscattered electron imaging, electron-induced X-ray fluorescence analysis, synchrotron radiation induced micro X-ray fluorescence elemental mapping, Fourier transform infrared imaging, and nanoindentation, respectively. The BMDD of SrR-treated patients was shifted to higher atomic numbers (Z(mean) +1.5%, p < .05 versus placebo). We observed Sr being preferentially incorporated in bone packets formed during SrR treatment up to 6% atom fraction [Sr/(Sr + Ca)] depending on the SrR serum levels of the individuals (correlation r = 0.84, p = .018). Collagen cross-link ratio was preserved in SR-treated bone. The indentation modulus was significantly decreased in younger versus older bone packets for both placebo- (-20.5%, p < .0001) and SrR-treated individuals (-24.3%, p < .001), whereas no differences were found between the treatment groups. In conclusion, our findings indicate that after SrR treatment, Sr is heterogeneously distributed in bone and preferentially present in bone packets formed during treatment. The effect of SrR on BMDD seems to be due mainly to the uptake of Sr and not to changes in bone calcium content. Taken together, these data provide evidence that the investigated bone quality determinants at tissue level were preserved in postmenopausal osteoporotic women after 3-year treatment with 2 g SrR per day plus calcium and vitamin D.