Development of Heavy Mineral and Heavy Element Database of Sediments in Japan for Forensic Investigation Using Synchrotron Radiation X-ray Analyses

We have started to construct a nationwide forensic soil sediment database for Japan, based on the heavy mineral and trace heavy element compositions of stream sediments collected at 3024 points across Japan. Each sample was measured by high-resolution synchrotron radiation X-ray powder diffraction (SR-XRD) analysis and high-energy SR X-ray fluorescence analysis (XRF) at SPring-8, the SR radiation facility in Japan. The automated sampling systems allow us to measure 130 powder diffraction patterns and 130 XRF spectra per day, respectively using the sediment samples of only a few milligrams, which enabled us to construct a database of a large number of samples. The concentrations of heavy elements such as rare earth elements, Cs and W in soil sediments can be determined by the calibration curve method by using high-energy SR-XRF utilizing monochromatic X-rays of 116 keV. A heavy element concentration map superimposed on a geographical map of Japan was successfully prepared from these analytical data. The heavy mineral compositions were semi-quantitatively evaluated by using the peak intensity of the characteristic XRD peaks of the component minerals measured by a Debye-Scherrer camera having a radius of 286.5 mm, recorded with an imaging plate and monochromatic X-rays (lambda = 1.0 angstrom). This study demonstrates that these XRF and XRD data collected from sediments of Chiba, Kofu, Shizuoka and Shikoku region well reflect the geological and geographical signature of the sediment samples, which can be used for a provenance estimation of soil evidence from a crime scene.