微細ガラス破片の非破壊微量元素分析と希少性の定量的評価

Abstract

Micro X-ray fluorescence spectrometry (μXRF) was applied to the non-destructive determination of trace elements in glass fragments. In μXRF, if the thickness of glass sample was not enough, the peak intensities decreased. The influence of this effect on forensic glass discrimination is not clear. In addition, the rarity of glass distributed in Japan has not reported yet. Therefore, in this study, we examined the influence of the peak intensity decrease on forensic glass discrimination and evaluated the rarity by constructing new databases including 921 refractive index (RI) data and 147 elemental peak intensity ratios (elemental ratios, Ca/Mg, Ca/K, Ca/Ti, Ca/Fe, Fe/Zr, Sr/Zr) data. As a result, along with the decrease of the glass sample size, the elemental peak intensity (such as Mg, K, Ca) and the elemental ratios (Ca/Mg, Ca/K) kept almost constant, but the elemental peak intensity (such as Sr, Zr) decreased and the elemental ratios (Fe/Zr, Sr/Zr) changed. The elemental ratios of 1 mm or more particle size were equivalent to those of infinite thickness. On the other hand, even though the elemental ratios of 1 mm or less particle size changed, the elemental ratios could be compared by preparing the samples with the same conditions between them for comparison. The maximum frequency of RI was 10.8 %, and the maximum frequencies of elemental ratios were 34.5 % for Ca/Mg and 26.4 % for Sr/Zr, and the other elemental ratios were widely distributed in the database. The likelihood ratio for RI increased as the number of the match fragments increased, and the likelihood ratio for elemental ratios increased as the number of the discrimination factors increased. Finally, the restrictions on forensic glass discrimination using μXRF were clarified and the rarity of glass distributed in Japan was evaluated quantitatively.