基体分离/MC-ICP-MS测定树皮表层235U/238U同位素比率

分别从日本广岛和京都采集了香樟树(Cinnamomum camphora)树皮样品共12份,用X射线能谱仪研究了树皮表层基体元素组成,并用扫描电镜观察了树皮表层微观形貌.将树皮表层样品进行干灰化法处理后,采用DOWEX(R)1-X8型阴离子交换树脂分离基体元素,然后用多接收器电感耦合等离子体质谱仪(MC-ICP-MS)测定了树皮表层235U/238U同位素比率.研究结果表明:树皮表层主要基体元素为Al,Ca,Fe,K,Mg,Si和C,O,S;采用不同浓度硝酸淋洗DOWEX(R) 1-X8型阴离子交换树脂可实现树皮表层痕量U与基体元素的有效分离.与京都树皮表层相比,广岛树皮表层不仅U含量显著偏高(P=0.012),而且部分样品235U/238U同位素比率亦略高于其自然丰度比.

Determination of 235U/238U Isotope Ratios in Camphor Tree Bark Samples by MC-ICP-MS after Separation of Uranium from Matrix Elements

Twelve camphor (cinnamomum camphora) tree bark samples were collected from Hiroshima and Kyoto, and the matrix element composition and morphology of the outer surface of these camphor tree bark samples were studied by EDXS and SEM respectively. After a dry decomposition, DOWEX 1-X8 anion exchange resin was used to separate uranium from matrix elements in these camphor tree bark samples. Finally, 235U/238 U isotope ratios in purified uranium solutions were determined by MC-ICP-MS. It was demonstrated that the outer surface of these camphor tree bark samples is porous and rough, with Al, Ca, Fe, K, Mg, Si, C, O and S as its matrix element composition. Uranium in these camphor tree bark samples can be efficiently separated and quantitatively recovered from the matrix element composition. Compared with those collected from Kyoto, the camphor tree bark samples collected from Hiroshima have significantly higher uranium contents, which may be due to the increased aerosol mass concentration during the city reconstruction. Moreover, the 235 U/23.U isotope ratios in a few camphor tree bark samples collected from Hiroshima are slightly higher than 0.007 25.