To understand the dynamics of accident-derived radioactive cesium (137Cs) in stem wood that had a substantial amount of heartwood at the time of the Fukushima Dai-ichi Nuclear Power Plant accident, the radial and vertical distributions of 137Cs activity concentration in stem wood of Japanese cedar (Cryptomeria japonica), cypress (Chamaecyparis obtusa), and larch (Larix kaempferi) were investigated. In addition, the natural distribution of stable cesium (133Cs), rubidium (85Rb), and potassium (39K) concentrations was analyzed to determine the characteristics of 137Cs distribution. Wood disks were collected from the tree stems of six cedars, three cypresses, and two larches at multiple heights in 2014, and the concentrations were measured every 2 cm in the radial direction. 137Cs distribution in stem wood differed among tree species, sampling site, and vertical position of the stem within a tree. Statistical analyses suggested that the radial distribution of 137Cs within the heartwood can be explained by the heartwood moisture content and the distance from the treetop, regardless of species, while the distribution between sapwood and heartwood was dependent on the heartwood cross-sectional area and was additionally different between larch and other species. Similarly, the heartwood/sapwood concentration ratios of stable alkali metals differed between larch and the other species. In the larch, the ratio was ca. 0.5 for all elements, but the ratio was over 1.0 and differed among elements in the other species. Consequently, the species-specific difference in the distribution of 137Cs between sapwood and heartwood was considered to be due to different activity levels of radial transport toward the heartwood. The radial variation pattern of the 137Cs/133Cs concentration ratio showed that less 137Cs was transferred to the inner heartwood compared with the 133Cs distribution pattern in many trees; however, there was also a tree in which 137Cs was excessively transferred to the inner heartwood compared with the 133Cs distribution pattern. Such patterns may result from a combination of significant foliar uptake of 137Cs and poor root uptake after the accident, in addition to the high moisture content of the heartwood.

中文翻译：

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福岛第一核电站事故发生3年后，在三种日本针叶树种的茎木中追踪放射性铯

为了了解福岛第一核电站事故发生时心材含量高的茎干中事故源放射性铯（137Cs）的动态，我们对137Cs活性浓度在干柴中的径向和垂直分布进行了研究。研究了日本雪松（Cryptomeria japonica），柏树（Chamaecyparis obtusa）和落叶松（Larix kaempferi）。此外，分析了稳定铯（133Cs），id（85Rb）和钾（39K）浓度的自然分布，以确定137Cs分布的特征。2014年，从六个高大的柏木，三个柏树和两个落叶松的树茎上收集了木片，并在径向每2 cm测量一次浓度。不同树种，采样地点，和树中茎的垂直位置。统计分析表明，心材中137 Cs的径向分布可以用心材含水量和距树顶的距离来解释，而与树种的距离无关，而边材和心材之间的分布取决于心材的横截面积，此外落叶松和其他物种之间的差异。同样，落叶松和其他物种之间稳定碱金属的心材/边材浓度比也有所不同。在落叶松中，该比率为ca。所有元素为0.5，但比率超过1.0，并且在其他物种中元素之间也有所不同。所以，边材和心材之间137 Cs分布的物种特异性差异被认为是由于向心材径向传输的活性水平不同。137Cs / 133Cs浓度比的径向变化规律表明，与许多树木中的133Cs分布规律相比，转移到内心心材的137Cs更少；但是，与133Cs的分布模式相比，还有一棵树将137Cs过度转移到内部心材上。除了心材的高水分含量外，这种模式的产生还可能是由于事故后137Cs的大量叶吸收和根系吸收不良所致。137Cs / 133Cs浓度比的径向变化规律表明，与许多树木中的133Cs分布规律相比，转移到内心材的137Cs更少；但是，与133Cs的分布方式相比，还有一棵树木将137Cs过度转移到内部心材上。除了心材的高水分含量外，这种模式的产生还可能是由于事故后137Cs的大量叶吸收和根系吸收不良所致。137Cs / 133Cs浓度比的径向变化规律表明，与许多树木中的133Cs分布规律相比，转移到内心材的137Cs更少；但是，与133Cs的分布模式相比，还有一棵树将137Cs过度转移到内部心材上。除了心材的高水分含量外，这种模式的产生还可能是由于事故后137Cs的大量叶吸收和根系吸收不良所致。