Evaluation of CO_2 fixation through dendrochronology for the wood grown in rain forest.

由于热带雨林中生长的树木由于缺乏明确的气候变化而不形成年轮，因此很难估计树木的年龄，因此很难知道该地区对二氧化碳的固定。为了进行树木年代学，我们测量了生长在热带雨林中的日本树种（Cryptomeria japonica）和印度尼西亚树种（Alstonia）木材的天然放射性，以及木材盘中元素分布和水分分布。在天然放射性测量中，我们建立了纯锗探测器的测量系统。^<210>的Pb放射性在年轮上由外向中依次降低。虽然放射性的衰减率与半衰期^<210>Pb的衰减率并不完全相等，但对于两种木材来说，Alstonia的年龄都是通过对日本柳杉的测量来估计的。在元素分析的情况下，进行了中子活化分析。对20多种元素进行了分析，发现Mg是估计树木年龄的一个有希望的元素，因为Mg浓度在木盘内呈线性变化。特别是对阿尔斯通树，中子射线照相不能显示其木龄。

Since the wood grown in a rain forest does not form annual rings because of lacking the definite change of the climate, it is difficult to estimate the age of the trees, therefore, the fixation of carbon dioxide at that area is difficult to know. To perform denderochronology, we measured the natural radioactivity of the wood as well as elemental distributions and water distribution in wood disks for both a Japanese tree (Cryptomeria japonica) and an Indonesian tree (Alstonia species) which was grown in a rain forest In the measurement of natural radioactivity, we set up the measuring system for a pure Ge detector. The ^<210>Pb radioactivity in a wood disk, across the annual rings, was reduces from outer to the center part. Though, the decreasing rate of the radioactivity was not exactly equal to that of the half-life of ^<210>Pb, for both wood species, the annual age of the Alstonia was estimated from the measurement of Cryptomeria japonica. In the case of elemental analysis, neutron activation analysis was performed. More than 20 elements were analyzed and was found that Mg was a promising element to estimate the age of the trees, for the Mg concentration was linearly changed within die wood disks. Especially for the Alstonia, the wood age was not shown from neutron Radiograph.