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A study of cosmic ray spectrum in ancient time with the measurement of the time variations of cosmic rays 15000 years past

通过测量15000年前宇宙线的时间变化来研究远古宇宙线光谱

基本信息

批准号：
12640251
负责人：
SAKURAI Hirohisa
金额：
$ 2.3万
依托单位：
YAMAGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12640251/
关键词：
Cosmic rays Radiocarbon Carbon Cycle 15000 years past Ultra low-level liquid scintillation counting system AMS measurement 宇宙線 AMS

项目摘要

Study of secular variations of cosmic rays provides us one of the clues to investigate origin, propagation, and acceleration of cosmic rays. Also, solar activities and geomagnetic variation affect the intensity of cosmic rays incoming to the earth and hence the measurement of the time variations of cosmic rays in the past time allows to know past solar activity and past environment of the earth. Here, we measured the cosmogenic radioisotope C-14 in a piece of wood buried in a stratum at Yamagata prefecture. The stratum was layered in about 250 years for 2000 years from 13000 years past. The extraction rates of the wood samples were 25 % and 5 % for the conditions of the wood and sub-charcoal, respectively. The radiocarbon age of the sample was 13756±51 year BP with ultra-low level liquid scintillation counting system of the accuracy of 0.2 %. The radiocarbon ages for the samples of five layers with AMS were like in line as a function of the depth except a sample. The difference of the ages was approximately 1500 years for the 3 m deep. However, the age of one sample was about 1000 years younger than the estimated age from each sample of the layers of the stratum. It implies that the concentration of C-14 around 13500 year BP past changed with the time scale of 300 years. This study indicates that the measurements of radiocarbon ages are effective for the investigation of C-14 variations and hence of time variation of cosmic rays employing the accumulated layer of the stratum.

宇宙线长期变化的研究为我们研究宇宙线的起源、传播和加速提供了线索之一。此外，太阳活动和地磁变化会影响进入地球的宇宙射线的强度，因此测量过去宇宙射线的时间变化可以了解过去的太阳活动和过去的地球环境。在这里，我们测量了宇宙成因的放射性同位素C-14在一块木头埋在一个地层在山形县。从13000年前的2000年到250年左右，地层分层。木材样品的提取率分别为25%和5%的木材和木炭的条件下，分别。用准确度为0.2%的超低水平液闪计数系统测得样品的放射性碳年龄为13756±51年。除一个样品外，其余5个样品的AMS测年结果与深度呈线性关系。3 m深处的年龄差异约为1500年。然而，一个样本的年龄比地层各层样本的估计年龄小约1000年。这意味着13500年BP前后的C-14浓度在300年的时间尺度上发生了变化。本研究表明，放射性碳年龄的测量对于利用该地层的累积层研究C-14的变化，从而研究宇宙线的时间变化是有效的。