A study of the solar activity variability in the past millennium by precise radiocarbon measurement

该项目的目的是利用加速器质谱仪，利用太阳活动极小期树轮中的放射性碳，研究近千年来太阳活动的变化和行星际磁场的结构。为此，我们制作了样品，并非常小心地测量了高精度的放射性碳含量，并试图在斯波勒和蒙德米尼玛找到放射性碳含量的微小变化。使用名古屋大学的加速器质谱仪(AMS)，在样品制备和运行过程中如何实现高精度的测量是我们关注的问题。利用该系统可以制备出高质量、均匀的样品，通过对标准样品的评价，可以达到0.2%的高精度。在实际测量中，总体误差取决于AMS的测量时间和稳定性，由统计误差决定。虽然机器维护使长时间测量和大目标电流的高精度测量变得困难，但对同一树轮样品重复测量可以实现高精度，我们从蒙德极小值和斯波勒极小值两个角度高精度地测量了树轮样品中的放射性碳含量。对时间序列数据的分析提供了关于太阳活动极小期宇宙线流量变化的知识。结果表明，太阳活动的11年变化即使在大极小期也存在，但11年的变化在深极小期可能较弱，周期长度通常为11年，在极小期可能更长，并出现太阳磁场反转的迹象。我们还测量了公元1000年左右的放射性碳含量。我们发现了一种可能源于11年太阳活动变化的周期结构，并讨论了公元1006年超新星爆发效应的可能性。

This project aimed to investigate variability of solar activity and structure of interplanetary magnetic field in the last millennium by radiocarbon in tree rings during grand minima of solar activity with accelerator mass spectrometry. For this purpose we prepared samples and measured radiocarbon content with great care on high precision and tried to find small change of radiocarbon content in the Spoerer and Maunder Minima. An accelerator mass spectrometer(AMS) of Nagoya University was used.We took care how high precision measurement could be achieved in preparation of samples and also in operation of AMS. We could prepare samples with high quality and uniformity by using the system constructed in this project and showed that high precision of 0.2% is achievable by evaluation of standard samples. In actual measurement overall error is determined by statistical error depending on measurement time and stability of AMS. Although the machine maintenance made it difficult to try long measurements and large target current for high precision, repeat of measurement for the same tree ring samples could realize the high precision.We measured radiocarbon content in tree ring samples from the Maunder Minimum and the Spoerer Minimum with high precision. Analysis of time sequential data gives knowledge on variation of cosmic ray flux during the solar activity minima. It was revealed that the 11-year variation of solar activity exists even in the grand minima, however, the 11-year variation could be weak in deep minima, the cycle length, which is normally 11 years, might be possibly longer in minima, and signs of reversal of solar magnetic field are seen. We also measure radiocarbon contentin the period of around AD1000. We found a periodic structure probably due to 11-year solar activity change and discussed a possibility of the effect of supernova explosion in AD1006.