Study of the solar activity in the past by measurement of radiocarbon in tree rings

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In order to investigate the variability of solar activity in the last millenium, the concentrations of radiocarbon in Yaku ceder tree rings have been measured. Until now, we have produced samples and measured the concentration of radiocarbon for the Spoerer minimum when the solar activity was lowered. The cellulose samples of AD1410 to 1480 were converted to benzene and radiocarbon activity was measured by the liquid scintillation (LSC) method. For the samples of AD1480 to 1530, radiocrbon activity was measured by the accelerator mass spectometry (AMS) because enough amount of benzene with high purity was not obtained. While a hundred gram of wood samples are necessary for good statistical accuracy for LSC method, only 10 mg is sufficient for AMS method. At present, obtainable accuracy is 0.3 to 0.4 % for LSC method and 0.4 to 0.5 % for AMS method. Although our final goal is the accuracy of 0.2 to 0.3 %, we have measured in rather worse accuracy as a first step.Until now, radiocarbon contents have been measured for almost all yearly samples of AD1410 to 1480 and for every wo year samples of AD1480 to 1530. Some samples were measured by the both method and the same activity was obtained within the error. Our results agrees well with the decadal radiocarbon contents in tree rings of North America by Stuiver.The variation of our radiocarbon contents is within ±0.5 % after removing the long term trend. This differ from the result for the tree rings of the Maunder minimum by Kocharov. Our periodicity analysis by MEM method shows a dominat peak of spectral density at 21 year. This is the same trend as that obtained for the Maunder minimum. The sun and interplanetary space might have different mechanism and structure of magnetism in the grand minima.