Intensities and Spectrum of Cosmic Rays in the past of 25000 years

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We have measured the ^<14>C concentrations in single-year tree rings of old wood, using a multicathode by accelerated mass spectrometry (AMS). The ^<14>C concentrations of ten single-year tree rings were measured at intervals of 10, in 100 tree rings. For each single-year tree ring sample, typically 80 measurements of the ^<14>C concentrations were carried out using multicathodes. The sample standard deviations indicated that there are other fluctuations of typically 1.5% in addition to the fluctuation of the Poisson counting statistics that is typically 3% for each measurement. The average radiocarbon date of the tree rings was 22,130±306 BP for all 624 data measured by the multicathodes for the single-year tree ring samples. From the calibration data of Lake Suigetsu, the calendar dates of these one hundred tree rings were located between cal 25,400 yr BP and cal 26,150 yr BP. The radiocarbon dates changes between 21,979 Bp and 22,272 BP with error of approximately 50 BP, corresponding to the precision of approximately 0.5%. There was a step with a change of approximately 144 BP for each ten years in the time profile.