A Study of Cosmic Ray Spectrum due to Measurements of yearly time variations for Cosmic Ray Intensity in the Past 2500 year

点击翻译按钮获取中文摘要

There are no data related to the 11-year cycle for more distant times (I.e. > 1000 years ago). To address this, we have started to measure, at single year intervals, the concentrations of 14C in old tree rings of wood buried ca. 2500 years ago by a volcanic eruption. (1) Constructed highly accurate 14C measuring system is composed of a benzene synthesizer capable of producing a large quantity (10 g) of benzene and a Quantulus 1220TM liquid scintillation counting system. (2) The accuracy is < 0.2% for measurements of the 14C concentration for single-year tree rings. (3) To estimate the calendar age of the wood, we carried out 14C dating for three tree rings form the wood, sequentially separated by 100 years and 130 years. The results were 2475 B.P., 2503 B.P., and 2410 B.P. for the rings, respectively. From these results, the wood most probably dates from 485 B.C., using Stuiver's calibration data. (4) We have sequentially measured the concentrations of the 8 single year tree rings. The standard deviation was 0.3% for the average and the maximum variation was 0.5%. Using our 14C measuring system for the single year tree rings, we can investigate the cosmic ray spectrum in the ancient time for variations of 0.3% 14C concentrations corresponding to 30% variations of cosmic ray intensities.