Search

ABSTRACTAnnually resolved radiocarbon (14C) measurements on tree rings led to the discovery of abrupt variations in 14C production attributed to large solar flares. We present new results of annual and subannual 14C fluctuations in tree rings from a middle-latitude sequoia (California) and a high-latitude pine (Finland), analyzed for the period 1030–1080 CE, to trace a possible impact of the Crab supernova explosion, occurring during the Oort minimum of solar activity. Our results indicate an increase of Δ14C around 1054/55 CE, which we estimate is higher in magnitude than the cyclic variability due to solar activity at a 2σ significance level. The net signal appears to be synchronized in the studied locations. Several sources of this event are possible including γ-rays from the Crab supernova, an unusually weak solar minimum or a solar energetic particle incident. More data are needed to provide more insight into the origin of this 14C event.

A systematic analysis of efficiency, reproducibility and accuracy of cryogenic purification of CO2 from air samples for isotopic analyses is presented. The technical characteristics of the cryogenic line are given in detail. To study the cryogenic process, three different operating parameters are considered: flow rate of the gas entering the line, pressure of the gas in the line, and CO2‐trap shape. Experimental results demonstrate that efficiency, reproducibility and accuracy strongly depend on the CO2trap shape. Moreover, a dependence of reproducibility and accuracy on the flow rate of the gas is found, but not on its pressure. High precision (≤0.02‰ for δ13C and ≤0.05‰ for δ18O) and good accuracy (<0.09‰ for δ13C and <0.14‰ for δ18O) is achieved after applying the N2O correction. Copyright © 2005 John Wiley & Sons, Ltd.