Radon elimination during benzene preparation for radiocarbon dating by liquid scintillation spectrometry

Abstract

Radon gas is a serious contaminant in radiocarbon dating by radiometry. The low specific ionizations associated with the α-particle emitting radon and its β-particle emitting daughters overlap within the 14C counting window. Elimination of radon is therefore imperative for precise 14C age determinations. This paper deals with the sources and mechanism of incorporation of radon affecting 14C dating by liquid scintillation (LS) counting, and reviews conventional radon elimination practices in 14C laboratories. It demonstrates, based on rigorous multichannel and multiparameter α and β-particle spectral analyses of some 1000 benzene samples, that parent radium is not present and that its daughter radon is quantitatively eliminated during dynamic vacuum recovery of benzene at -78°C. However, the radon-free benzene can be recontaminated by exposure to air containing traces of radon, such as is common in concrete or low-lying laboratories. -from Authors