Isotope Effect in the Benzene Synthesis for Radiocarbon Dating

Abstract

As an alternative to the common gas sample methods for radiocarbon dating, liquid scintillation counting has been used and is being improved on. Relatively recently, a practically complete synthesis of benzene, one of the most efficient liquid scintillation materials, has been developed in Texas^1,2 and, independently, in the U.S.S.R.³. The liquid, containing 92 per cent carbon, all of which comes from the sample being dated, can be produced in approximately 50 per cent yields in 8 h or less. The liquid scintillation counter, now in widespread use in biological and chemical tracer work, is well known for its exceptional reliability. Improvements in the photomultipliers and the introduction of fast electronics, which have substantially reduced the resolving time of the coincidence unit, have increased the counting efficiency for radiocarbon to 75 per cent or more. This is comparable to the gas sample counters. The stability of the liquid scintillation counter seems to be as good as that of the best gas counters.