Liquid Scintillation Techniques for Radiocarbon Dating

A study has been made of the merits of liquid scintillation methods for radiocarbon dating. The synthesis of toluene from sample carbon, and the use of this liquid in a 20 cc cell, in combination with the best available photomultiplier tube, gave results which indicate that this method can be of significance for samples of age 45 000 years, for a 48 hour counting period. A background counting rate of 3.34 cpm was obtained with ``old'' toluene and adequate shielding and pulse height discrimination, but without photomultiplier cooling or the use of coincidence-anticoincidence arrangements. This method suffers, however, from a rather elaborate chemical synthesis, so that a simpler diluent technique was studied, involving the synthesis of methanol from sample carbon. This method is suitable for routine analysis, and gave results indicating a significance to 37 000 years, the decreased accuracy of the method being the result of the somewhat lower fluorescence efficiency of the scintillating mixture. There is evidence that a routine methyl borate diluent method will give an accuracy comparable to that of the toluene method.