Abstract
A study has been continued of 14C-dating method by liquid scintillation counting. In this technique, sample of either large or small volume can be accomodated, and when using large amount of sample, statistical errors in counting can be made smaller than in the case of gas counting. The authors have been using methanol or methyl-borate containing sample carbon as a solvent of scintillation solution because of ease of synthesis and effectiveness in counting.
Firstly, old organic samples were converted, successively, into charcoal, *CO2, (NH4) 2 *CO3, and finally, into Ca*CO3. Perchloric acid was poured into the Ca*CO3 and *CO2 was again evolved. The *CO2 was blown into diethyl-carbitol solution of LiAlH4 and to produce LiAl (CH3O) 4 and then the LiAl (CH3O) 4 was decomposed by adding butyl carbitol to obtain methanol.
The CH3OH was carefully purified and the purity was verified both by elementary analysis and by gas chromatography. The yield was about 70% of Ca*CO3. The scintillator containing the methanol and toluene in the ratio of 1: 1 showed counting efficiency of 26%. Methyl-borate was also prepared from methanol and B2O3. Counting efficiency of the scintillator containing 60% methyl-borate and 40% toluene was 52%.
