High sensitivity detection of naturally occurring radiocarbon--I Chemistry of the counting sample

Details High sensitivity detection of naturally occurring radiocarbon--I Chemistry of the counting sample High sensitivity detection of naturally occurring radiocarbon--I Chemistry of the counting sample

Jul 1961

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1961gecoa..24..266t&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 24, Issue 3-4, pp.266-276

Mathematics

Logic

2

Scientific paper

The production of C 14 on the earth by cosmic rays has received wide attention as a means of determining the ages of archeological and geological samples. However, the low activities that must be measured necessitate devising special sensitive counting arrangements. This is particularly true if it is desired to extend the usefulness of the technique to materials several tens of thousands of years old or at the other end of the time scale, for samples only a few hundred years old. The most promising method of increasing the sensitivity of radiocarbon dating is the use of radiation detection techniques that are capable of counting large quantities of carbon. The liquid scintillation spectrometer is an instrument that has been applied in several cases to increase the efficiency of C 14 dating. This paper presents a means by which the entire counting solution (not including the small amounts of phosphors) can be synthesized from the sample to be dated. The solvent used is benzene, which is one of the most suitable materials for liquid scintillation counting since it contains 92 per cent carbon and shows no scintillation quenching properties. The chemistry involved in the complete synthesis of benzene is described in detail. The sample to be dated is burned and carbon dioxide collected in ammonium hydroxide solution. Strontium carbonate is precipitated upon the addition of strontium chloride. The dried carbonate is mixed with magnesium powder and strontium carbide is produced by ignition of the mixture in an evacuated stainless steel tube. Reaction of the carbide with water generates acetylene which is led into a circuit containing dry ice-cooled traps and a pyrolysis tube at 600°C. The acetylene polymerizes to benzene. This is collected in the cooled traps and then purified by distillation. The overall yield in the synthesis is 30 per cent. The chemical steps involve no special equipment or training. A 20-ml sample can be produced by two man-days of work and the entire procedure completed in less than a week.

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