Newly Designed 0.8-ML Teflon(R) Vial for Microvolume Radiocarbon Dating

Abstract

We have tested two versions of an 0.8-m1 volume Teflon(R) vial, designed specifically for radiocarbon the microvolume range, using a modern Quantulus 1220(TM) liquid scintillation (LS) spectrometer. We determined the counting performance of each vial type in conjunction with different designs of copper holder, viz., with and without the incorporation of a "Teflon(R) light coupler". We also compared the losses of sample benzene during a typical 28-day counting period. Results show that neither vial design nor the type of vial holder used in the intercomparison had a significant influence on counting performance. We recorded an absolute 14C detection efficiency of 82% against a background count rate of 0.1 cpm, i.e., a "figure of merit (FM) value" = 67,240. This compares favorably with the operational parameters anticipated for microvolume 14C dating by modern LS spectrometry. However, variations in the design of the sealing method used between the vial types was reflected in an apparent approximate tenfold difference in the amount of benzene lost during routine counting. In the better case, the evaporation loss was equivalent to 0.032 mg of benzene per day.