NEWLY DESIGNED 0.8-ML TEFLON(R) VIAL FOR MICROVOLUME RADIOCARBON DATING

We have tested two versions of an 0.8-ml volume Teflon(R) vial, design ed specifically for radiocarbon dating in the microvolume range, using a modern Quantulus 1220(TM) liquid scintillation (LS) spectrometer. W e determined the counting performance of each vial type in conjunction with different designs of copper holder, viz., with and without the i ncorporation of a ''Teflon(R) light coupler''. We also compared the lo sses of sample benzene during a typical 28-day counting period. Result s show that neither vial design nor the type of vial holder used in th e intercomparison had a significant influence on counting performance. We recorded an absolute C-14 detection efficiency of 82% against a ba ckground count rate of 0.1 cpm, ie., a ''figure of merit (FM) value'' = 67,240. This compares favorably with the operational parameters anti cipated for microvolume C-14 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.