PERFORMANCE OF THE PACKARD TRI-CARB(R) 2770TR SL LIQUID SCINTILLATIONANALYZER FOR C-14 DATING/

We present results that demonstrate the potential of the Packard Tri-C arb(R) Model 2770TR/SL for radiocarbon dating. For 2 g of sample benze ne, a stable background count rate of 0.307 cpm and a stable counting efficiency of 64.78% were determined using a 13-75 keV counting window . Changes to the mathematical routines for t-SIE (quench indicating pa rameter) calculation and a reduction in the activity of the external s tandard have enabled stability of the t-SIE to be achieved, and combin ed with the use of a suitable balance point counting window; all of th ese factors give the stability of performance required for C-14 dating . Calculations based on the above parameters indicate that the limit o f detection for 2 g samples, counted for 5000 min, is >48,900 yr sp. T he great advantage of this system is that these data were acquired usi ng inexpensive standard 7-mL low potassium borosilicate glass vials. V ial holders manufactured from BGO reduced the background to 0.15 cpm w ith a minimum effect on efficiency (64.46% for 13-75 keV). A similar c alculation of the limit of detection gave >51,700 sp. The use of the B GO vial holders in other instruments employing time-resolved liquid sc intillation counting (TR-LSC) (Models 2250CA and 2260XL) also brought about significant improvements in detection limits.