Study of the performance of efficiency tracing technique on a TRICARB 2100TR liquid scintillation analyzer

The liquid scintillation Efficiency Tracing (ET) technique is a practical method of quantify radionuclides being analyzed in a liquid scintillation analyzer. This technique has several advantages over conventional liquid scintillation methods: i) no quench curve (quenched standard set) is required for each nuclide being analyzed; ii) the technique can be used effectively for almost all pure beta and beta-gamma emitters (minimum energy = 70 keV); iii) only a single unquenched 14C sample (same as that used to normalize the liquid scintillation analyzer) is required to calculate radionuclide activity (DPM) or concentration; iv) the efficiency tracing techniques provides a simple method for quantify of DPM in the sample; v) relatively small errors (1-5%) in the calculation of DPM are reported in literature; vi) different radionuclides can be intermixed in the sample batch. The most important disadvantages are: i) is not applicable to tritium and to radionuclides which decay by isomeric transitions and electron capture; ii) for samples of low count rates (<1500 cpm), it is recommended that one use a conventional method, which utilizes quench correction curves. Radiation Protection and Environmental Protection Laboratory from the Institute for Nuclear Research - Pitesti is endowed with a Tri-Carb Liquid Scintillation Analyzer, model 2100TR. A series of experimental works were performed to assess performances of Efficiency Tracing method. In order to verify the usefulness of the technique, prepared samples containing known amounts of 14C activities were tested. The experimental tests were made using both the ET method implemented on the analyzer by the producer and our ET method, using the reference spectrum of the unquenched 14C standard, used to normalize the liquid scintillation analyzer. The results indicate that the measured values using implicit ET method are in good agreement (uncertainty ≤ 3%) with the reference values only for samples with a quenching level not very high (quenching indicating parameter tSIE > 200 - 300). Otherwise, using our ET method, good results (percent recovery more than 95%) were obtained for any quenching level (tSIE > 100) even at a count rate level lower one magnitude order than that is recommended for this method. (authors)