LSC STANDARDIZATION OF CA-45 BY THE CIEMAT/NIST EFFICIENCY TRACING METHOD

A commercial solution of (CaCl2)-Ca-45 and two organic compounds, Ca-45-2-ethylhexadecanoate and Ca-45-HDEHP complex, synthesized in the laboratory, have been used to produce appropriate sources for LSC measurements. A toluene-based scintillator and three commercial cocktails (Hisafe II, Ultima Gold and Instagel) were used for measuring the samples. Their concentration quenching, time stability, and spectral behaviour were studied over a 30-day period. The stable samples were used to standardize the radioactive solutions by the CIEMAT/NIST efficiency tracing method. Experimental quench curves for H-3 were measured with each scintillator to cover the range of figure of merit between 1 and 4, corresponding to H-3 equivalent efficiency between 52 and 12%. Experimental and computed efficiencies were in good agreement, with individual discrepancies lower than 0.6% in all cases; high efficiency values, better than 95%, were obtained with unquenched samples. A combined uncertainty of 0.4% was obtained for the activity concentration estimation of each radioactive solution.