41Ca standardization by the CIEMAT/NIST LSC method

A procedure for the liquid scintillation counting standardization of the electron-capture nuclide 41Ca has been successfully developed and applied with 41CaCl2 and 41Ca-(HDEHP)n samples synthesized in the laboratory from 41CaCO3 supplied by Oak Ridge National Laboratory. Six scintillators were tested: the organic samples were stable in toluene—alcohol, Ultima-Gold™ and HiSafe III™ for 30 d, whereas the inorganic samples were only stable in toluene—alcohol and HiSafe III™ for the same period of time. Despite of the low counting efficiencies (1%–13%) due to the very low-energy of less than 3.6 keV of the X-rays and Auger electrons of 41Ca, the stable samples were standardized by the CIEMAT/NIST method to a combined uncertainty of 2.4% over a range of figures of merit of 1.75 to 7.25 (3H equivalent efficiency of 40% to 7%).