Standardization of electron-capture radionuclides by liquid scintillation counting

Liquid scintillation counting has proven to be an excellent technique to standardize beta-ray emitters with good accuracy. However, the success achieved in beta-ray nuclide standardization is not extensible for radionuclides decaying by electron-capture. Last comparison of 55Fe revealed discrepancies of 5% among laboratories. This paper presents two new versions of the computer program EMI. First we consider a better simulation of the photoelectric interaction of X-rays with the scintillator cocktail (EMI 1.2); and second, a more sophisticated KL1L2L3M atomic rearrangement model (EMI 2.0). We emphasize the importance of improving the simulation of the electron capture process to achieve better standardization of electron-capture nuclides by the CIEMAT/NIST method.