Standardization of 237Np

The standardization of 237Np was investigated. The certified massic activity for 237Np was obtained by 4παβ liquid scintillation (LS) counting with correction for the 233Pa daughter using the CIEMAT/NIST efficiency tracing method using a 3H standard. Confirmatory measurements were also performed by high-resolution HPGe gamma-ray spectrometry, and by 4παβ(LS)-γ(NaI) anticoincidence counting. All results agree within the respective method's uncertainties. It was confirmed that the 237Np/233Pa radioactive equilibrium is disturbed when making dilutions and/or removing aliquots.