The standardization of 177Lu by 4πβ liquid scintillation spectrometry with 3H-standard efficiency tracing

Solutions containing the potential radiotherapy radionuclide 177Lu have been standardized at the National Institute of Standards and Technology (NIST) by 4πβ liquid scintillation (LS) counting with 3H-standard efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were made with 4π NaI(Tl) γ-ray spectrometry. Activity determinations were made on 4 solutions over the course of 10 months with an expanded (k=2) uncertainty on the activity of 0.8%. Half-life measurements were carried out using the NIST “4π” γ ionization chamber (IC) and LS counting and gave a new value of 6.65±0.01 d, which is shorter than the current ENSDF-recommended value by 1.3%. Impurity analyses were performed by high-purity germanium (HPGe) γ-ray spectrometry and indicated only the presence of 177mLu at a level of 0.02% that of the 177Lu as of the respective reference times for the four solutions. Calibration factors for the NIST IC and Vinten 671 ionization chambers were developed, as were dial settings for the NIST-maintained Capintec CRC-12.