Measurement of the activity and determination of the half-life of 225Ac at POLATOM

A method for absolute measurements of the 225Ac activity in equilibrium with its progeny was developed. Measurements were performed using the triple-to-double coincidence ratio (TDCR) method in two different TDCR counters. The activity concentration of an 225Ac solution was determined and the solution was sent to the SIR system for a comparison. The half-life of 225Ac was determined by one of the TDCR counters and found to be 9.9150(63) days.

The international reference system for beta-particle emitting radionuclides: Validation through the pilot study CCRI(II)-P1.Co-60

The Bureau International des Poids et Mesures (BIPM) is developing a new transfer instrument to extend its centralized services for assessing the international equivalence of radioactive standards to new radionuclides. A liquid scintillation counter using the triple/double coincidence ratio method is being studied and tested in the CCRI(II)-P1.Co-60 pilot study. The pilot study, involving 13 participating laboratories with primary calibration capabilities, validated the approach against the original international reference system based on ionization chambers, which has been in operation since 1976. The results are in agreement and an accuracy suitable for purpose, below 5×10-4, is achieved. The pilot study also reveals an issue when impurities emitting low-energy electrons are present in the standard solution, which have a different impact on liquid scintillation counting compared to other primary measurement methods.

Activity standardization and half-life measurement of 177Lu

The activity of the ¹⁷⁷Lu solution has been measured by means of the CIEMAT/NIST efficiency tracing method. This result has been compared to the previous obtained results received from 4πβ(LS)-γ coincidence and anticoincidence counting. The activities determined with various methods have been found to be consistent. The decay curve of the ¹⁷⁷Lu solution has been followed in the TDCR counter to determine the half-life of this isotope. The half-life has been separately determined for double and triple coincidence events. The arithmetic mean value of these two results has been found to be T_1/2 = 6.6489(52) d.