RESUMEN
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.
RESUMEN
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 4πß(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 T1/2 = 6.6489(52) d.