PNNL

Abstract

There is significant interest in the use of terbium radioisotopes for applications in cancer therapy and diagnosis. Of these, 161Tb, a medium energy beta- and prolific auger emitter, is being investigated as a potential alternative to 177Lu. The higher proportion of conversion electron and Auger electron emissions, and variety of low-energy gammas make 161Tb an attractive targeted theranostic. As a product of nuclear fission, 161Tb is also of importance to nuclear forensics. The current evaluated half-life of 6.89(2) d has a standard uncertainty that contributes significantly to the standard uncertainty of decay calculated activity determination. Furthermore, the accuracy of this evaluated half-life has been called into question by measurements reported recently at the Institute of Radiation Physics (IRP), Switzerland. In this work, the half-life of 161Tb was measured at three independent laboratories located in the United Kingdom and United States of America for a total of five determinations using three independent measurement techniques. The half-life determined for 161Tb of 6.9637(29) d confirms the observed 1 % relative increase observed by IRP, though the reported half-lives in this work and at IRP are significantly different (z-score = 3.1).