Utilising a chemically purified solution the radioactive half-life of 227Th has been determined indirectly by observation of the ingrowth of 223Ra using an ionisation chamber (IC) and for the first time by direct observation of the change in activity with time using a high-purity germanium (HPGe) gamma-ray spectrometer. The radioactive decay was observed for ~ 104 days (~ 5.6 half-lives) by gamma-ray spectrometry and approximately 63 days and 72 days (~ 3.4 and ~ 3.9 half-lives) using an ionisation chamber (IC). The resulting half-life values – 18.695 (4) days (IC) and 18.683 (20) days (HPGe) – are consistent and detailed uncertainty budgets are presented for the two measurement techniques. The weighted mean of both results, 18.695 (4) days, is inconsistent with the most precise published half-life value of 18.7176 (52) days (Jordan and Blanke, 1967). A critical evaluation of literature data has been performed, indicating a paucity of reliable and independent measurements. The power-moderated weighted mean of selected independent published values is T1/2(227Th) = 18.697 (7) days. A method has been provided for modification of the estimated half-life of 227Th, determined by the ingrowth technique, in this work if a different evaluated 223Ra half-life would be used.

COLLINS S.;  POMME Stefaan;  JEROME S. M.;  FERREIRA K. M.;  REGAN P. H;  PEARCE A.; 

2015-08-28

PERGAMON-ELSEVIER SCIENCE LTD

JRC95245

0969-8043,   

http://www.sciencedirect.com/science/article/pii/S0969804315300828,    https://publications.jrc.ec.europa.eu/repository/handle/JRC95245,   

10.1016/j.apradiso.2015.07.001,