title: Measurement of the 225Ac half-life.
abstract: The (225)Ac half-life was determined by measuring the activity of (225)Ac sources as a function of time, using various detection techniques: α-particle counting with a planar silicon detector at a defined small solid angle and in a nearly-2π geometry, 4πα+β counting with a windowless CsI sandwich spectrometer and with a pressurised proportional counter, gamma-ray spectrometry with a HPGe detector and with a NaI(Tl) well detector. Depending on the technique, the decay was followed for 59-141 d, which is about 6-14 times the (225)Ac half-life. The six measurement results were in good mutual agreement and their mean value is T(1/2)((225)Ac)=9.920 (3)d. This half-life value is more precise and better documented than the currently recommended value of 10.0 d, based on two old measurements lacking uncertainty evaluations.
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium. stefaan.pomme@ec.europa.eu
authors.forename: S
authors.initials: S
authors.lastname: Pommé
authors.forename: M
authors.initials: M
authors.lastname: Marouli
authors.forename: G
authors.initials: G
authors.lastname: Suliman
authors.forename: H
authors.initials: H
authors.lastname: Dikmen
authors.forename: R
authors.initials: R
authors.lastname: Van Ammel
authors.forename: V
authors.initials: V
authors.lastname: Jobbágy
authors.forename: A
authors.initials: A
authors.lastname: Dirican
authors.forename: H
authors.initials: H
authors.lastname: Stroh
authors.forename: J
authors.initials: J
authors.lastname: Paepen
authors.forename: F
authors.initials: F
authors.lastname: Bruchertseifer
authors.forename: C
authors.initials: C
authors.lastname: Apostolidis
authors.forename: A
authors.initials: A
authors.lastname: Morgenstern
mesh_terms: D000186:Actinium / Q000737:chemistry*; D000512:Alpha Particles; D006207:Half-Life; D011829:Radiation Dosage; D011851:Radioactivity
chemical_list: D000186:Actinium