title: Activity determination of227Ac and223Ra by means of liquid scintillation counting and determination of nuclear decay data.
abstract: The activity concentrations of solutions containing227Ac and223Ra in equilibrium with their progenies, respectively, were measured by means of liquid scintillation counting. The counting efficiencies were determined with the aid of a free parameter model. The corresponding calculations comprise the computation of several alpha, beta and beta/gamma branches. For short-lived progenies like215Po the counting efficiency depends on the counter dead time. Measurements were made in custom-built triple-to-double coincidence ratio (TDCR) systems and various dead-time adjustments were used. In addition, two commercial counters were used to apply the CIEMAT/NIST efficiency tracing technique using3H as a tracer. For the227Ac solution, the overall relative standard uncertainty of the activity concentration was found to be 0.93%. The dominant uncertainty components are assigned to the efficiency computation of the low-energy beta transitions of227Ac. We have identified a need for improved227Ac decay data to achieve a significant reduction in the overall uncertainty. In the case of223Ra, the activity concentrations were determined with relative standard uncertainties below 0.3%. Hence, PTB is prepared to provide calibration services for223Ra, which is an isotope of increasing interest in nuclear medicine. The TDCR measurements were also used to determine the half-life of223Ra. The decay was followed for about 58 days and a half-life T1/2=11.4362(50)d was obtained.
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany. Electronic address: Karsten.Kossert@ptb.de.
authors.forename: Karsten
authors.initials: K
authors.lastname: Kossert
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany.
authors.forename: Karen
authors.initials: K
authors.lastname: Bokeloh
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Dersch
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany.
authors.forename: Ole
authors.initials: O
authors.lastname: Nähle
keywords: (223)Ra; (223)Ra half-life; (227)Ac; Liquid scintillation counting; Photon emission probabilities; TDCR