RESUMO
The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for 224Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of 224RaCl2 were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (Iγ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.
RESUMO
This paper describes the design of and first measurements with the new defined solid angle (DSA) alpha counter at the National Physical Laboratory, UK, with the aim of enabling high-precision radionuclide standardisations for alpha-emitting radionuclides and half-life measurements. The counter may be employed at three source-detector distances in order to monitor the measured activities with calculated geometrical efficiencies. Initial results are promising but further work is required to reduce the dominant uncertainty associated with the source activity distribution.
