Abstract
The half-life of radium-223 has been determined simultaneously by microcalorimetry and proportional alpha counting, with 5 mc of radium-223 separated from actinium-227 and thorium-227 by cation exchange. A 4-mc fraction of the purified radium-223 was transferred to a tantalum capsule, dried, ignited at red heat, and hermetically sealed. The remainder was distributed among ten stainless steel disks in fractions ranging from 0·15 to 0·001 mc. The heat output of the tantalum capsule was measured in an isothermal resistance bridge microcalorimeter for 35 days, and in an isothermal thermoelectric microcalorimeter for 96 days. The stainless steel disks were alpha-counted in a windowless gas-flow proportional counter for 172 days. The half life of radium-223 was found to be 11·4347 ± 0·0011 days by microcalorimetry and 11·4267 ± 0·0062 days by proportional counting. The weighted average was 11·4346 ± 0·0011 days.
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