Discovery of Radioactive Decay ofRa222andRa224byC14Emission

Abstract

Using the ISOLDE on-line isotope separator at CERN to produce sources of ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$, ${}_{}{}^{221}{}_{}{}^{}\mathrm{Ra}$, ${}_{}{}^{222}{}_{}{}^{}\mathrm{Ra}$, ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$, and ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$, and using polycarbonate track-recording films sensitive to energetic carbon nuclei but not to alpha particles, we have discovered two new cases of the rare ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ decay mode—in ${}_{}{}^{222}{}_{}{}^{}\mathrm{Ra}$ and ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$. Our results for branching ratios, $B$, relative to alpha decay are for ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$ and ${}_{}{}^{221}{}_{}{}^{}\mathrm{Ra}$, $B<\mathrm{}4.4\mathrm{}\times {10}^{-12\mathrm{}}$; for ${}_{}{}^{222}{}_{}{}^{}\mathrm{Ra}$, $B=(3.7\mathrm{}\pm 0.6)\times {10}^{-10\mathrm{}}$; for ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$, $B=(6.1\mathrm{}\pm 1.0)\times {10}^{-10\mathrm{}}$; for ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$, $B=(4.3\mathrm{}\pm 1.2)\times {10}^{-11\mathrm{}}$.