Strength of theC10→B10(2155 keV)βBranch

A search for the $\beta$ decay of ${}_{}{}^{10}{}_{}{}^{}\mathrm{C}$ to the 2155-keV level in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ has been made in order to test the independent-particle-model predictions using mixed wave functions for the lowest two $J^{\pi }=1^{+}$ levels in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$. In contrast to a previously reported value of 6.4±2.0×${10}^{-5\mathrm{}}$ per ${}_{}{}^{10}{}_{}{}^{}\mathrm{C}$ decay for this branch, our results limit the strength to ≤8× ${10}^{-6\mathrm{}}$ with 90% confidence, and to ≤4× ${10}^{-6\mathrm{}}$ with 50% confidence. Comparison of this result with the strength of the $M1\mathrm{}$ transition between the 2155- and 1740-keV levels in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ shows that the ratio of orbital to spin contributions to the $M1\mathrm{}$ matrix element exceeds 3.5. When the Cohen-Kurath wave functions for the first two $J^{\pi }=1^{+}$ levels in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ are mixed in order to fit the strength of the 2155→ 1740-keV $M1\mathrm{}$ transition, the predicted $\beta$ branch to the 2155-keV level is at least 3 times as strong as the present experimental upper limit.