Nonobservation of12Ccluster decay of114Ba

By means of the on-line mass separator at Gesellschaft für Schwerionenforschung, Darmstadt, we produced ${}^{114}\mathrm{Ba}$ through the ${}^{51}{\mathrm{N}\mathrm{i}(}^{58}\mathrm{N}\mathrm{i},2n)$ reaction, separated it as a ${}^{114}{\mathrm{Ba}}^{19}{\mathrm{F}}^{+}$ beam, and implanted it into a stopper foil positioned in the center of an array of track detectors, which were used to search for ${}^{12}\mathrm{C}$ radioactivity of ${}^{114}\mathrm{Ba}$. A total number of $(5.4\mathrm{}\pm 1.7)\times {10}^4$ ${}^{114}\mathrm{Ba}$ atoms were implanted. No ${}^{12}\mathrm{C}$ event was found after a total exposure time of 116 h, corresponding to a ${}^{58}\mathrm{Ni}$ beam dose of $1.3\times {10}^{17}$. The resulting upper limit of $3.4\times {10}^{-5}$ (84% C.L.) for the branching ratio for ${}^{12}\mathrm{C}$ decay of ${}^{114}\mathrm{Ba}$ is considerably lower than the limits obtained in previous experiments, which represents an inconsistency at levels of more than 90%. A semiempirical estimate of 19.3 MeV for the upper limit of the $Q$ value for ${}^{12}\mathrm{C}$ decay of ${}^{114}\mathrm{Ba}$ is derived.