The possible $0^{-}$ →$0^{+}$ ground-state pair decay of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ 10.95- MeV $0^{-}$ state was reinvestigated using the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(p, \alpha ){}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ reaction at $E_p=5.4-5.7\mathrm{}$ MeV and a magnetic pair spectrometer. A previously reported pair peak of 3.84 MeV due to the 10.952→7.117-MeV transition was not observed. The data indicate a much smaller relative population of the 10.95-MeV state in this reaction than reported previously and this places doubt on the upper limit derived earlier for the $0^{-}$ →$0^{+}$ ground-state pair decay. In a test of the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^3{}_{}{}^{}\mathrm{He}, p){}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ reaction at $E_{{}_{}{}^3{}_{}{}^{}\mathrm{He}}=4\mathrm{}$ MeV the yield was too low to study the 10.95-MeV state. Using the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}(d, p){}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ reaction at $E_d=4.5\mathrm{}$ MeV the $0^{-}$ →$0^{+}$ ground-state branch from the 6.90-MeV $0^{-}$ state of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ was found to be<1.1 × ${10}^{-4\mathrm{}}$ via pair decay. The corresponding lifetime limit, $\tau {(0^{-}\to 0^{+})}_{e^{+}{e}^{-}}>3\mathrm{}\times {10}^{-10\mathrm{}}$ sec, is not considered significant. It is concluded that a sensitive search for M0 pair transitions remains to be made.

NUCLEAR STRUCTURE ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$: measured ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(p, \alpha )$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}(d, p)$ pair spectra; previous results on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ 10.95-MeV $\tau {\mathrm{}\left(M0\mathrm{}\right)\mathrm{}}_{e^{+}{e}^{-}}$ not confirmed; deduced lower limit on ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ 6.90-MeV $\tau {\mathrm{}\left(M0\mathrm{}\right)\mathrm{}}_{e^{+}{e}^{-}}$.

• Received 9 February 1978

DOI:https://doi.org/10.1103/PhysRevC.18.576