A search was made for an electron-positron pair transition from the 10.98-Mev $0^{-}$ state of ${\mathrm{O}}^{16}$ to the $0^{+}$ ground state using the ${\mathrm{F}}^{19}(p, \alpha ){\mathrm{O}}^{16*}$ reaction and an intermediate-image pair spectrometer. No 10.98-Mev pairs were observed with an intensity as great as 2×${10}^{-5\mathrm{}}$ that of the 3.86 Mev $M1\mathrm{}$ cascade gamma-ray from the 10.98-Mev to the 7.12-Mev $1^{-}$ state. This result suggests a lower limit of $\tau >2\mathrm{}\times {10}^{-8\mathrm{}}$ sec for the partial lifetime of a 10.98-Mev $0^{-}$→$0^{+}$ pair transition.

• Received 18 June 1958

DOI:https://doi.org/10.1103/PhysRev.112.488