Lifetime of the isomeric 02+ state in 12Be

Mean lifetime τ of the isomeric 02+ state in 12Be has been determined by measuring decay spectra of delayed γ-rays from stopped 12Be nuclei produced by the projectile fragmentation of 18O at 100 A MeV. A consistent value of τ=331±12ns was obtained from the time spectra of the E2 γ decay to the 21+ state and the positron annihilation following the E0 decay to the ground state. Based on the observed branching ratio between the E2 and E0 decays, transition strengths of the two decay modes were deduced to be B(E2;02+→21+)=7.0±0.6e2fm4 and |〈02+|∑ieiri2|01+〉|=0.87±0.03efm2, respectively.