The electric quadrupole transition from the first $2^{+}$ state to the ground $0^{+}$ state in ${}^{16}\mathrm{C}$ is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive ${}^{16}\mathrm{C}$ nuclei. The measured mean lifetime is $77\pm 14(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 19(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\mathrm{p}\mathrm{s}$. The central value of mean lifetime corresponds to a $B(E2;2_1^{+}\to 0^{+})$ value of $0.63e^2{\mathrm{f}\mathrm{m}}^4$, or $0.26$ Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.

• Received 17 August 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.062501