By means of a coincidence method it is shown that the $\frac{5}{2}+$ state of ${\mathrm{C}}^{13}$ at 3.86 Mev has an $E2\mathrm{}$ branch of relative strength (9.3±2.0)×${10}^{-3\mathrm{}}$ to the ½+ state at 3.09 Mev. From consideration of the likely strengths of the competing $E1\mathrm{}$ transition to the $\frac{3}{2}-$ state at 3.68 Mev and the $M2\mathrm{}$ transition to the ground state it is deduced that this branching ratio implies an $E2\mathrm{}$ transition speed of the order of a single-particle (proton) unit. This in turn demands the substantial participation of at least one excited state of ${\mathrm{C}}^{12}$ in the parentage of at least one of the ${\mathrm{C}}^{13}$ states with respect to the $1d$ or $2s$ neutron. This eliminates in particular a $\mathrm{jj}$-coupling description of ${\mathrm{C}}^{13}$ in which the two states in question are $1d_{\frac{5}{2}}$ and $2s_{\frac{1}{2}}$ neutron states and more generally a weak-coupling model in which the ground state of ${\mathrm{C}}^{12}$ is the unique parent for the ${\mathrm{C}}^{13}$ states (with respect to $1d$ and $2s$ neutrons).

• Received 22 June 1960

DOI:https://doi.org/10.1103/PhysRev.120.943