The Doppler-shift attenuation method was used to obtain the following mean lifetimes (in psec) for the indicated nuclear levels: ${}_{}{}^{10}{}_{}{}^{}\mathrm{C}$(3.36), $\tau =0.155\mathrm{}\pm 0.025$; ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$(3.59), $\tau =0.150\mathrm{}\pm 0.015$; ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$(3.37), $\tau =0.189\mathrm{}\pm 0.020$; ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$(2.15), $\tau ={{2.7}_{-0.4\mathrm{}}}^{+0.5\mathrm{}}$. A limit of $\tau <30\mathrm{}$ fsec is obtained for ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$(1.74), which is a factor of 8 greater than, and therefore consistent with, the lifetime computed from the analog $\beta$ decay of ${}_{}{}^{10}{}_{}{}^{}\mathrm{C}$. Transition strengths obtained from the ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$(2.15) and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$(3.59) lifetimes are in good agreement with the effective-interaction calculations of Cohen and Kurath, as modified by Warburton et al. The ${}_{}{}^{10}{}_{}{}^{}\mathrm{C}$(3.36) and ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$(3.37) states decay by analog $E2\mathrm{}$ transitions: $2^{+}$, $T=1\mathrm{}\to 0^{+}$, $T=1\mathrm{}$, with $T_z=\pm 1$, whose strengths are well described by calculations of Kurath's for an effective charge ${\epsilon }_n={\epsilon }_p=0.5\mathrm{}$. An upper limit was obtained for the corresponding transition 5.17 → 1.74 in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(T_z=0)$ which is consistent (factor of 4 greater) with the analog strengths observed in the $T_z=\pm 1$ nuclei.

• Received 6 June 1968

DOI:https://doi.org/10.1103/PhysRev.176.1130