The Doppler shift attenuation method has been used to make two measurements of the mean life of the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ 320-keV level. The results are 150±30 fs from the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(t, \mathrm{p}\gamma ){}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ reaction and 168±17 fs from the ${}_{}{}^3{}_{}{}^{}\mathrm{H}({}_{}{}^9{}_{}{}^{}\mathrm{Be}, \mathrm{p}\gamma ){}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ reaction. The adopted value of 166±15 fs, from the present and previous measurements, corresponds to an extremely strong $E1\mathrm{}$ transition of 0.36±0.03 W.u. The adopted energy of the ground state transition from this and previous measurements is 320.04±0.10 keV. It is shown that the magnitude of this $E1\mathrm{}$ transition can be understood on the basis of shell-model calculations only if realistic single-particle wave functions are used. A similar theoretical treatment is given for strong $E1\mathrm{}$ transitions in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$.

NUCLEAR REACTIONS ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(t, \mathrm{p}\gamma ){}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$, $E\left(\mathrm{t}\right)=1.5-3.3\mathrm{}$ MeV, ${}_{}{}^3{}_{}{}^{}\mathrm{H}({}_{}{}^9{}_{}{}^{}\mathrm{Be}, \mathrm{p}\gamma ){}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$, $E\left({}_{}{}^9{}_{}{}^{}\mathrm{Be}\right)=10-16\mathrm{}$ MeV; measured DSA; deduced $\tau ({}_{}{}^{11}{}_{}{}^{}\mathrm{Be}, 320-\mathrm{k}\mathrm{e}\mathrm{V})$; calculated $B\left(E1\mathrm{}\right)\mathrm{}$, $B\left(M2\mathrm{}\right)\mathrm{}$ from thoery and compared to experiment for ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$.

• Received 18 April 1983

DOI:https://doi.org/10.1103/PhysRevC.28.497