StrongE1transitions inBe9,Be11, andC13

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 ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$.