Strong E1 transitions in ⁹Be, ¹¹Be, and ¹³C

The Doppler shift attenuation method has been used to make two measurements of the mean life of the ¹¹Be 320-keV level. The results are 150±30 fs from the ⁹Be(t, pγ)¹¹Be reaction and 168±17 fs from the ³H(⁹Be, pγ)¹¹Be reaction. The adopted value of 166±15 fs, from the present and previous measurements, corresponds to an extremely strong E1 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 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 transitions in ⁹Be and ¹³C.

NUCLEAR REACTIONS ⁹Be(t, pγ)¹¹Be, E(t)=1.5-3.3 MeV, ³H(⁹Be, pγ)¹¹Be, E(⁹Be)=10-16 MeV; measured DSA; deduced τ(¹¹Be, 320-keV); calculated B(E1), B(M2) from thoery and compared to experiment for ⁹Be, ¹¹Be, ¹³C.