Enhanced Collectivity In Be-12

Electromagnetic quadrupole transition strength is a sensitive probe of the evolution of the structure of nuclei, particularly the competition between collectivity and magicity. We have performed a new lifetime measurement of the 2(1)(+) state of Be-12 to study the interplay of these phenomena. The lifetime was measured with the Doppler Shift Attenuation Method using the gamma-ray detector GRETINA. Excited states of Be-12 were produced via inelastic scattering at 55 MeV/nucleon, using several different targets to control for systematic uncertainties in the stopping powers. The lifetime is determined to be tau = 1.38 +/- 0.10(stat) +/- 0.19(sys) ps, which is about half the previously reported value at twice the precision. The reduced transition strength deduced from this result is B(E2;2(1)(+)-> 0(1)(+)) = 14.2 +/- 1.0(stat)+/- 2.0(sys) e(2) fm(4), which supports the quenching of the N = 8 shell gap in Be-12. (C) 2018 The Authors. Published by Elsevier B.V.