New precision lifetime measurement of the $2_1^+$ state of $^{12}$Be

The $^{12}$Be nucleus exhibits a tension between two different nuclear structure effects: strong $\alpha$-clustering characteristics similar to $^{8,10}$Be, and a tendency towards spherical, single-particle behavior due to the canonically magic neutron number $N=8$. The observed drop of 1.2~MeV in its $2_1^+$ energy compared to $^{10}$Be suggests that the $N=8$ magic number breaks down in this nucleus, instead giving way to clustering. However, the previously determined $B(E2;2_1^+\rightarrow 0_1^+)$ strength lacks sufficient precision to ascertain whether $^{12}$Be is more elongated than $^{10}$Be, which is a critical test of the exact role of the valence neutrons. To resolve this issue, a new experiment has been performed using GRETINA with the Doppler shift attenuation method to determine the lifetime of the $2^+_1$ state with better than 10\% precision. Preliminary results from the analysis will be presented and the implications for the structure of $^{12}$Be will be discussed.