Speaker
Description
The reduced transition probability or $B(E2;0^+_1\rightarrow 2^+_1)$ value and the spectroscopic quadrupole moment of the first excited 2$^{+}_{1}$ state, $Q_{_S}(2^{+}_{1})$, at 1.633 MeV in $^{20}$Ne have been determined at safe energies using the {\small TIGRESS} and AFRODITE arrays at TRIUMF and iThemba LABS, respectively. Large values of $B(E2;0^+_1\rightarrow 2^+_1)=22.4(16)$ W.u. and $Q_{s}(2^{+}_{1})=-0.26(3)$ eb present strong discrepancies when compared with mean-filed calculations and the collective model of Bohr and Mottelson. Modern relativistic mean-field calculations predict a dominant $^{16}$O$+\alpha$ configuration for the 2$^{+}_{1}$ state in $^{20}$Ne, which may explain current failures of collective and mean-field models, which underestimate the $Q_{s}(2^{+}_{1})$ value in $^{20}$Ne by about 30$\%$. These findings are relevant to understanding the mixing between mean-field and $\alpha$ cluster states and provide evidence for clustering formation in nuclei at low excitation energies below the $\alpha$ separation energy.
