Nuclei are complex quantum objects due to complex nucleon-nucleon interactions. They can undergo rather rapid changes in structure as a function of nucleon number. A well known region of such a shape transition is the rare-earth region around N = 90, where accessible nuclei range from spherical nuclei at the closed neutron shell at N = 82 to deformed nuclei. For a better understanding of this phenomenon, it is of interest to study empirical signatures like the E2 transition strength B(E2;2₁⁺→0₁⁺) or the E0 excitation strength ρ²(E0;0₁⁺→0₂⁺). The nuclide ¹⁵²Gd with 88 neutrons is located close to the quantum phase transition at N = 90. The lifetime τ(0₂⁺) of ¹⁵²Gd has been measured using fast electronic scintillation timing (FEST) with an array of HPGe- and LaBr₃- detectors. Excited states of ¹⁵²Gd were populated via an (α,n)-reaction on a gold-backed ¹⁴⁹Sm target. The measured lifetime of τ(0₂⁺)=96(6)ps corresponds to a reduced transition strength of B(E2;0₂⁺→2₁⁺)=111(7) W.u. and an E0 transition strength of ρ²(E0) = 39(3) · 10⁻³ to the ground state. This result provides experimental support for the validity of a correlation between E0 and E2 strengths that is a novel indicator for a quantum phase transition. This work was published as J. Wiederhold et al., Phys. Rev. C 94, 044302 (2016).
