Speaker
Description
$^{212}$Po has two protons and neutrons outside the doubly-magic nucleus $^{208}$Pb and it may be assumed that the nuclear structure can be well described within the shell model. But various experimental properties, such as the short-lived ground state, are better described by an $\alpha$-clustering model. The B(E2) values of the decays of low-lying yrast states are an important fingerprint to describe the structure of $^{212}$Po. Especially the missing B(E2; 4$_1^+ \rightarrow$ 2$^+_1$) value is important in this discussion. We have performed an $\alpha$-transfer experiment to investigate excited states of $^{212}$Po and determine the lifetimes using the ROSPHERE $\gamma$-ray detector array at IFIN-HH in Magurele, Romania. This array consisted of 15 HPGe detectors and 10 LaBr$_3$(Ce) scintillator detectors and was supplemented with the SORCERER particle-detector array. The combination of $\gamma$-ray and the particle detectors was an important tool to determining the mean lifetimes of all ground-state band levels up to the 8$^+$ state be applying the fast-timing method. I will present our lifetime analysis and discuss the results within the shell model and $\alpha$-clustering models. Supported by BMBF under Verbundprojekt 05P2021 (ErUM-FSP T07) via grant 05P21RDFN1
