Speaker
Description
The isotope $^{212}$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 standard shell-model. But various experimental properties, such as the short-lived ground state are inconsistent with this model and better predicted by an $\alpha$-clustering model. The B(E2) values of the decays of the low lying yrast-states are an important finger print to describe the structure of $^{212}$Po. Especially the missing B(E2; 4$_1^+ \rightarrow$ 2$^+_1$), and the corresponding missing lifetime of the 4$^+_1$ state, are important in this discussion.\
At the end of 2019, we had performed an experiment to determine the lifetime of the low-lying yrast states at the Bucharest FN Tandem accelerator in the Horia Hulubei National Institute for R\&D in Physics and Nuclear Engineering (IFIN-HH) in Magurele, Romania. $^{212}$Po were populated by an $\alpha$-transfer reaction between a $^{208}$Pb target and a stable $^{10}$B beam. The $\gamma$-rays from the excited states are detected at the ROSPHERE $\gamma$-ray detector array which consisted of 15 HPGe detectors and 10 LaBr$_3$(Ce) scintillator detectors. To detect coincidence particles, this setup was supplemented with the SORCERER particle detector system. The combination of $\gamma$-ray and the particle detectors was an important tool to determine the mean lifetimes of all ground state band levels up to the 8$^+$ state applying the fast-timing method.\
In this talk, I will present our lifetime analysis of the excited states of $^{212}$Po and will discuss the results within the shell-model and $\alpha$-clustering model.
