Orateur
Description
A large body of experimental evidence and many theoretical models assessing shape-coexistence in the neutron-deficient Pb region has been acquired [1]. The quadrupole deformed shapes are associated with different intrinsic configurations that intrude down to energies close to the spherical ground state, resulting in a unique shape-triplet in $^{186}$Pb [2,3]. In the shell-model picture, the intruder configurations are associated with 2p-2h and 4p-4h proton excitations across the Z=82 shell gap.
In this region, the onset of deformation along isotopic chains varies for different elements. For example, the onset of oblate deformation in Po isotopes starts surprisingly early [4]. Since the ground state in Pb isotopes is spherical, the onset of deformation can be assessed by investigating the excited 2$^+$ states associated with different shapes. In this talk, I will present our recent experimental program to shed light on this phenomenon. In particular, I will focus on simultaneous in-beam electron and $\gamma$-ray spectroscopy experiments employing the SAGE spectrometer [5] and lifetime experiments exploiting the APPA plunger device at JYFL, Finland.
[1] K. Heyde and J.L. Wood, Rev. Mod. Phys. 83, 1467 (2011).
[2] A.N. Andreyev et al., Nature 405, 430 (2000).
[3] J. Ojala et al., Commun. Phys. 5, 213 (2022).
[4] T.E. Cocolios et al., Phys. Rev. Lett. 106, 052503 (2011).
[5] J. Pakarinen et al., Eur. Phys. J. A 50: 53 (2014).
