One-Quadrupole-Phonon States of Heavy Vibrational Nuclei Studied in Coulomb Excitation

One-quadrupole-phonon states of vibrational nuclei have been observed throughout the nuclear chart. Collective quadrupole excitations of symmetric and mixed-symmetric character allow for investigating the underlying microscopic nuclear structure as well as the effective proton-neutron interaction. Isovector valence-shell excitations are distinct especially near shell closures. The N = 80 isotones around the doubly-magic nucleus $^{132}$Sn and the region around the doubly-magic nucleus $^{208}$Pb are of particular interest. Projectile Coulomb-excitation experiments on the radioactive nucleus $^{142}$Sm and the stable nuclei $^{202,204}$Hg were performed in order to further our understanding of nuclear structure in these regions. The decay strength of the first excited state of $^{142}$Sm is determined to B(E2;2$^{+}$$_{1}$ -> 0$_{1,gs}$$^{+}$) = 32 (4) W.u. It is a foundation for the investigation of a possible restoration of shell stabilization in N = 80 isotones above the Z = 58 subshell closure. The 2$_{1,ms}$$^{+}$ state of $^{212}$ Po has recently been identified. The nucleus $^{204}$Hg is the particle-hole conjugate to $^{212}$Po with respect to the doubly-magic nucleus $^{208}$Pb. $^{204}$Hg was investigated together with its neighboring even-even isotope $^{202}$Hg for comparison to the situation in $^{212}$Po. One quadrupole-phonon mixed-symmetry states are identified in both nuclei, with transition strengths of B(M1;2$^{+}$$_{7}$ -> 2$_{1}$$^{+}$) = 0.16 (7) µ$_{N}$$^{2}$ in $^{202}$Hg and B(M1;2$_{2}$$^{+}$ -> 2$_{1}$$^{+}$) = 0.20 (2)µ$^{2}$$_{N}$ in $^{204}$Hg. This is the first time, that isovector valence-shell excitations have been identified in this mass region, using complete sets of decay strengths.