Quadrupole collectivity near shell closures dominates the structure of low-lying excited states. The $B_{4/2}=\frac{B(E2;\, 4_1^+\to2_1^+)}{B(E2;\, 2_1^+\to0_1^+)}$ ratio as a measure of collectivity takes benchmark values in the collective limits of a spherical harmonic vibrator with $B_{4/2}^{\text{vib}}= 2$, or quadrupole-deformed limits with $B_{4/2}^{\text{rot}} = 1.43$, regardless of axial symmetry. For near-magic nuclei with seniority-dominated low-lying states, $B_{4/2}$ can take values even lower than unity. For $^{132}_{\phantom{1}52}$Te with its proximity to the $Z = 50$ and $N = 82$ shell closures this quantity will serve as an indicator of the balance between spherical-collective and spherical-seniority dominated structures.
The isoscalar proton-neutron symmetric $2_1^+$ state and the isovector mixed-symmetry $2^+_{\text{1,ms}}$ state are predominantly of one-quadrupole phonon character. Therefore, the properties of these states also give insights into the nuclear structure. The isotope $^{132}$Te is of particular interest since it is close to and an isobar of the doubly magic $^{132}$Sn. With only two valence protons and two valence-neutron holes, the mixing of the respective proton and neutron configurations into the wave functions is of utmost importance, as it constitutes the foundation for more complex collective states when turning to larger valence spaces.
Our recent lifetime measurements at IFIN-HH Bucharest [1] and IKP Cologne [2] on $^{132}$Te show emerging collectivity and complement the investigation of mixed-symmetry states in the $N=80$ isotonic chain. Here the $^{130}$Te($^{18}$O,$^{16}$O)$^{132}$Te two-neutron transfer reaction was employed to produce the radioactive $^{132}$Te. Shell model calculations have been performed to compare the contributions of different configurations to the wave function.
In a further study, $^{212}_{\phantom{2}88}$Ra is studied which is with $N=124$ in proximity to the neutron-shell closure at $N=126$. A radioactive $^{212}$Ra ion beam was provided by HIE-ISOLDE to explore the collectivity of its first excited $2^+$ state.
[1] T. Stetz, H. Mayr et al., Phys. Rev. C 112, 034325 (2025)
[2] H. Mayr, T. Stetz et al., Phys. Rev. C 113, 014318 (2026)
Supported by the BMFTR under grant numbers 05P21RDFN9, 05P21RDCI2 and 05P24RD3.
A. Blazhev
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
A. Esmaylzadeh
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
A. Ionescu
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
A. Pfeil
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
C. Costache
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
C. Mihai
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
C.R. Nita
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Clemens Nickel
(Institute for Nuclear Physics, Technische Universität Darmstadt)
D. Kocheva
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
E. Kleis
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
F. von Spee
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
G. Rainovski
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
H. Kleis
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
I. Dinescu
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
J. Fischer
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
K. Gladnishki
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
K.E. Ide
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
L. Stan
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
M. Beckers
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
M. Stoyanova
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
N. Pietralla
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
P. Koch
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
P. Koseoglou
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
R. Borcea
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
R. Lică
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
R. Mărginean
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
R. Zidarova
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
R.-B. Gerst
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
R.E. Mihai
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
S. Calinescu
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
S. Toma
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
T. Beck
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
T. Stetz
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Takaharu Otsuka
(Department of Physics, University of Tokyo)
V. Karayonchev
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
V. Werner
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Yusuke Tsunoda
(University of Tsukuba)
