Low-spin and low-energy observables give access to the underlying nuclear structure of atomic nuclei. Moderately neutron-rich radioactive isotopes can efficiently be provided by the ($^{18}$O, $^{16}$O) two-neutron transfer reaction. The population of low-spin excited states allows measurements of their $\gamma$-ray coincidences and lifetimes, hence, electromagnetic matrix elements.
Improved microscopic understanding of cosmic nucleosynthesis calls for more precise and complete data on neutron-rich nuclei in the mass region around the doubly-magic nucleus $^{208}$Pb that serve to constrain microscopic nuclear models [1]. In particular, the $B(E2)$$\downarrow$ values of yrast transitions of $^{210}$Pb partially show discrepancies with shell-model calculations. However, the uncertainty of the adopted $B(E2; 2^+_1 \rightarrow 0^+_1)$ value [2] was too large to conclusively compare the experimental and theoretical results. Therefore, $^{210}$Pb was investigated in an experiment at the 10 MV FN-tandem accelerator at the University of Cologne.
Furthermore, the W, Os, Pt and Hg region of the nuclear chart exhibits phase transitions between oblate, prolate and spherical shapes [3, 4]. The energy ratio $R_{4/2} = E(4^+_1)/E(2^+_1)$ indicates a transition from $\gamma$-softness towards sphericity for the Pt isotopic chain when approaching the neutron-shell closure at $N = 126$. $^{200}$Pt with $N = 122$ could mark the transitional point between the $\gamma$-soft nuclei $^{196, 198}$Pt and the semi-magical, supposedly spherical $^{204}$Pt and was studied at the 9 MV tandem accelerator at the IFIN-HH in Bucharest-Măgurele. Besides the $R_{4/2}$ ratio, the $B_{4/2}$ ratio of the $B(E2)$$\downarrow$ values of the $4^+_1 \rightarrow 2^+_1$ and $2^+_1 \rightarrow 0^+_1$ transitions serves as a complementary indicator for nuclear structure.
The $B(E2)$$\downarrow$ value is inversely proportional to the lifetime of the de-exciting state. Therefore, we performed lifetime measurements applying the recoil-distance Doppler-shift method [5]. Our significantly more precise result for the $B(E2; 2^+_1 \rightarrow 0^+_1)$ value of $^{210}$Pb enhances the comparability to shell-model calculations, underlining a discrepancy in a consistent shell-model description of the $B(E2; 2^+_1 \rightarrow 0^+_1)$ and $B(E2; 4^+_1 \rightarrow 2^+_1)$ values [6]. Further, we measured the lifetimes of the $2^+_1$ and $4^+_1$ states of $^{200}$Pt allowing for the calculation of the $B_{4/2}$ ratio, which shows good agreement with the theoretical limit of a spherical nucleus, indicating the structural evolution within the Pt isotopic chain [7, 8].
[1] D. Kocheva et al., Eur. Phys. J. A 53, 175 (2017).
[2] C. Ellegaard et al., Nucl. Phys. A 162, 1 (1971).
[3] J. Jolie et al., Phys. Rev. C 68, 031301 (2003).
[4] E. Sahin et al., Phys. Lett. B 857, 138976 (2024).
[5] A. Dewald et al., Prog. Part. Nucl. Phys. 67, 786 (2012).
[6] C. M. Nickel et al., Phys. Rev. C 113, 014329 (2026).
[7] C. M. Nickel et al., Phys. Rev. C (2026, accepted).
[8] A. Esmaylzadeh et al., Nucl. Phys. A (2026, accepted).
*Supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) as part of the Project-ID No. 264883531 - Research Training Group 2128 'Accelence' and Project-ID No. 499256822 - Research Training Group 2891 'Nuclear Photonics' and by the German Federal Ministry of Education and Research (BMBF) under Grant No. 05P21RDCI2.
Dr
A. Blazhev
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
A. Coman
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Dr
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. Mitu
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Dr
A. Turturică
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Mr
A. Weber
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
C. Clisu-Stan
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Dr
C. Costache
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Dr
C. Fransen
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
C. Mihai
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
C.-D. Lakenbrink
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Mr
D. Bittner
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Dr
D. Kocheva
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
E. Kleis
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Dr
F. von Spee
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Prof.
G. Rainovski
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
Mr
H. Mayr
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Prof.
J. Jolie
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Dr
J. Wiederhold
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
K. Gladnishki
(Faculty of Physics, University of Sofia St. Kliment Ohridski, Sofia, Bulgaria)
Mrs
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)
Dr
M. Beckers
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
M. Boromiza
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Dr
M. Ley
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Prof.
N. Pietralla
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
N.M. Florea
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Prof.
N.M. Mărginean
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Dr
P.R. John
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
R. Kern
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
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)
Dr
R. Zidarova
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
R.E. Mihai
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
S. Pascu
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
S. Ujeniuc
(Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest-Măgurele, Romania)
Mr
T. Beck
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
T. Stetz
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Mr
U. Ahmed
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
Dr
V. Karayonchev
(Institute for Nuclear Physics, Universität zu Köln, Cologne, Germany)
Dr
V. Werner
(Institute for Nuclear Physics, Dept. of Physics, Technische Universität Darmstadt, Darmstadt, Germany)
