Speaker
Description
The generalised seniority scheme is a truncated version of the nuclear shell model [1]. It is able to describe the structure of atomic nuclei in the vicinity of shell closures. The number of unpaired nucleons, the seniority $\nu$, is considered a good quantum number.
The region of the even-even Po-Rn-Ra nuclei with $N=124$ exhibits strong signs of seniority-like behaviour. This can be observed, e.g. in the energy spacing between excited yrast states which decreases at higher angular momenta. However, no experimental data is available to confirm or falsify the anticipated parabolically increasing trend in the absolute $E2$ transition strength with the filling of the $j$-shell for the $\Delta\nu=2$ seniority-changing $2_1^+\to0_1^+$ transition [2]. Therefore, a Coulomb-excitation experiment was conducted at HIE-ISOLDE in 2024 in order to obtain the $B(E2; 2_1^+\to0_1^+)$ value of $^{212}$Ra. The $^{212}$Ra beam was impinged on a $^{120}$Sn target with $4.51\,$MeV/u to ensure safe Coulomb excitation. $\gamma$ rays of deexciting $^{212}$Ra nuclei were observed by the high-purity germanium detectors of the Miniball array [3] while ejectiles and recoiling particles were recorded by a double-sided silicon strip detector at forward angles. From the $\gamma$-ray yields the $E2$ strength of the $2_1^+\to0_1^+$ transition can be then deduced. The current state of the analysis will be presented.
[1] I. Talmi, Nucl. Phys. A 172, 1 (1971).
[2] J. J. Ressler et al., Phys. Rev. C 69, 034317 (2004).
[3] N. Warr et al., Eur. Phys. J. A 49, 40 (2013).
This work is financially supported by the German Federal Ministry of Education and Research (BMBF) under grant numbers 05P24RD3 and 05P24PKCI1, and the European Union's Horizon Europe research and innovation programme under grant agreement no. 101057511. DLB and AK were supported by the ELI-RO program funded by the Institute of Atomic Physics, Măgurele, Romania, contract number ELI-RO/RDI/2024-007 ELITE and the support of the Romanian Ministry of Research and Innovation under research contract PN 23 21 01 06. We thank the HIE-ISOLDE team for providing optimal beam conditions.
