engCederkall, J.Fahlander, C.Warr, N.Butler, P. A.Gaffney, L. P.Berry, T.Cox, D. M.Pakarinen, J.Kröll, Th.Henrich, C.Schilling, M.Stahl, C.Golubev, P.von Schmid, M.Rainovski, G.Berger, C.Berner, C.Gernhäuser, R.Illana, A.De Witte, H.Górska, M.Habermann, T.Saha, S.Knyazev, A.de Angelis, G.Borge, M. J. G.Tengblad, O.Otsuka, T.Tsunoda, Y.Iwanicki, J.Wrzosek-Lipska, K.Blazhev, A.Reiter, P.Rosiak, D.Seidlitz, M.First Measurement of the Quadrupole Moment of the $2_{1}^{+}$ State in $^{110}Sn $info:eu-repo/classification/ddc/530The Sn isotopic chain, exhibiting double shell closures at 100 Sn and 132 Sn , is a key testing ground for theoretical models of the atomic nucleus. It was originally predicted that the transitional matrix elements between the first 2+ state and the 0+ ground state for the even-even isotopes in this chain should show a simple dependence on the neutron number. This prediction was, however, disproven experimentally in some of the first experiments with postaccelerated radioactive beams, a situation that has remained unresolved ever since. Subsequent theoretical work has suggested that the explanation can be found in proton excitations across the 𝑍 =50 shell gap, with an accompanying experimental signature that the first excited 2+ state in 110 Sn should have a distinct oblate shape. In this Letter, we present the first measurements of the spectroscopic quadrupole moment of the 2+1 state, 𝐵⁡(𝐸⁢2;4+1→2+1) and 𝐵⁡(𝐸⁢2;4+2→2+1) values for 110 Sn , as well as the 𝐵⁡(𝐸⁢2;2+1→0+1) value with significantly improved precision compared to previous results. From the same experiment, half-lives of the 2+1 and 4+1 states were measured using the Doppler shift attenuation method. Our combined result, 𝑄⁡(2+1)=20⁢(8)  efm2 for 110 Sn , is the largest positive value known among the Sn isotopes, indicating an oblate shape of the state by more than 2⁢𝜎. Comparison of the 𝐸⁢2 transition strengths and quadrupole moments with recent shell model calculations are presented.Physical review letters 135(22), 222502 (2025). doi:10.1103/7ysn-8y1winfo:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionAPS2025info:eu-repo/semantics/openAccessDEhttps://repository.gsi.de/record/364066https://repository.gsi.de/search?p=id:%22GSI-2026-00246%22Researchersinfo:eu-repo/semantics/altIdentifier/doi/10.1103/7ysn-8y1winfo:eu-repo/semantics/altIdentifier/doi/10.15120/GSI-2026-00246info:eu-repo/semantics/altIdentifier/issn/0031-9007info:eu-repo/semantics/altIdentifier/wos/WOS:001629376700005info:eu-repo/semantics/altIdentifier/pmid/pmid:41385675info:eu-repo/semantics/altIdentifier/issn/1079-7114info:eu-repo/semantics/altIdentifier/issn/1092-0145info:eu-repo/grantAgreement/EC//101057511