17 Cederkall, J. Fahlander, C. Golubev, P. Knyazev, A. Iwanicki, J. Wrzosek-Lipska, K. Blazhev, A. Reiter, P. Rosiak, D. Seidlitz, M. Warr, N. Butler, P. A. Gaffney, L. P. Berry, T. Cox, D. M. Pakarinen, J. Kröll, Th. Henrich, C. Schilling, M. Stahl, C. von Schmid, M. Rainovski, G. Berger, C. Berner, C. Gernhäuser, R. Illana, A. De Witte, H. Górska, M. Habermann, T. Saha, S. de Angelis, G. Borge, M. J. G. Tengblad, O. Otsuka, T. Tsunoda, Y. KSP Physical review letters Physical review letters APS College Park, Md. 0031-9007 10.1103/7ysn-8y1w 222502 22 135 The 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. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. ; PUB:(DE-HGF)16, ; 0, ; WOS:001629376700005 Journal Article 2025 GSI-2026-00246 2025 pmid:41385675 https://repository.gsi.de/record/364066 https://doi.org/10.1103/7ysn-8y1w <Go to ISI>://WOS:001629376700005