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Report No.

Level structures of $$^{56,58}$$Ca cast doubt on a doubly magic $$^{60}$$Ca

Chen, S.*; Browne, F.*; Doornenbal, P.*; Lee, J.*; Obertelli, A.*; Tsunoda, Yusuke*; Otsuka, Takaharu*; Chazono, Yoshiki*; Hagen, G.*; Holt, J. D.*; Jansen, G. R.*; Ogata, Kazuyuki*; Shimizu, Noritaka*; Utsuno, Yutaka   ; Yoshida, Kazuki   ; Achouri, N. L.*; Baba, Hidetada*; Calvet, D.*; Ch$^a$teau, F.*; Chiga, Nobuyuki*; Corsi, A.*; Cort$'e$s, M. L.*; Delbart, A.*; Gheller, J.-M.*; Giganon, A.*; Gillibert, A.*; Hilaire, C.*; Isobe, Tadaaki*; Kobayashi, Toshio*; Kubota, Yuki*; Lapoux, V.*; Liu, H. N.*; Motobayashi, Toru*; Murray, I.*; Otsu, Hideaki*; Panin, V.*; Paul, N.*; Rodriguez, W.*; Sakurai, Hiroyoshi*; Sasano, Masaki*; Steppenbeck, D.*; Stuhl, L.*; Sun, Y. L.*; Togano, Yasuhiro*; Uesaka, Tomohiro*; Wimmer, K.*; Yoneda, Kenichiro*; Aktas, O.*; Aumann, T.*; Chung, L. X.*; Flavigny, F.*; Franchoo, S.*; Gasparic, I.*; Gerst, R.-B.*; Gibelin, J.*; Hahn, K. I.*; Kim, D.*; Koiwai, Takuma*; Kondo, Yosuke*; Koseoglou, P.*; Lehr, C.*; Linh, B. D.*; Lokotko, T.*; MacCormick, M.*; Moschner, K.*; Nakamura, Takashi*; Park, S. Y.*; Rossi, D.*; Sahin, E.*; S$"o$derstr$"o$m, P.-A.*; Sohler, D.*; Takeuchi, Satoshi*; T$"o$rnqvist, H.*; Vaquero, V.*; Wagner, V.*; Wang, S.*; Werner, V.*; Xu, X.*; Yamada, Hiroki*; Yan, D.*; Yang, Z.*; Yasuda, Masahiro*; Zanetti, L.*

Gamma decays were observed in $$^{56}$$Ca and $$^{58}$$Ca following quasi-free one-proton knockout reactions from $$^{57,59}$$Sc. For $$^{56}$$Ca, a $$gamma$$ ray transition was measured to be 1456(12) keV, while for $$^{58}$$Ca an indication for a transition was observed at 1115(34) keV. Both transitions were tentatively assigned as the $$2^{+}_{1} rightarrow 0^{+}_{gs}$$ decays. A shell-model calculation in a wide model space with a marginally modified effective nucleon-nucleon interaction depicts excellent agreement with experiment for $$2^{+}_{1}$$ level energies, two-neutron separation energies, and reaction cross sections, corroborating the formation of a new nuclear shell above the N = 34 shell. Its constituents, the $$0_{f5/2}$$ and $$0_{g9/2}$$ orbitals, are almost degenerate. This degeneracy precludes the possibility for a doubly magic $$^{60}$$Ca and potentially drives the dripline of Ca isotopes to $$^{70}$$Ca or even beyond.



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