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Low-lying structure of $$^{50}$$Ar and the $$N$$=32 subshell closure

Steppenbeck, D.*; Takeuchi, Satoshi*; Aoi, Nori*; Doornenbal, P.*; Matsushita, Masafumi*; Wang, H.*; Utsuno, Yutaka; Baba, Hidetada*; Go, Shintaro*; Lee, J.*; Matsui, Keishi*; Michimasa, Shinichiro*; Motobayashi, Toru*; Nishimura, Daiki*; Otsuka, Takaharu*; Sakurai, Hiroyoshi*; Shiga, Yoshiaki*; Shimizu, Noritaka*; S$"o$derstr$"o$m, P.-A.*; Sumikama, Toshiyuki*; Taniuchi, Ryo*; Valiente-Dob$'o$n, J. J.*; Yoneda, Kenichiro*

The neutron-rich nucleus $$^{50}$$Ar is produced by the fragmentation reactions of $$^{54}$$Ca, $$^{55}$$Sc, and $$^{56}$$Ti at the RIBF facility in RIKEN, and its deexcited $$gamma$$ rays are observed for the first time. The first $$2^+$$ level in $$^{50}$$Ar is identified to lie at 1178(18)keV from the most intense $$gamma$$-ray spectra. This experimental data, together with the systematics of the $$2^+$$ levels for surrounding nuclei, is analyzed with large-scale shell-model calculations. Consequently, the $$N=32$$ sub-shell gap in $$^{50}$$Ar is equivalent to that of $$^{52}$$Ca, thus making the $$2^+$$ level in $$^{50}$$Ar higher than that of $$^{48}$$Ar. The shell-model calculation also predicts that the $$N=34$$ sub-shell gap enhances in going from Ca to Ar, which will be verified by forthcoming experiments for $$^{52}$$Ar.



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Category:Physics, Multidisciplinary



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