Extending the Southern Shore of the Island of Inversion to $^{28}$F

Revel A.,Sorlin O., Marques F. M.,Kondo Y., Kahlbow J., Nakamura T.,Orr N. A.,Nowacki F.,Tostevin J. A., Yuan C. X.,Achouri N. L.,Falou H. Al, Atar L.,Aumann T.,Baba H.,Boretzky K.,Caesar C., Calvet D., Chae H.,Chiga N.,Corsi A., Crawford H. L.,Delaunay F., Delbart A., Deshayes Q., Dombradi Z., Douma C. A., Elekes Z., Fallon P.,Gasparic I., Gheller J. -M., Gibelin J., Gillibert A.,Harakeh M. N., He W., Hirayama A., Hoffman C. R.,Holl M., Horvat A., Horvath A., Hwang J. W., Isobe T., Kalantar-Nayestanaki N., Kawase S.,Kim S., Kisamori K., Kobayashi T., Korper D., Koyama S., Kuti I.,Lapoux V., Lindberg S., Masuoka S.,Mayer J., Miki K.,Murakami T.,Najafi M., Nakano K., Nakatsuka N.,Nilsson T.,Obertelli A.,Santos F. de Oliveira,Otsu H., Ozaki T.,Panin V.,Paschalis S.,Rossi D., Saito A. T., Saito T., Sasano M.,Sato H.,Satou Y.,Scheit H., Schindler F., Schrock P., Shikata M., Shimizu Y., Simon H.,Sohler D., Stuhl L., Takeuchi S.,Tanaka M.,Thoennessen M., Tornqvist H.,Togano Y., Tomai T., Tscheuschner J., Tsubota J., Uesaka T.,Yang Z., Yasuda M., Yoneda K.

PHYSICAL REVIEW LETTERS（2020）

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摘要

Detailed spectroscopy of the neutron-unbound nucleus F-28 has been performed for the first time following proton/neutron removal from Ne-29/F-29 beams at energies around 230 MeV=nucleon. The invariant-mass spectra were reconstructed for both the F-27((*)) + n and F-26((*)) + 2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the F-28 ground state, with S-n(F-28) = -199(6) keV, while analysis of the 2n decay channel allowed a considerably improved S-n(F-27) = 1620(60) keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of F-28. Importantly, in the case of the ground state, the reconstructed F-27 + n momentum distribution following neutron removal from F-29 indicates that it arises mainly from the 1p(3/2) neutron intruder configuration. This demonstrates that the island of inversion around N = 20 includes F-28, and most probably F-29, and suggests that O-28 is not doubly magic.

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