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Isoscalar monopole excitations in $^{16}$O: $\alpha$-cluster states at low energy and mean-field-type states at higher energy

Abstract : Isoscalar monopole strength function in $^{16}$O up to $E_{x}\simeq40$ MeV is discussed. We found that the fine structures at the low energy region up to $E_{x} \simeq 16$ MeV in the experimental monopole strength function obtained by the $^{16}$O$(\alpha,\alpha^{\prime})$ reaction can be rather satisfactorily reproduced within the framework of the $4\alpha$ cluster model, while the gross three bump structures observed at the higher energy region ($16 \lesssim E_{x} \lesssim 40$ MeV) look likely to be approximately reconciled by the mean-field calculations such as RPA and QRPA. In this paper, it is emphasized that two different types of monopole excitations exist in $^{16}$O; one is the monopole excitation to cluster states which is dominant in the lower energy part ($E_{x} \lesssim 16$ MeV), and the other is the monopole excitation of the mean-field type such as one-particle one-hole ($1p1h$) which {is attributed} mainly to the higher energy part ($16 \lesssim E_{x} \lesssim 40$ MeV). It is found that this character of the monopole excitations originates from the fact that the ground state of $^{16}$O with the dominant doubly closed shell structure has a duality of the mean-field-type {as well as} $\alpha$-clustering {character}. This dual nature of the ground state seems to be a common feature in light nuclei.
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http://hal.in2p3.fr/in2p3-00638704
Contributor : Sophie Heurteau <>
Submitted on : Monday, November 7, 2011 - 4:05:05 PM
Last modification on : Wednesday, September 16, 2020 - 4:08:10 PM

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T. Yamada, Y. Funaki, T. Myo, H. Horiuchi, K. Ikeda, et al.. Isoscalar monopole excitations in $^{16}$O: $\alpha$-cluster states at low energy and mean-field-type states at higher energy. Physical Review C, American Physical Society, 2012, 85, pp.034315. ⟨10.1103/PhysRevC.85.034315⟩. ⟨in2p3-00638704⟩

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