First observation ofα-cluster states in the14O + 4

Changbo Fu

¹

,

V. Z. Goldberg

²

,

G. V. Rogachev

³

et al.

Abstract

We measured 14 O + 4 He excitation functions for elastic scattering which demonstrate, for the first time, a well developed α-cluster structure in the proton rich nucleus, 18 Ne. We present the excitation energies and estimates of the spins for the dominant resonances using an R-matrix approach. A resonance at 9.2 MeV excitation energy in 18 Ne is particularly interesting. The spin-parity of the state is found to be 3 − and the α particle reduced width for the state appears to be comparable to the single particle limit. We have found indications for unusually large size of the observed α-cluster configuration. [2,3] have suggested that clustering remains in systems composed of a collection of α particles and valence nucleons. The available data on the α-cluster states in neutron rich nuclei are scarce [4][5][6][7], but they give indications for the developed cluster structures with very large moments of inertia. The study of non-self-conjugate nuclei has an advantage in that one can investigate isobaric analog states in mirror systems. Comparison of the results for both systems can bring new spectroscopic information and shed light on such properties as the radii of the cluster states. At present the data on the α-cluster states in proton rich nuclei are absent. There is no clear understanding of what will happen to cluster structure when valence protons are substituted for valence neutrons [3].α clustering may play a role in helium burning in astrophysical systems. Indeed, even if astrophysical reactions involving helium do not proceed through strong α-cluster states (because of high excitation energy), these states can provide an α width to the states that are closer to the region of astrophysical interest through configuration mixing [8]. For many systems, the information needed to understand this can be obtained only in the reactions induced by radioactive beams. This paper presents the first results on α-cluster states in 18

Invariant-mass spectroscopy of Ne18, O16 , and CCharity1, Brown2, Elson3 et al. 2019Phys. Rev. C222420View full textAdd to dashboardCite

“…A rather narrow level (Γ < 60 keV) is observed at 9.111(25) MeV and a higher-energy peak is also present at 11.58(64) MeV. The lower-energy peak was not observed in an α+ 14 O elastic scattering experiment, where an E * =9.2-MeV level was found, but its width is much larger (Γ=300 keV) [45]. The presence of the wider peak at almost the same energy may have reduced their sensitivity to the level we observed, but on the other hand with its small decay width, it may not have a strong α-cluster structure and thus was not strongly excited in the α-scattering experiment.…”

B10+αstates with chain-like structures inN14Kanada-En’yo1 2015Phys. Rev. C4110View full textAdd to dashboardCite

“…For cluster states having an α cluster around a core nucleus, well-known examples are 16 O+α states in 20 Ne and 12 C+α states in 16 O [6]. Recent experimental and theoretical studies have revealed many cluster resonances in highly excited states near the α-decay threshold also in unstable nuclei, for instance, A−4 He+α states in Be isotopes [1,4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], 10 Be+α states in 14 C [27][28][29][30]54], 14 C+α states in 18 O and their mirror states [31][32][33][34][35][36][37][38][39][40], 18 O+α states in 22 Ne [38]…”

Invariant-mass spectroscopy of $^{18}$Ne, $^{16}$O, and $^{10}$C excited states formed in neutron transfer reactions

“…A rather narrow level (Γ < 60 keV) is observed at 9.111 (25) MeV and a higherenergy peak is also present at 11.58(64) MeV. The lowerenergy peak was not observed in an α+ 14 O elastic scattering experiment, where a E * =9.2 MeV level was found, but its width is much larger (Γ=300 keV) [42]. The presence of the wider peak at almost the same energy may have reduced their sensitivity to the level we observed, but on the other hand with its small decay width, it may not have a strong α-cluster structure and thus was not strongly excited in the α-scattering experiment.…”