Modeling the electric dipole strength of neutron-rich ${}^8$He: Prediction of multineutron collective excitations

Abstract

We investigate the multineutron excitations of neutron-rich ${}^8$He in the electric dipole strength using a ${}^4$He+$n$+$n$+$n$+$n$ five-body model. Many-body unbound states of ${}^8$He are obtained in the complex scaling method. We found that the different excitation modes coexist in the dipole strength below the excitation energy of 20 MeV. The strength below 10 MeV comes from the ${}^7$He+$n$ channel, indicating the sequential breakup of ${}^8$He via the ${}^7$He resonance to ${}^6$He+$n$+$n$. Above 10 MeV, the strength is obtained from many-body continuum states with strong configuration mixings, suggesting a new collective motion of four neutrons with the dipole oscillation against ${}^4$He.

6 pages, 5 figures

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Cited by in corpus (7)

• Possible interpretation of the complex expectation values associated with resonances
• Structure of neutron-rich He $\Lambda$ hypernuclei using the cluster orbital shell model
• Soft dipole resonance in neutron-rich ${}^8$He
• Soft dipole resonance in ${}^8$C and its isospin symmetry with ${}^8$He
• Low-energy dipole strength in 8He
• Dipole response in deformed halo nuclei ${}^{42}\mathrm{Mg}$ and ${}^{44}\mathrm{Mg}$
• Physics of many-body resonances with complex scaling and applications to light unstable nuclei