Nuclear rotation in the continuum

Abstract

Background: Atomic nuclei often exhibit collective rotational-like behavior in highly excited states, well above the particle emission threshold. What determines the existence of collective motion in the continuum region, is not fully understood.Purpose: In this work, by studying the collective rotation of the positive-parity deformed configurations of the one-neutron halo nucleus 11 Be, we assess different mechanisms that stabilize collective behavior beyond the limits of particle stability.Method: To solve a particle-plus-core problem, we employ a non-adiabatic coupled-channel formalism and the Berggren single-particle ensemble, which explicitly contains bound states, narrow resonances, and the scattering continuum. We study the valence-neutron density in the intrinsic rotor frame to assess the validity of the adiabatic approach as the excitation energy increases.Results: We demonstrate that collective rotation of the ground band of 11 Be is stabilized by (i) the fact that the = 0 one-neutron decay channel is closed, and (ii) the angular momentum alignment, which increases the parentage of high-components at high spins; both effects act in concert to decrease decay widths of ground-state band members. This is not the case for higher-lying states of 11 Be, where the = 0 neutron-decay channel is open and often dominates. Conclusion:We demonstrate that long-lived collective states can exist at high excitation energy in weakly bound neutron drip-line nuclei such as 11 Be. Introduction. -Studies of exotic nuclei far from the valley of beta-stability reveal novel features, such as the formation of halo structures [1, 2], near-threshold clustering effects [3][4][5][6], and presence of new types of correlations [7]. In all these cases, the atomic nucleus exhibits properties characteristic of an open quantum system, whose properties are dramatically altered by the coupling to scattering and reaction channels [8].

Quest for superradiance in atomic nuclei

“…[38]. The resulting alpha (structural) spectroscopic factors range from 0.75 20 Ne confirm these high spectroscopic factors. The sd model space describes well another rotational band that is based on the 6.73 MeV 0 + state.…”

“…4 and in Fig. 3 we summarize some recent interesting results related to clustering in 20 Ne, see Ref. [18].…”

“…The survival of such states remains quite puzzling [19,20]. Examples of such broad states experimentally known in select light nuclei are shown in Fig.…”

“…In most cases, including the ground state, the cluster structure of 20 Ne appears to be unperturbed by an addition of an extra neutron. The first excited J π = 5/2 + state, however, is a notable exception, it is a mixed state combining L = 0 and L = 4 α + 16 O channels.…”

“…Consistency in observed overlaps and their large magnitude implies that the phenomenon is quite stable and cluster structure emerges already in a relatively small valence space. The 20 Ne nucleus is known to be strongly clustered. In Tab.…”