Two-nucleon emitters within a pseudostate method: The case of Be6 and Be16

Abstract

Background: Since the first experimental observation, two-nucleon radioactivity has gained renewed attention over the past fifteen years. The 6 Be system is the lightest two-proton ground-state emitter, while 16 Be was recently proposed to be the first two-neutron ground-state emitter ever observed. A proper understanding of their properties and decay modes requires a reasonable description of the three-body continuum.Purpose: Study the ground-state properties of 6 Be and 16 Be within a general three-body model and investigate their nucleon-nucleon correlations in the continuum. Method:The pseudostate (PS) method in hyperspherical coordinates, using the analytical transformed harmonic oscillator (THO) basis for three-body systems, is used to construct the 6 Be and 16 Be ground-state wave functions. These resonances are approximated as a stable PS around the known two-nucleon separation energy. Effective core-N potentials, constrained by the available experimental information on the binary subsystems 5 Li and 15 Be, are employed in the calculations. Results:The ground state of 16 Be is found to present a strong dineutron configuration, with the valence neutrons occupying mostly an l = 2 state relative to the core. The results are consistent with previous R-matrix calculations for the actual continuum. The case of 6 Be shows a clear symmetry with respect to its mirror partner, the twoneutron halo 6 He: The diproton configuration is dominant, and the valence protons occupy an l = 1 orbit. Conclusions:The PS method is found to be a suitable tool in describing the properties of unbound core + N + N ground states. For both 16 Be and 6 Be, the results are consistent with previous theoretical studies and confirm the dominant dinucleon configuration. This favors the picture of a correlated two-nucleon emission.

Structure and decay of the extremely proton-rich nuclei O11,12

“…To describe the energy spectra and 2p decay of 11,12 O, we use the three-body core+nucleon+nucleon GCC approach [49,50]. The core ( 9,10 C) is chosen as a deformed rigid rotor.…”

“…This indicates that, besides diproton decay, there is another 2p decay mode -"democratic" decay -in the g.s. of 12 O, 11,12 O and their mirror systems. For 11 Li, the parameters of the core-nucleon potential are taken from Ref.…”

“…[31]. In order to benchmark the GCC model, we compare our calculations for 11 Li with those using the core-neutron potential of Ref. [60] (GCC in Fig.…”

“…The recent observation of the unbound nucleus 11 O [31] provides several unique opportunities in that regard. First, 11 O is a 2p emitter and the mirror to the 2n Borromean halo system 11 Li, which allows for the study of the Thomas-Ehrman effect in the extreme case involving proton-unbound and neutron halo systems.…”

Description of continuum structures in a discrete basis: Three-body resonances and two-nucleon decays

“…As shown in Ref. [17], this can be used to identify three-body resonances following the so-called stabilization method [18,19]. Examples on these two approaches will be shown in the following sections.…”