Background: Since the first experimental observation, two-nucleon radioactivity has gained renewed attention over the past fifteen years. The 6Be system is the lightest two-proton ground-state emitter, while 16Be has been 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 6Be and 16Be 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, is used to construct the three-body 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 5Li and 15Be, are employed in the calculations. Results: The ground state of 16Be 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 6Be shows a clear symmetry with respect to its mirror partner, the two-neutron halo 6He: 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 16Be and 6Be, the results are consistent with previous theoretical studies and confirm the dominant dinucleon configuration. This favors the picture of a correlated two-nucleon emission.
Date of publication:
Phys. Rev. C 97 (2018) 034613