The neutron dripline at Z = 4: the case of $$^{13,15}\hbox {Be}$$ 13 , 15 Be

We review an extensive study of the beryllium isotopic chain carried out at RIKEN. In particular, we discuss the results on $$^{13,15}\hbox {Be}$$ , two key isotopes for the understanding of dineutron configurations and decays in $$^{14,16}\hbox {Be}$$ . In the $$^{13}$$ Be case, a detailed analysis of its spectroscopy, including for the first time a well-founded reaction framework and a realistic three-body model of $$^{14}\hbox {Be}$$ that incorporates core excitations, confirms the dominant $$\ell =1$$ content of the low-lying spectrum. In the $$^{15}$$ Be case, the fragmentation of $$^{18}$$ C, a priori free of any selection rules that may have precluded the observation of states in previous experiments, has confirmed the only known state at about 1.8 MeV, assigned according to shell-model calculations to a spin-parity $$5/2^+$$ . Some perspectives of these studies are also given.