RESUMO
Evidence for the ground state of the neutron-unbound nucleus (26)O was observed for the first time in the single proton-knockout reaction from a 82 MeV/u (27)F beam. Neutrons were measured in coincidence with (24)O fragments. (26)O was determined to be unbound by 150(-150)(+50) keV from the observation of low-energy neutrons. This result agrees with recent shell-model calculations based on microscopic two- and three-nucleon forces.
RESUMO
We report on the first observation of dineutron emission in the decay of 16Be. A single-proton knockout reaction from a 53 MeV/u 17B beam was used to populate the ground state of 16Be. 16Be is bound with respect to the emission of one neutron and unbound to two-neutron emission. The dineutron character of the decay is evidenced by a small emission angle between the two neutrons. The two-neutron separation energy of 16Be was measured to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.
RESUMO
The technique of invariant mass spectroscopy has been used to measure, for the first time, the ground state energy of neutron-unbound (28)F, determined to be a resonance in the (27)F+n continuum at 220(50) keV. States in (28)F were populated by the reactions of a 62 MeV/u (29)Ne beam impinging on a 288 mg/cm(2) beryllium target. The measured (28)F ground state energy is in good agreement with USDA/USDB shell model predictions, indicating that pf shell intruder configurations play only a small role in the ground state structure of (28)F and establishing a low-Z boundary of the island of inversion for N=19 isotones.