Observation of excited states in 5H

Structure of 10He low-lying states uncovered by correlations

The 0+ ground state of the 10He nucleus produced in the 3H(8He,p)10He reaction was found at about 2.1±0.2  MeV (Γ∼2  MeV) above the three-body ^{8}He+n+n breakup threshold. Angular correlations observed for ^{10}He decay products show prominent interference patterns allowing us to draw conclusions about the structure of low-energy excited states. We interpret the observed correlations as a coherent superposition of a broad 1- state having a maximum at energy 4-6 MeV and a 2+ state above 6 MeV, setting both on top of the 0+ state "tail." This anomalous level ordering indicates that the breakdown of the N=8 shell known in 12Be thus extends also to the ^{10}He system.

First observation of ground state dineutron decay: 16Be

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.