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.
Previously unknown isotopes30 Ar and 29 Cl have been identified by measurement of the trajectories of their in-flight decay products 28 S þ p þ p and 28 S þ p, respectively. The analysis of angular correlations of the fragments provided information on decay energies and the structure of the parent states. The ground states of 30 Ar and 29 Cl were found at 2.25 þ0.15 −0.10 and 1.8 AE 0.1 MeV above the two-and one-proton thresholds, respectively. The lowest states in 30 Ar and 29 Cl point to a violation of isobaric symmetry in the structure of these unbound nuclei. The two-proton decay has been identified in a transition region between simultaneous two-proton and sequential proton emissions from the 30 Ar ground state, which is characterized by an interplay of three-body and two-body decay mechanisms. The first hint of a fine structure of the two-proton decay of 30 Ar à ð2 þ Þ has been obtained by detecting two decay branches into the ground and first-excited states of the 28 S fragment.
appear in the even-proton number (Z) isotopes beyond the proton drip-line, in which one-proton (1p) emission is energetically prohibited but the ejection of two protons is energetically allowed due to the pairing interaction. More than 40 years after its prediction, ground-state 2p radioactivity was discovered in 2002 [2,3]. Two experiments independently observed that the ground state (g.s.) of 45 Fe decays by simultaneous emission of two protons. Later 54 Zn [4], 19 Mg [5], 48 Ni [6], and 67 Kr [7] were found to be other g.s. 2p radioactive nuclei. Among the g.s. 2p emitters hitherto observed, the halflives of 45 Fe, 48 Ni, and 54 Zn are in the range of several ms,
Structure with the lowest energy observed in the 10 He spectrum populated in the proton knockout reaction with a 11 Li beam has a peak at 1.2 to 1.5 MeV. This peak is usually interpreted as a resonant 0 + ground state of 10 He. Our theoretical calculations indicate that this peak is likely to be a superposition of 1 − , 0 + , and 2 + excitations with very similar shapes. Moreover, the "soft" 1 − excitation appears to be the lowest in energy. Such an anomalous continuum response is traced to the halo structure of 11 Li providing an extreme low energy shift to all the expected continuum excitations. Competition between effects on the spectrum of the initial-state structure and of the final-state interaction and three-body correlations in 10 He are discussed. The analogous effect of an extreme low-energy shift could also be expected in other cases of 2n emitters populated in reactions with halo nuclei. A simplified example of the 10 He spectrum in α knockout from 14 Be is given. We also discuss limits on the properties of 9 He stemming from the observed 10 He spectrum.
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