Highly excited states of 6He

Spectroscopy of Helium Isotope 6He

“…The level with E = 4.8 (2) MeV is observed for the first time and lies below the level with E = 5.5(3) MeV, which was observed in this region of excitations previously [3,4]. We have not received indications on the existence of the level with E =3.5(2) MeV, which was observed in reactions of stopped pion absorption by boron isotopes [9]. Perhaps this is due to the difference in the structures of the absorbing nuclei.…”

“…The rate of pion stopping in targets was about 6 × 10 4 s −1 . In one experimental run the measurements were carried out on the isotope-pure targets 9 Be and 12 C, targets 10 B (contribution of the 11 B impurity was 15%), 11 B (contribution of the 12 C impurity was 8%) and 14 C "radioactive" target (76% is 14 C, 23% is 12 C). The contribution of uncontrolled impurities in all targets was ≤ 1%.…”

Experimental observation of neutron-neutron correlations in nucleus 6He from 3H(alpha,p alpha)nn reaction

“…The excitation spectrum of the neutron-enriched 6 He nucleus, which manifests itself both as a threeparticle continuous spectrum, and as the formation of resonance states in this continuum, is quite difficult to study both experimentally and theoretically. If we analyze the investigations of the spectrum of the excitation of the 6 He nucleus in the energy gap between the energies of the decay thresholds (0.973 MeV< E < 12.203 MeV) on three (α + n + n) and two (t + t) particles, then the experimental results, as well as the theory of these studies, are quite controversial. There is no doubt only for the energy characteristics of the 2 + first excited state (E* = 1.797 MeV).…”

“…It should be noted that recent experiments with using the accelerated radioactive 8 He isotope beam [5], as well as the nuclear reactions caused by the interaction of pions with boron isotopes [6], allowed to obtain more information about the excitation spectrum of the 6 He nucleus.…”

“…The 6 He nucleus belongs to the so-called Borominian type nuclei with a two-neutron halo, in which any two-particle system is not bound. The reason why the two-body subsystems are unbound while the three-body system is bound is entirely due to the effective (in-medium) two-nucleon correlations.…”