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We have studied the ground state of the unbound, very neutron-rich isotope of hydrogen H5, using the He6(d,He3)H5 reaction in inverse kinematics at a bombarding energy of E(He6)=55A MeV. The present results suggest a ground-state resonance energy ER=2.4±0.3 MeV above the H3+2n threshold, with an intrinsic width of Γ=5.3±0.4 MeV in the H5 system. Both the resonance energy and width are higher than those reported in some, but not all previous studies of H5. The previously unreported He6(d,t)Heg.s.5 reaction is observed in the same measurement, providing a check on the understanding of the response of the apparatus. The data are compared to expectations from direct two-neutron and dineutron decay. The possibility of excited states of H5 populated in this reaction is discussed using different calculations of the He6→H5+p spectroscopic overlaps from shell-model and ab initio nuclear-structure calculations.

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Physical Review C