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See also the A = 5 introductory discussion titled A = 5 resonance parameters.

The previous review (1988AJ01) noted that the ⁹Be(¹¹B, ¹⁵O) reaction at E(¹¹B) = 52 - 76 MeV showed no evidence for the formation of ⁵H (1986BE35, 1987BO40). For the earlier work see (1984AJ01). See also (1987KO47, 1988SEZJ). In several experiments on π^- absorption at rest there is some evidence for the formation of a very broad (8 ± 3 MeV) resonance in the ⁵H system with E_r = 7.4 ± 0.7 MeV in the ⁹Be(π^-, X) reaction [see (1987GO25) and the more recent work of (1991GO19, 1992AM1H)]. Measurements reported in (1990AM04, 1992AM1H) provide evidence for a state at E_r = 11.8 ± 0.7 MeV, Γ = 5.6 ± 0.9 MeV from ⁶Li(π^-, p) and a state at E_r = 9.1 ± 0.7 MeV, Γ = 7.4 ± 0.6 MeV from ⁷Li(π^-, d). In an experiment on ⁶Li(π^-, p) at E_π = 125 MeV (1980SE1A) a broad ⁵H state with E_r = 11.1 ± 1.5, Γ ≈ 14 MeV was observed. Evidence for a dineutron-containing breakup channel was reported in (1991SE06). Work on an experiment on ⁷Li(⁶Li, ⁸B)⁵H described in (1995ALZU) reported evidence for an unstable ⁵H nucleus at 5.2 ± 0.4 MeV above the ³H + 2n dissociation threshold. See also (1995AU04). A recent study of the ¹H(⁶He, 2p)⁵H reaction (1997KO07) reported a ⁵H resonance with decay energy into ³H + 2n of 1.1 ± 0.4 ± 0.3 MeV (0.3 MeV is the systematic error).

⁵H is calculated to have J^π = 1/2⁺, to be unstable with respect to two neutron emission and to have excited states at E_x = 2.44, 4.29 and 7.39 MeV with J^π = 5/2⁺, 3/2⁺ and 3/2⁺ [(0 + 1)ℏω model space], and at E_x = 2.85, 3.46 and 6.02 MeV with J^π = 3/2⁺, 5/2⁺ and 3/2⁺ [(0 + 2)ℏω model space] (1985PO10). A three-body calculation (2000SH23) predicts states in the ³H + n + n continuum with J^π = 1/2⁺, E_x = 2.5 - 3.0 MeV, Γ = 3 - 4 MeV; J^π = 3/2⁺, E_x = 6.4 - 6.9 MeV, Γ = 8 MeV; J^π = 5/2⁺, E_x = 4.6 - 5.0 MeV, Γ = 5 MeV. A calculation (2001DE02) with the generator-coordinate method using ³H + n + n three-cluster state predicts a ⁵H ground state energy E ≈ 3 MeV above the ³H + n + n threshold with Γ_n ≈ 1 - 4 MeV and a lifetime longer than the ⁴H lifetime. See also (1982SM09, 1983ANZQ, 1986BE44, 1987PE1C).