In the NUBASE2016 evaluation of nuclear properties (2017Au03), the ground state of ⁶H is listed as having a mass defect of 41880 keV 250, a half-life of 2.90×10^-22 s 70 and an estimated J^π of 2-. This corresponds to a resonance energy in the ³H+3n system of 2.72 MeV 25 and a resonance width of 1.57 MeV 38.

Calculations reported in (1985Po10,1989Go24) obtained the ⁶H ground state to have J^π=2-. However, a calculation reported in (1986Be02) gives J^π=1⁺ for the ground state.

Three particle transfer experiments, cited in the articles (1984Al08,1986Be35,2008Ca22), produced ⁶H in the final state and observed a resonance reasonably consistent with the NUBASE2016 evaluation. However, a pion double charge exchange reaction on ⁶Li, reported in (1990Pa25), which led to ⁶H in the final state, showed no sign of a ⁶H resonance. Also, experiments with stopped pions reported in (2003Gu17,2009Gu17) observed ⁶H resonances at higher excitation energies than the one given in the NUBASE2016 evaluation. Earlier experiments with stopped pions by the same group (1987Go25,1990Am04) saw no evidence of ⁶H states, but, as stated in (2003Gu17), that might have been due to poor statistics and energy resolution.

Theory:}

α shell model calculation with (0⁺1)h|w model space for ⁶H is reported in (1985Po10). From Fig. 1 in that article, the ground state energy of the p+5n system is about -3 MeV. From Table 1, the four lowest calculated states (using the ground state as E=0.0) are 0.0(2-),1.78(1-),2.80(0-),4.79(1⁺) MeV. These would correspond to resonant states in the ³H+3n system at approximately E(³H+3n)=5.5(2-),7.3(1-),8.3(0-),10.3(1⁺) MeV, taking into account the ³H binding energy of 8.5 MeV. In the same article, a shell model calculation with (0⁺2)h|w model space is also reported.

α shell model calculation for α=6 nuclei is reported in (1986Be02). For ⁶H, the calculated ground state has J^π=1⁺ and the binding energy is calculated to be 7.144 MeV in p+5n system which corresponds to a resonance at E=1.34 MeV in the ³H+3n system.

α calculation of H and He isotopes using the method of angular potential functions is reported in (1989Go24). For the ⁶H ground state, an energy of 6.3 MeV in ³H+3n system and J^π=2- were obtained.

α study of H and He isotopes using the anti-symmetrized molecular dynamics method is reported in (2004Ao05).

Positive experimental results: (See reaction data sets)}

Negative experimental results:}

⁹Be(π^-,pd)X,⁷Li(π^-,p)X:

1987Go25,1990Am04: Studies of the reactions ⁹Be(π^-,pd)X and ⁷Li(π^-,p)X with stopped pions were reported in (1987Go25,1990Am04). An analysis of the outgoing particle spectra showed no evidence of ⁶H states.

Note: The comment was made in (2003Gu17) that the failure to observe ⁶H states in either of the reactions reported in (1987Go25,1990Am04) may have been due to poor statistics and energy resolution.

⁶Li(π^-,π⁺)X:

1990Pa25: E(π^-)=220 MeV beam from the Los Alamos meson physics facility was incident on a ⁶LiH target and a missing mass π⁺ spectrum obtained. No evidence for ⁶H was found in the energy range -10 MeV to +30 MeV in the ³H+3n scale, thus casting doubt on the existence of ⁶H.

Also see (2007Fo05).