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USNDP

9He (1988AJ01)


(See the Isobar Diagram for 9He)

9He has been observed in the 9Be(14C, 14O) reaction at E(14C) = 158 MeV (1987BEYI) and in the 9Be(π-, π+) reaction at Eπ- = 180 and 194 MeV (1987SE05): the atomic mass excesses are 41.5 ± 1.0 MeV and 40.80 ± 0.10 MeV, respectively. We adopt the latter value. 9He is then unstable with respect to decay into 8He + n by 1.13 MeV. (1987SE05) also report the population of excited states of 9He at 1.2, 3.8 and 7.0 MeV, while (1987BEYI) suggest an excited state at ≈ 1.8 MeV with Γ ≈ 3 MeV. Excited states are calculated at 1.64, 3.86 and 6.53 MeV, with Jπ = 1/2+, 5/2+ and 3/2- [(0 + 1)ℏω model space]. In the (0 + 2)ℏω model space the normal-parity excited states are at 6.44, 29.09 and 29.42 MeV with Jπ = 3/2-, 7/2-, 3/2-. In both cases the ground state is Jπ = 1/2-, as would be expected (1985PO10). See also (1984BE1C, 1988BEYJ), (1985AL1G, 1985SE1B, 1986FL1A, 1986FL1B, 1987HA1R, 1987PE1C, 1988SEZJ) and (1983ANZQ, 1984VA06, 1986AN07, 1987GI1C, 1987IK1B; theor.).