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⁹He has been observed in the ⁹Be(π^-, π⁺)⁹He reaction at E_π^- = 194 MeV; the atomic mass excess is 40.81 ± 0.12 MeV. ⁹He is then unstable with respect to decay into ⁸He + n by 1.14 MeV (SE81I, NA80D, SE80, SE80D). See also (79AJ01) and (PO82A; hypernuclei) and (NG82; theor.).