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¹⁰He has not been observed: see (74AJ01). The calculated mass excess of ¹⁰He is 53.34 MeV based on the modified form of the mass equation: ¹⁰He is then unstable with respect to breakup into ⁹He + n and ⁸He + 2n by 0.78 and 4.60 MeV (JE75). See also (VO73M, TH74) and (IR74A, BE75Q, IR76C, VA76L, KO78F, NA78E; theor.).