Information on mass chains and nuclides available on this website:

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²⁰C has not been observed in the 4.8 GeV proton irradiation of a uranium target (BO74A). The mass excess is predicted to be 37.17 MeV (TH74), 37.41 MeV (JA76M, WA76L). Assuming the mass excess of ²⁰C to be 37.3 MeV, ²⁰C is then stable with respect to ¹⁹C + n and ¹⁸C + 2n by 3.2 and 4.2 MeV, respectively [see ¹⁸C and ¹⁹C]. See also (TH72K) and (ST72F, BE75Q, BE76L; theor.).