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¹²Li is not observed in the 4.8 GeV proton bombardment of a uranium target: it is particle-unstable. The calculated value of its mass excess is 52.93 MeV [see (80AJ01)]: ¹²Li would then be unstable with respect to ¹¹Li + n, ¹⁰Li + 2n and ⁹Li + 3n by 3.92, 2.96 and 3.76 MeV, respectively. See also (80AJ01) and (KA82T, AN83D, VA84; theor.).