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12O (1985AJ01)(See the Isobar Diagram for 12O) 12O has been observed in the 16O(α, 8He) reaction at Eα = 117.4 MeV (1978KE06) and in the 12C(π+, π-) reaction at Eπ = 164 MeV (1983BL08; see for angular distribution) and 180 MeV (1980BU15). The mass excess of 12O is 32.10 ± 0.12 MeV (1978KE06), 32.059 ± 0.048 MeV (1980BU15): we adopt 32.065 ± 0.045 MeV. 12O is thus unstable to decay into 10C + 2p by 1.79 MeV and into 11N* + p by 0.45 MeV [note that 11N* is probably not the ground state of 11N and that is very broad: see 11N]. The width of the ground state is ≈ 400 ± 250 keV. The diproton branching ratio of 12Og.s. is estimated to be 60 ± 30% (1978KE06). The d-coefficient in the IMME for A = 12 is calculated to be 0 ± 11 keV (1978KE06), 4.4 ± 7.2 keV (1980BU15). The first T = 2 state in 12N should occur at Ex = 12.29 ± 0.02 MeV (1978KE06). There is some indication of an excited state of 12O at Ex = 1.0 ± 0.1 MeV, which would imply an appreciable downward shift from the position of the analog first excited state in 12Be (1978KE06). See also (1980TR1E, 1981SEZR) and (1981WA1J, 1982NG01, 1983ANZQ; theor.).
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