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18O (1959AJ76)(See Energy Level Diagram for 18O) GENERAL: See also Table 18.1 [Table of Energy Levels] (in PDF or PS). Theory: See (1955EL1B, 1955RE1D, 1956TH1B, 1957RA1C, 1958RE1B).
Three resonances are reported, at Eα = 1.13, 1.79, and 2.33 MeV (1958GO69, 1958PH37): see Table 18.2 [Resonances in 14C(α, γ)18O] (in PDF or PS). Angular distribution measurements of the capture radiation at the resonances permit the assignments J = 0+, 2+, 4+ for the first three states of 18O and J = 4+, 1- and 1- to the resonance levels, 18O*(7.12, 7.64, 8.06) (1958GO69, 1958PH37). The branching ratios for the upper two levels do not agree with values estimated from a simple collective model (1958PH37). The ground state transition from 18O*(3.55) is less than 3% of the transition 3.55 → 1.98 (1958GO69).
Observed resonances in the 0° yield curve for Eα = 2.3 to 3.6 MeV are shown in Table 18.3 [Resonances in 14C(α, n)17O and 14C(α, α)14C] (in PDF or PS). The angular distribution of the neutrons at the 2.64 MeV resonance indicates J = 1- or 3- for the 8.29 MeV state of 18O (1956SA06).
Observed anomalies in the scattering for Eα = 2 to 3.9 MeV are shown in Table 18.3 [Resonances in 14C(α, n)17O and 14C(α, α)14C] (in PDF or PS). The resonances at Eα = (2.8), 3.3, and 3.5 MeV appear to have Γn >> Γα (1958WE29).
See (1951SU1A).
See (1956SH1A).
Not observed.
See (1953CU1D).
See (1949CH1A).
The thermal neutron cross section is 0.4 ± 0.1 b (1958HU18).
Proton groups have been observed corresponding to excited states at 1.986 ± 0.013 (1954AH37, 1954AH47: based on Q0), 1.981 ± 0.02 MeV, at 2.449 ± 0.02 MeV (1955HO28: based on Qm) and at 3.56 ± 0.02 MeV (1956BA1L: based on Q0). The reported level at 2.45 MeV is not found by (1956BA1L): an upper limit of 0.2 - 0.3 is given for the relative intensity of groups leading to states in the range Ex = 2 to 3.5 MeV compared to the ground-state group; see also 18O(p, p')18O* and 19F(t, α)18O. At Ed = 7.77 MeV, angular distributions of protons to the first three states of 18O are fitted by ln = 2, 0 and 2, respectively. Assignments of Jπ = 0+, 2+, 4+ are indicated for 18O*(0, 1.98, and 3.56 MeV). Derived coefficients for the first excited state wave function are in good agreement with the theories of (1954RE1B and 1955EL1B) (1957BI80).
See (1955AJ61) and (1955RE1C).
At Ep = 4.6 to 5.3 MeV, a group is reported corresponding to 18O*(1.981 ± 0.004). No evidence is found for a level at 2.45 MeV reported in 17O(d, p)18O: intensity less than 0.1 of 1.98 MeV group (1957YO04). A 1.9 MeV γ-ray is reported by (1956NA1C), presumably arising from the decay of the first excited state.
At Ed = 7.8 MeV, deuteron groups are reported to states at 0, 1.98 and 3.551 ± 0.019 MeV. Upper limits of 3 to 8 % are given for other possible groups in the range Ex = 2 to 3.5 MeV (1956BA1L). At Ed = 4.98 MeV, the Q = -1.98 MeV group is < 3% of the ground-sate group (1957YO04).
See 18F.
See 19F.
At En = 14.1 MeV, deuteron groups are observed to the ground state, to an excited state at 1.9 ± 0.1 MeV and , possibly, to others near 3 to 4 MeV. Angular distributions indicate lp = 0 for the ground state transition, consistent with J = 0+ or 1+, and most probably lp = 2 for the 1.9 MeV state (J = 1+, 2+, 3+). The ratio of reduced widths θ2p(1.9)/θ2p(0) = 0.87, in good agreement with shell model calculations of (1955EL1B and 1957RI44).
Not observed.
At Et = 1.8 MeV, α-groups are reported to levels at 1.989 ± 0.024, 3.504 ± 0.034, 3.929 ± 0.040, 5.007 ± 0.040, 5.170 ± 0.040, 5.311 ± 0.040, 5.456 ± 0.040, 6.190 ± 0.040 and 6.328 ± 0.040 MeV. No other states below Ex = 6.8 MeV are observed (1956JA31).
Not observed.
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