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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).

 1. 14C(α, γ)18O Qm = 6.243

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).

 2. 14C(α, n)17O Qm = -1.825 Eb = 6.243 Ethresh. = 2.340 ± 0.003; Q0 = -1.820 ± 0.002 (1956SA06).

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).

 3. 14C(α, α)14C Eb = 6.243

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).

 4. 14C(α, p)17N Qm = -9.75 Eb = 6.238

See (1951SU1A).

 5. 15N(t, p)17N Qm = -0.15 Eb = 15.842

See (1956SH1A).

 6. 15N(α, p)18O Qm = -3.971

Not observed.

 7. 16O(t, p)18O Qm = 3.730

See (1953CU1D).

 8. 17O(n, p)17N Qm = -7.93 Eb = 8.069

See (1949CH1A).

 9. 17O(n, α)14C Qm = 1.825 Eb = 8.069

The thermal neutron cross section is 0.4 ± 0.1 b (1958HU18).

 10. 17O(d, p)18O Qm = 5.842 Q0 = 5.821 ± 0.010 (1954AH37, 1954AH47).

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).

 11. 18O(γ, p)17N Qm = -15.99

See (1955AJ61) and (1955RE1C).

 12. 18O(p, p')18O*

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.

 13. 18O(d, d')18O*

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).

 14. 18F(β+)18O Qm = 1.667

See 18F.

 15. 19F(γ, p)18O Qm = -7.964

See 19F.

 16. 19F(n, d)18O Qm = -5.737 Q0 = -5.79 ± 0.08 (1957RI44).

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).

 17. 19F(d, 3He)18O Qm = -2.470

Not observed.

 18. 19F(t, α)18O Qm = 11.849

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).

 19. 21Ne(n, α)18O Qm = 0.704

Not observed.