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15O (1959AJ76)
(See the Energy Level Diagram for 15O)
GENERAL: See also Table 15.11 [Table of Energy Levels] (in PDF or PS).
Theory: See (1957TA1C, 1958FR1C).
Mass of 15O: The most precise determination of the mass difference 15O - 15N comes from 15N(p, n)15O, where (1958JO28) find Ethresh. = 3.7808 ± 0.0011 MeV: this value, with (n - 1H) = 0.783 MeV leads to 15O - 15N = 2.7595. Including the (p, n) value of (1955KI28) and the two 15O(β+)15N values of (1957KI22), one obtains a weighted mean of 15O - 15N = 2.7586 ± 0.0012, or 15O (mass excess) = 7.287 ± 0.005 MeV, 54 keV higher than the value of (1955WA1A).
| 1. 15O(β+)15N | Qm = 2.759 |
The maximum positon energy is 1.723 ± 0.005 MeV, 1.736 ± 0.010 MeV; the mean of these and two values from 15N(p, n)15O is 1.733 ± 0.005 MeV (1957KI22); an earlier report by (1950BR29) appears to be in error. The half-life is 123.4 ± 1.3 sec (1954KL36), 121 ± 3 sec (1955BA83), 120 ± 2 sec (1957KI22), 123.95 ± 0.50 sec (1957PE12): mean = 123.6 ± 0.45 sec. Log ft = 3.64. See also (1958BE1G; theor.).
| 2. 7Li(14N, 6He)15O | Qm = -2.706 |
See (1958AL1D).
| 3. (a) 10B(6Li, n)15O | Qm = 15.218 |
| (b) 10B(7Li, 2n)15O | Qm = 7.965 |
See (1957NO17).
| 4. (a) 12C(3He, p)14N | Qm = 4.772 | Eb = 12.071 |
| (b) 12C(3He, n)14O | Qm = -1.159 | |
| (c) 12C(3He, α)11C | Qm = 1.856 | |
| (d) 12C(3He, d)13N | Qm = -3.553 |
Resonances in the yields of reactions (a) and (b) are displayed in Table 15.12 [Resonances in 12C + 3He] (in PDF or PS) (1957BR18, 1958JO20). Differential cross sections and angular distributions have been determined to E(3He) = 5 MeV for the p0, p1 and p2 groups. At low energies, the distributions tend to be symmetric; at the higher energies they become more complex; they seem to conform neither to compound nucleus or stripping theory, and it must be concluded that features of both processes are present (1957BR18, 1958JO20). Consideration of the relative yields of the first four resonances lead to the tentative Jπ assignments given in the table (1957BR18). Neutron angular distributions have been determined in the range E(3He) = 1.89 to 2.51 MeV: they are asymmetric at the higher energies. The ratio of the cross sections of the (3He, n) and (3He, p1) reactions (both to the first T = 1 states of the A = 14 triad) has been determined at a number of energies for E(3He) = 1.8 to 2.6 MeV. The ratio approaches the theoretically predicted value of 2 at the higher energies. The ratio of the (3He, α0) to the (3He, n0) cross sections has been determined at two energies; the large cross section for the former suggests a direct interaction (1957BR18). The yields of 11C and 13N have been determined for E(3He) = 13 to 21 MeV by (1958CO1G). See also 11C, 14N and 14O.
| 5. 12C(α, n)15O | Qm = -8.507 |
| 6. 13C(3He, n)15O | Qm = 7.126 |
Not reported.
| 7. 14N(p, γ)15O | Qm = 7.300 |
Observed resonances are listed in Table 15.13 [Resonances from 14N(p, γ)15O] (in PDF or PS) (1951DU08, 1955BA83, 1956OV1A, 1957PIZZ). The cross section increases from (8.5 ± 3.7) × 10-12 b at 100 keV to (140 ± 30) × 10-12 b at 135 keV (1957LA13). Extrapolation of the 278 keV resonant yield and s-wave background from the broad 2600 keV resonance yields cross section values in good agreement with those of (1957LA13). Judging from 15N, one level near 7 MeV in 15O remains undiscovered (1957PIZZ); see 14N(p, p)14N.
At the 277 keV resonance (Ex = 7.56 MeV), capture gamma rays resulting from cascades through 15O states at 5.2, 6.1 and 6.7 MeV are observed, with partial radiative widths of 0.003 eV, 0.008 eV and 0.002 eV, respectively (± 25%). The direct ground state transition has not been observed: the relative intensity is less than 5% of the 6.10 MeV line (1955BA83: see also (1952JO1C)). Asymmetry (7 ± 3 %) in the ratio of 6.1 and 5.2 MeV γ-rays indicates that the 7.56 MeV state is not formed by s-waves. It is suggested that J = 5/2 (1955BA83). (1956OV1A, 1957PIZZ) find, on the other hand, that the 0.75 and 1.35 MeV γ-rays are isotropic and conclude that J = 1/2+: see 14N(p, p)14N. The transition (7.56 → 5.2) appears to involve 15O*(5.20) and not 15O*(5.25) (B. Povh and D. Hebbard, private communication). (It is not clear why the ground state decay (E1) should not occur.) The structure formerly attributed to a broad resonance at Ep = 0.7 MeV (1951DU08) is probably due to direct capture (see (1957HA03)). At the 1.06 MeV resonance (Ex = 8.28 MeV), transitions are observed through the 5.2 and 6.8 - 6.9 MeV states in addition to the direct ground state transition (1953LI1D). A p-γ correlation study indicates J = 3/2 for the 8.28 MeV state (1957GA1B, 1957GO1E, 1957GO1H, 1958GO46, 1958GO68).
| 8. 14N(p, n)14O | Qm = -5.930 | Eb = 7.300 |
| 9. (a) 14N(p, p)14N | Eb = 7.300 | |
| (b) 14N(p, p')14N* |
The yield of elastic protons, of inelastic protons and of 2.3 MeV γ-rays has been examined to Ep = 5.2 MeV: see Table 15.14 [Anomalies in 14N(p, p)14N and 14N(p, p'γ)14N] (in PDF or PS). The scattering anomalies are superposed on a background which decreases less rapidly than the Rutherford cross section; for Ep < 2.3 MeV, the background is largely s-wave, with some p-wave contribution above Ep = 1.5 MeV (see (1956BA1H, 1956TA16, 1957BO58, 1957HA03, 1958FE05, 1959FE71)). (1959FE1E) finds that two s-wave and one p-wave phase shifts are required to fit the non-resonant angular distributions above Ep = 1 MeV.
Data taken near the 277 keV resonance, 15O* = 7.56 MeV, at three angles, are consistent only with s-wave formation. The magnitude of the anomaly indicates J = 1/2+, Γ = 1.5 keV (1956OV1A, 1957PIZZ). The 1054 keV resonance, 15O* = 8.28 MeV, is also formed by s-waves, but the anomaly indicates J = 3/2+ (1957HA03: see, however, (1956TA16)). Calculation of level shifts suggests identification of these two states with 15N*(8.32, 8.57). The mirror of 15O*(6.79) is probably 15N*(7.31); 15O*(6.86) may correspond either to 15N*(7.16) or 15N*(7.57). In either case, one 15O level remains to be discovered in this region (1957PIZZ: see also (1957HA03)). The 1544 keV resonance is again s-wave, J = 1/2+. Assignments for the Ep = 1737 and 1799 keV resonances are not certain (1957HA03). The broad resonance at Ep = 2.3 MeV, 15O*(9.465), is s-wave, J = 1/2+ (1958FE05, 1959FE1E). It is suggested that the apparent breadth of this level reported in 14N(p, γ) may reflect some contribution from direct capture (1959FE1E).
Elastic scattering has also been studied at Ep = 9.8 MeV (1957HI56), at 14.5, 20 and 31.5 MeV (1956KI54) and at 20.0 MeV (1957CH32). See also (1957JA1B) and 14N.
| 10. 14N(p, d)13N | Qm = -8.324 | Eb = 7.300 |
| 11. 14N(p, α)11C | Qm = -2.916 | Eb = 7.300 |
Broad resonances in the yield of 11C are observed at Ep = 4.94, 5.3, 5.6 and 6.15 MeV, corresponding to 15O*(11.91, 12.3, 12.5, 13.04) (1952BL64: stacked foil method).
| 12. 14N(d, n)15O | Qm = 5.073 |
| Q0 = 5.15 ± 0.16 (1953EV03). | |
| Q0 = 5.13 ± 0.05 (1957NO1C). |
Neutron groups are listed in Table 15.15 [15O Levels from 14N(d, n)15O] (in PDF or PS), together with Jπ assignments obtained from stripping analysis of the angular distributions. Except for the ground state and the level(s) at 6.8 MeV, the fits to the theoretical distributions are not completely satisfactory, and the assignments must be treated with some reserve (1953EV03). See also (1956NO04, 1957NO1C). At Ed = 9 MeV, the ratio of the ground state reduced widths of 15N and 15O (from the maximum cross sections of the (d, p) and (d, n) reactions) is 1.71 (1956CA1D). Neutron thresholds have been observed at Ed = 1.24 ± 0.02, 1.967 ± 0.004 and 2.044 ± 0.004 MeV, corresponding to 15O*(6.15 ± 0.03, 6.792 ± 0.009, 6.860 ± 0.009) (1955MA85).
At Ed = 4.0 MeV, γ-radiation has been observed with Eγ = 6.81 ± 0.04, 6.12 ± 0.06 and 5.26 ± 0.04 MeV (the latter probably includes 14N(d, p)15N) (1955BE81: corrected for Doppler shift). Relative cross sections for the 14N(d, p)15N*(7.31) and 14N(d, n)15O*(6.81) γ-rays are given by (1955BE1G) for three energies. See also (1956FR1A; theor.) and 16O.
| 13. 14N(3He, d)15O | Qm = 1.806 |
Not reported.
| 14. 14N(α, t)15O | Qm = -12.513 |
Not reported.
| 15. 15N(p, n)15O | Qm = -3.542 |
| Ethresh. = 3.776 ± 0.008; | |
| Q0 = -3.539 ± 0.008 (1955KI28). | |
| Ethresh. = 3.7808 ± 0.0011; | |
| [Q0 = -3.5425 ± 0.0011] (1958JO28). |
| 16. 15N(3He, t)15O | Qm = -2.777 |
Not reported.
| 17. 16O(γ, n)15O | Qm = -15.655 |
See (1957SV1A).
| 18. 16O(n, 2n)15O | Qm = -15.655 |
See (1955AJ61).
| 19. 16O(p, d)15O | Qm = -13.428 |
Not reported.
| 20. 16O(d, t)15O | Qm = -9.396 |
Not reported.
| 21. 16O(3He, α)15O | Qm = 4.923 |
At E(3He) = 3 MeV, α-groups are observed corresponding to levels at Ex = 5.195 ± 0.01 and 5.247 ± 0.01 MeV. The separation is 52 ± 5 keV (1959PO61). From a similar experiment, excitations of 5.185 and 5.244 MeV are reported (K.W. Allen, R. Middleton and S. Hinds, private communication). See also (1952PO27, 1953KU08).
| 22. 17O(p, t)15O | Qm = -11.316 |
Not reported.