A=12C (1968AJ02)

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¹²C (1968AJ02)

(See Energy Level Diagrams for ¹²C)

GENERAL: See also Table 12.7 [Table of Energy Levels] (in PDF or PS).

Shell model: (1956KU1A, 1956PE1A, 1957KU58, 1960ME1C, 1960TA1C, 1960WE1C, 1961BA1E, 1961TR1B, 1963NA04, 1963VI1A, 1964AM1D, 1964CL1A, 1964GI1B, 1964GI1C, 1964NE1E, 1965BA2E, 1965CO25, 1965FA1C, 1965NE1C, 1966GI1A, 1966HA18, 1966VA1D, 1966YO1B, 1967CO32, 1967EV1C, 1967KU1N, 1968HI1H).

Collective model: (1959BA1F, 1959BR1E, 1961CL10, 1962CL13, 1962GO1R, 1962WA17, 1963GO1Q, 1964BR1H, 1964VO1B, 1965ST22, 1965UB1B, 1965UB1A, 1965VO1A, 1966BO1X, 1966DA1F, 1966DR1F, 1966KR02, 1967BA2N, 1967BO1G, 1967BO04, 1967BR1E, 1967KR1C, 1967LA09, 1967LA1G, 1967PA10, 1967RI1B, 1967RO1G, 1967SA1K, 1967SO1A, 1967SO07, 1967BA1K, 1967BA12, 1967BA2D, 1968MI1E, 1968SO1B).

Cluster model: (1956GL1B, 1956PE1A, 1959PI1B, 1960BI1E, 1960IN1B, 1960SH1A, 1966HE1C, 1962MA1H, 1963MA1D, 1963MA1E, 1964GR1M, 1964MA1G, 1965BA2D, 1965BE1H, 1965FA1C, 1965IN1A, 1965KU1E, 1965NE1B, 1965SH11, 1966DA1J, 1966DU1D, 1966HA1R, 1966HE1C, 1966KA1A, 1966BR1U, 1967NO1C, 1967TA1C, 1967UI01, 1968GO01).

Special levels: (1959BA1D, 1960BA38, 1960WE1C, 1960ZE1B, 1961YO1A, 1962BA1C, 1963DU1C, 1963SE17, 1964LI1B, 1964NA1G, 1964PA1H, 1966BR2E, 1966ME05, 1966MO08, 1967RO1L).

E1 giant resonance: (1960SA1F, 1962NI1D, 1962VI01, 1963MI1B, 1963PE04, 1964GI1C, 1964MI1E, 1966DR1F, 1966LE1J, 1967BA2N, 1967DA1H, 1967DR1D, 1967KE1L, 1967ME1G, 1967MU1F, 1967YO04, 1968KA1M).

Special reactions: (1961BE1E, 1961JA1H, 1964AF1A, 1964DU1D, 1964PA1H, 1964RE1B, 1965KR1A, 1965MA1X, 1966DE1G, 1966DU1D, 1966PH1C, 1967AU1B, 1967KA1C, 1967ZI1A).

Transition probabilities: (1956EL1C, 1957KU58, 1962KU1D, 1962WA17, 1963BO1D, 1963KI1D, 1963KU03, 1963MA1E, 1964CL1D, 1965GR1H, 1965ST22, 1967HS1A, 1967KU1N).

Muon capture: (1965FO1F, 1965UB1A, 1966FR1J, 1967BA78, 1968BA2G).

Other topics: (1959CA1B, 1964RA1A, 1966BA42, 1966BO1P, 1966WI1E, 1966YO1C, 1967BL1D, 1967EL1E, 1967NE1G).

1. (a) ⁶Li(⁶Li, α)⁸Be Q_m = 20.808 E_b = 28.177
(b) ⁶Li(⁶Li, n)¹¹C Q_m = 9.457
(c) ⁶Li(⁶Li, p)¹¹B Q_m = 12.220
(d) ⁶Li(⁶Li, d)¹⁰B Q_m = 2.989
(e) ⁶Li(⁶Li, nα)⁷Be Q_m = 1.912
(f) ⁶Li(⁶Li, pα)⁷Li Q_m = 3.556
(g) ⁶Li(⁶Li, ⁶Li)⁶Li

Elastic scattering, studied for E(⁶Li) = 3.2 to 7.0 MeV follows the Mott formula at low energies, but deviates at energies ≳ 4.0 MeV. Angular distributions can be accounted for by the Blair cut-off model, but the parameters are not sharply defined (1966PI02).

For E(⁶Li) = 1.2 to 2.8 MeV, population ratios of ⁷Be*(0.43), ⁷Li*(0.48) and ¹⁰B*(0.72) remain approximately constant. Simple tunneling or compound nucleus models are not compatible with the data and a direct interaction through long-range tails is suggested (1962MC12). Absolute reaction cross sections at E(⁶Li) = 2.1 MeV are in reasonable agreement with estimates based on barrier penetration. A strong preference for α-emission suggests that the favored mechanism involves interacting clusters (1963HU02). A conspicuous feature of the α-spectrum involves a transition through highly excited states of ⁸Be, possibly those at E_x = 22.2 and 22.9 MeV with large ⁶Li + d parentage (1963KA20, 1964MA26). Angular distributions of α₀ and α₁ indicate stripping (1964MA26: 2.0 to 4.4 MeV). Noticeable fluctuations of protons angular distributions and of 0° α-yields in the range E(⁶Li) = 2.4 to 9.0 MeV (1966KI09), and 2.2 to 14.5 MeV (1967AL1F), indicate compound nucleus effects. See also (1962DE1F, 1963BA1Q, 1963CO35, 1963LE19, 1964CA1G, 1964GA1E, 1965NO1A), ⁸Be and ¹⁰B in (1966LA04), and ¹¹B and ¹¹C here.

2. ⁶Li(⁷Li, n)¹²C Q_m = 20.924

At E(⁷Li) = 2.6 MeV, population of the ¹²C states at 15.11 and 4.44 MeV is reported (1962BE24). See also (1957NO17, 1963KA1E).

3. ⁶Li(¹¹B, αn)¹²C Q_m = 12.260

See (1963HO1E).

4. ⁷Li(⁷Li, 2n)¹²C Q_m = 13.672

See (1962BE16, 1962BE24).

5. (a) ⁹Be(³He, γ)¹²C Q_m = 26.282 E_b = 26.282
(b) ⁹Be(³He, n)¹¹C Q_m = 7.562
(c) ⁹Be(³He, p)¹¹B Q_m = 10.325
(d) ⁹Be(³He, d)¹⁰B Q_m = 1.094
(e) ⁹Be(³He, t)⁹B Q_m = -1.087
(f) ⁹Be(³He, α)⁸Be Q_m = 18.913
(g) ⁹Be(³He, ³He)⁹Be

The yield of capture γ-rays to the ground and 4.4 MeV states (reaction (a)) has been measured for E(³He) = 2 to 4.5 MeV. The cross section increases monotonically; at 4.5 MeV, σ(γ₀) is ≈ 4 μb. A strong 17.6 MeV γ-ray is ascribed to reaction (f) (1964BL12). Evidence for decays via higher states of ¹²C is not conclusive (1963BL05, 1964BL12).

Excitation functions for neutrons (reaction (b)) have been determined by (1963DU12: 1.2 to 2.7 MeV; n₀, n₁, n₂, n₃, n₄₊₅; θ = 0° and 81.5°), (1965DI06: 1.3 to 4.9 MeV; n₀, n₁; θ = 0°, 90° and 160°), (1965TO06: 3.5 to 5.8 MeV; n₀, n₁, n₂₊₃, n₄₊₅, n₆, n₇, n₈; θ = 5° and 90°) and (1968OK1D: 3.5 to 9.9 MeV; n₀, n₁). See also (1959MA1D, 1962SE1A, 1966MA1R, 1967HA20). No sharp structure is observed but there is some suggestion from angular distribution data and excitation functions at forward angles for a broad structure (Γ ≈ 350 keV) at E(³He) ≈ 2 MeV: E_x = 27.8 MeV (1963DU12, 1965DI06). Comparison with (³He, p) shows reasonable similarity at low energies, but strong differences for E(³He) > 2.5 MeV (1965DI06, 1965TO06). For E(³He) = 3.5 to 5.8 MeV the reaction proceeds predominantly by direct interaction (1965TO06). The total cross section for ¹¹C production shows a broad maximum, σ = 113 mb, at E(³He) = 4.3 MeV (1966HA21: 3.2 to 10 MeV). See also (1965BR42, 1967HA20). Angular distributions of the polarization of neutrons to ¹¹C*(0, 2.0, 4.3 + 4.8) have been measured at nine ³He energies from 2.1 to 3.9 MeV by (1967TH1H). See also ¹¹C.

Excitation functions and angular distributions for protons (reaction (c)) have been measured for E(³He) = 1.0 to 2 MeV (1967CO03: 90°; p₂ to p₉), 1.8 to 4.9 MeV (1959WO53: total and differential cross sections; p₀ and p₁), 3 to 5 MeV (1959WO53: p₂ and p₃) and 5.7 to 10.2 MeV (1960HI08: 10°, p₀ to p₉; 90°, p₀, p₁). From E(³He) = 5.7 to 10 MeV the majority of angular distributions are essentially independent of energy, showing pronounced forward peaking, consistent with a predominantly direct process. The excitation curves show only a slow and smooth increase (1960HI08). See also ¹¹B.

Excitation functions for ground-state tritons (reaction (e)) for E(³He) = 2.4 to 4.1 MeV (θ = 20°, 40°, 55° and 90°) show a smooth rise with energy in the region explored (1960TA04). At θ = 20° the cross section then shows a broad maximum at E(³He) ≈ 4.5 MeV. Following this maximum, the cross section decreases to E(³He) ≈ 7.5 MeV and then rises slowly to 9 MeV. Angular distributions of ground-state tritons have been measured at 1 MeV intervals between E(³He) = 5.0 and 9.0 MeV (1967EA01). Near E(³He) = 10 MeV, excitation functions for tritons and deuterons show no detailed structure; angular distributions show characteristic direct interaction features. DWBA fits for tritons are less satisfactory than those for deuterons (1967CR04). See also (1960HI08).

The elastic scattering excitation function (reaction (g)) has been measured at 45° for E(³He) = 4.0 to 9.0 MeV: it decreases monotonically over this energy region (1967EA01). For reaction (f), see (1964BL12) and ⁸Be in (1966LA04).

6. ⁹Be(α, n)¹²C Q_m = 5.704

Neutron groups corresponding to ¹²C levels at 0, 4.4, 7.7, 9.6, (10.1) and (10.8) MeV are reported: see (1960AJ04, 1962NI02). Observation of the γ-decay of the 15.1 MeV level is reported by (1954RA35, 1957WA04, 1957WA1F). Angular distributions have been studied by (1959SM98: 1.9 to 2.7 MeV; n₀, n₁), (1960RE02: 2 to 5.6 MeV; n₀, n₁, n₂), (1960GA14: 3.35 and 5.10 MeV; n₁), (1963ME11: 5.3 MeV; n₁), (1960AJ04: 5.6 and 5.8 MeV; n₀, n₁, n₂), (1961GA03: 5.5, 5.8 and 6.0 MeV; n₀, n₁, n₂), (1967VE1D: 6 to 10 MeV; n₀, n₁, n₂), (1962KJ02, 1962KJ04, 1962NI02: 9.8 to 14.2 MeV; n₀, n₁, n₂, n₃₊₄), (1962DE1G, 1963DE27, 1965DE1F: 12.9 to 23 MeV; n₀, n₁) and (1963KO03: 17.5 to 22.1 MeV; n₀, n₁, n₃).

Doppler shift measurements on the transition ¹²C*(4.4 → g.s.) yield a mean life τ_m = 50 ± 6 fsec (1961DE38); 57⁺²³_-17 fsec, Γ_γ = (11.5⁺⁵_-3.2) meV (1966WA10); ≤ 48 ± 10 fsec (1967CA02): see Table 12.8 (in PDF or PS). The internal pair conversion coefficient indicates an E2 transition (1954MI68): the pair angular correlation permits M1 or E2 and favors the latter (1954HA07, 1956GO1K, 1956GO73, 1958AR1B). Angular distributions of n₁ and n₁-γ correlations strongly indicate a direct interaction mechanism even at E_α = 3.3 and 5.5 MeV (1960GA14, 1962KJ01). Gamma ray angular distributions have been studied by (1955TA28, 1959SM98, 1963SE04). See also ¹³C.

The 7.65 MeV state decays predominantly into ⁸Be + α (see reactions 15 and 28). The 7.7 MeV nuclear pairs have been observed: Γ_π/Γ = (6.6 ± 2.2) × 10^-6 (1959AL97, 1960AJ04, 1960AL04, 1961GA03). See also (1959AJ76) for a survey of the earlier work.

7. ⁹Be(⁷Li, ⁴H)¹²C

Not observed: see (1964CA05).

8. ¹⁰B(d, γ)¹²C Q_m = 25.188

At E_d = 0.95 MeV, the upper limit to the capture cross section is 0.1 μb (1955SA1B).

9. ¹⁰B(d, n)¹¹C Q_m = 6.468 E_b = 25.188

The thin-target excitation function in the forward direction in the range E_d = 0.3 to 4.6 MeV shows some indication of a broad resonance near E_d = 0.9 MeV. Above E_d = 2.4 MeV, the cross section increases rapidly to 210 mb/sr at 3.8 MeV, and then remains constant to 4.6 MeV (1954BU06, 1955MA76). The 0° excitation function for ground state neutrons shows no structure for E_d = 3.2 to 9.0 MeV. The angular distributions all show a sharp peak around 20° and a smaller contribution in the background direction. DWBA produces a satisfactory fit to these distributions, but the parameters vary with energy (1967DI01). Cross-section ratios have been obtained at E_d = 1 to 5 MeV for the neutrons and protons to the second, third, fourth, and fifth excited states of the ¹¹B and ¹¹C mirror nuclei (1967SC1K). Polarization measurements have been carried out for E_d = 2.5 to 4.0 MeV (1967ME1N). See also (1955SA1B) and ¹¹C.

10. ¹⁰B(d, p)¹¹B Q_m = 9.231 E_b = 25.188

Absolute yields and angular distributions are reported for various proton groups by (1952EN19, 1954BU06, 1954PA28, 1956MA69, 1956VA17, 1959CR1A, 1960CR1A, 1960HA08, 1964BR1A, 1965LE1B, 1967PO01) for E_d = 0.14 to 12 MeV. Although the excitation functions show several broad peaks, no clear resonances can be identified, and it is assumed that many overlapping resonances are involved (1956MA69) except possibly at E_d = 2.3 MeV (E_x = 27.1 MeV) where the effect of a broad resonance influences the cross section of the p₁ and p₃ groups (to ¹¹B*(2.14, 5.03)) (1964BR1A). Studies of plane wave, distorted wave and Coulomb wave Born approximation angular distributions are reported by (1967PO01: see also (1966MO1H, 1967MO1N). There are no significant fluctuations in the yield of protons for E_d = 5 to 12 MeV (1965LE1B: θ = 50° and 150°). See also (1965BA31). Yields of gamma rays have been measured by (1955SA1B). Cross section ratios for the (d, n) and (d, p) reactions to mirror states have been measured by (1967SC1K) [see reaction 9].

Polarization measurements have been made by (1959HI1E: 6.9 MeV; p₀), (1964BE08: 10 MeV; p₀, p₁, p₂ + p₃), (1962TA13, 1964PA1E: 11 to 13.8 MeV; p₀), (1960TA27: 11.4 MeV; p₀), (1963BO1J: 21 MeV; p₀). The circular polarization of 2.12 and 4.44 MeV γ-rays has been investigated at E_d = 0.45 MeV (1960ER1A, 1961ZI02, 1962ZI01, 1963ER1A). See also ¹¹B.

11. ¹⁰B(d, d)¹⁰B E_b = 25.188

See ¹⁰B and (1965LE1B, 1967DI01, 1967PO01).

12. ¹⁰B(d, α)⁸Be Q_m = 17.819 E_b = 25.188

Excitation curves and angular distributions are reported for α₀ and α₁ groups (to ⁸Be*(0, 2.9)) by (1956MA69, 1960BE15, 1961LE10, 1963PU02, 1964AL1Q, 1964BR1A, 1966LO18, 1967LO1J) for E_d = 0.4 to 3.3 MeV. Broad maxima are observed in both excitation curves above E_d = 1 MeV. Preliminary data at E_d = 0.98 MeV indicate the formation of a level in ¹²C at 26.00 ± 0.01 MeV which decays via ⁸Be*(2.9) and ⁸Be_g.s. (1967PE1B).

13. ¹⁰B(d, ⁶Li)⁶Li Q_m = -2.989

This reaction has been studied for E_d = 8 to 13.5 MeV. A DWBA calculation with L = 2 α-transfer gives a qualitative account of the angular distribution (1964GE10).

14. ¹⁰B(t, n)¹²C Q_m = 18.931

Not reported.

15. ¹⁰B(³He, p)¹²C Q_m = 19.695
Q₀ = 19.6945 ± 0.0036 (1967OD01).

Proton groups observed by (1958MO99, 1959AL96, 1962BR10, 1967CO1F) are displayed in Table 12.9 (in PDF or PS). Angular distributions of many of these groups have been measured for E(³He) = 2.0 to 3.0 MeV (1965BH1A), 3.7 MeV (1962BR10), 10.1 MeV (1962AL01) and 14 MeV (1967CO1F). The following comments on individual levels derive largely from the ¹⁰B(³He, p)⁴He⁴He⁴He studies of (1964ET02, 1965AL1B, 1966WA16): see Table 12.9 (in PDF or PS).

¹²C*(7.65, 9.6) are observed to decay to ⁸Be_g.s., confirming natural parity π = (-1)^J for both states (1966WA16). Pair emission from ¹²C*(7.66) has been measured: Γ_π/Γ = (6.6 ± 2.2) × 10^-6 [see Table 12.8 (in PDF or PS)] as has the cascade through ¹²C*(4.4): Γ_γ/Γ = (3.3 ± 0.9) × 10^-4 (1961AL23). By observation of ¹²C recoils, a value Γ_rad/Γ = (3.5 ± 1.2) × 10^-4 is found by (1964HA23): compare to ¹⁴N(d, α)¹²C.

¹²C*(10.8) decays to both ⁸Be*(0, 2.9), indicating natural parity. (1966WA1C) searched for ¹²C*(10.1) with inconclusive results: see also (1962BR10).

¹²C*(11.83, 12.71, 13.35) decay to ⁸Be*(2.9) but not to the g.s., indicating unnatural parity: this result is inconsistant with the assignment (1^-) to ¹²C*(11.83): see (1964BR25). For ¹²C*(12.71) Γ_γ/Γ_α = (3 ± 1)% (1958MO99), (2 ± 1)% (1959AL96): the cascade through ¹²C*(4.4) is (20 ± 7)% relative to the ground-state transition (1960AL14): see Table 12.9 (in PDF or PS). The alpha breakup of ¹²C*(12.71) shows a triple-peaked α-particle spectrum, characteristic of the breakup of a J^π = 1⁺ state (1967BH1B).

¹²C*(14.08) decays both to ⁸Be*(0, 2.9); the branching ratio Γ(α₀)/Γ is 0.1 - 0.4. Proton α-correlations require J ≥ 2 (1966WA16).

¹²C*(15.11: J^π = 1⁺; T = 1) decays by γ-emission to ¹²C_g.s. 97% and to ¹²C*(4.4) (3.1 ± 0.6)% (1959AL96), (4 ± 1)% (1960AL14); Γ_α/Γ < 0.2 (1960MI1E), < 0.05 (1965AL1B), < 0.10 (1966WA16), respectively. The strong inhibition of the transition to ⁸Be*(2.9) is cited as evidence for a high isospin purity (1965AL1B): see, however, (1958KA31).

¹²C*(16.11, 16.57) show decay to both ⁸Be*(0, 2.9). The consequent assignment of natural parity is consistent with J^π = 2⁺ for the former but not with the accepted J^π = 2^- for the latter [see reaction 19]. For ¹²C*(16.11) observed values of Γ_α₀/Γ are 0.05 - 0.12; the decay to 3α occurs rarely, if at all (1966WA16: see, however, ¹¹B(p, α)⁸Be: (1965DE1R)).

The giant resonance excitation region has been searched for levels with a resolution of ≈ 20 keV at E(³He) = 14 MeV. Two peaks have been observed corresponding to ¹²C* ≈ 20.6 and 24.5 MeV, with Γ ≈ 200 and 50 keV, respectively. Angular distributions show forward maxima. peaks which could be associated with structure seen in photodisintigration experiments are not observed (1967CO1F). See also (1959JO1E, 1961AL10, 1961WO08, 1962KU02, 1965SI05, 1966BA01) and ¹³N.

16. ¹⁰B(α, d)¹²C Q_m = 1.341
Q₀ = 1.3406 ± 0.0015 (1965BR28).

At E_α = 21.2, 23.0 and 25.0 MeV angular distributions of the deuterons corresponding to ¹²C*(0, 4.4) have been measured (1967AL16).

See also (1959HE1C, 1960ON01, 1965JA03, 1965NI1B) and ¹⁴N.

17. ¹⁰B(⁶Li, α)¹²C Q_m = 23.716

At E(⁶Li)_c.m. = 3.05 MeV, angular distributions have been obtained for α₀, α₁, α₂ and α₃. The α-particles to ¹²C*(11.83) and (12.71) have also been observed (1966MC05). At E(⁶Li) = 3.8 MeV, the population of the T = 15.11 MeV state is about 3 ± 2% of the T = 0 state at 12.71 MeV. It is pointed out that in this reaction the distance of closest approach is 15 fm and the dominant potential would be the Coulomb potential. It is therefore not neccessary to invoke a large T = 0 mixing in the 15.11 MeV state to explain the observation of the 15 MeV γ rays (1964CA18).

See also (1963MI02, 1963MO1B, 1965GA1H, 1966BR1G, 1967SE08).

18. ¹⁰B(⁷Li, αn)¹²C Q_m = 16.463

See (1964CA18).

19. (a) ¹¹B(p, γ)¹²C Q_m = 15.957
(b) ¹¹B(p, α)⁸Be Q_m = 8.588 E_b = 15.957

In the range E_p = 0 to 25 MeV, twenty-three resonances are reported. Their characteristics are displayed in Table 12.10 (in PDF or PS). Cross sections of astrophysical interest are discussed by (1967FO1B).

The E_p = 0.16 MeV resonance (¹²C* = 16.11 MeV) is well established as the J^π = 2⁺; T = 1 analogue of the first excited states of ¹²B and ¹²N: see (1959AJ76). The resonant energy is 163.1 ± 0.2 keV; Γ_lab = 6.5 ± 0.6 keV [see (1955AJ61)]. The gamma decay of the 16.11 MeV state takes place to ¹²C*(0, 4.4, 9.6): see (1959AJ76, 1961CA13, 1961SE10). The decay to ¹²C*(9.6) is via a 6.45 ± 0.05 MeV γ-ray whose angular distribution, together with the known α-decay properties of ¹²C*(9.6), leads to J^π = 3^-. The intensity of the transition is 1% of the γ₁ decay (1961CA13). See also (1961GR07, 1965CV1A, 1966SO1B).

The character of the α-decay at the E_p = 0.16 MeV resonance has been studied with coincidence techniques by (1961DE31, 1962DE1H, 1964DE1J, 1965DE1R). Immediately below and above the resonance, a Dalitz plot indicates sequential decay via ⁸Be*(0, 2.9): in this region, the behavior is ascribed to tails of the E_p = 0.675 and 1.4 MeV resonances. At E_p = 0.163 MeV, the Dalitz plot shows a striking increase in population near the center, indicative of direct 3α breakup. Some part of the reaction also goes through ⁸Be_g.s., and there is evidence for a final-state two-body interaction with l = 2 (1964DE1J): see, however, (1965MA1X, 1965PH1A, 1966CH1L, 1966WA16). See also (1959KA12, 1959KA13, 1960BO26, 1962BE21, 1964DE1H, 1964LO05, 1964LO1E, 1965KR1A, 1965KR1B, 1967KA09, 1967LO1H). Similar studies at E_p = 0.675, 1.388 (1965KA1G), 2.0, 2.65, 3.25, 3.73, 4.00, 5.08, and 5.64 MeV (1964PH1A, 1965BR18, 1965PH1A) indicate that sequential decays through ⁸Be*(0, 2.9) dominate; direct 3α decay is < 5%. The latter work shows evidence for "order-of-emission" interference in the shapes of α-groups: see also (1965DU1C, 1965SW1B). See also (1958FO1D, 1966AD1E, 1966SO1B, 1967LO1H, 1968CH1L).

The E_p = 0.67 MeV state (¹²C* = 16.58 MeV) has a proton width Γ_p ≈ 150 keV. Such a width indicates s-wave protons and therefore J^π = 1^- or 2^-. These assignments are supported by the near isotropy of the two resonant exit channels, α₁ and γ₁. The size of the α₁ cross section indicates 2J + 1 ≥ 5; therefore J^π = 2^-. The reduced width θ²(α₁) ≈ 0.05 and the γ₁ E1 transition has |M|² ≈ 0.01 Weisskopf units, suggesting T = 1 (1957DE11, 1965SE06). See also (1959AJ76). (1962BL10) report a γ-branch to the 12.71 MeV state, ≈ 6% of the intensity of the 4.4 MeV transition. Such a branch may also be present at ¹²C*(17.23).

For the E_p = 1.4 MeV state (¹²C* = 17.23 MeV), (2J + 1)Γ_γ₀ ≥ 115 eV. This indicates J^π = 1^-, with T = 1 most probable (1965SE06). J^π = 1^- is also required to account for the interference at lower energies in α₀ and γ₀: see (1957DE11); see also (1959AJ76). Two solutions for Γ_p are possible; the larger (chosen for Table 12.10 (in PDF or PS)) is favored by elastic scattering data (1965SE06). (1963SY01) find no evidence for resonance in α₀ or α₁ at this energy.

J^π = 0⁺; T = 1 is consistent with all data for the E_p = 2.0 MeV resonance (¹²C* = 17.77 MeV) which decays via the α₀ and α₁ channels (1965SE06). The resonance in the yield of α₀ requires natural parity, and the small α-widths suggest T = 1. For J^π = 1^- or 3^- the small γ-widths would be surprising; J^π = 2⁺ would lead to a larger elastic anomaly than is observed (1965SE06: see also (1963SY01)).

At E_p = 2.62 MeV (E_x = 18.36 MeV), the resonance for α₀ again demands natural parity; the presence of a large P₄ term in the angular distribution requires J ≥ 2 and l_p ≥ 2. The assignment J^π = 3^-; T = 0 is consistent with the resonance data and with the angular distribution of α₀ at the E_p = 1.98 MeV resonance (1965SE06: see also (1955GO10, 1963SY01, 1967FL1F, 1968CH1L)).

The E_p = 2.66 MeV resonance, distinguished from that at E_p = 2.62 MeV by its width, is not seen here: see ¹¹B(p, p).

The E_p = 3.01 MeV resonance appears only in the angular distributions for α₀: the small α-widths suggest T = 1 (1965SE06).

At E_p = 3.12 MeV (E_x = 18.82 MeV), the angular distribution of γ₀ indicate E2 radiation, J^π = 2⁺. This assignment is supported by the angular correlation in the cascade γ₁ and by the behavior of σ( α₀); T = 1 is suggested by the small Γ_α (1965SE06).

The structure near E_p = 3.5 - 3.7 MeV (E_x = 19.2 and 19.4 MeV) seems to require at least two levels. The large Γ_γ₀ requires that one be J^π = 1^-; T = 1 and interference terms in σ(α₀) require the other to have even spin and even parity: J^π = 2⁺; T = 0 is favored (1963SY01, 1965SE06).

Levels at E_p = 4.93 and 5.11 MeV, seen in σ(γ₁) (1955BA22) also appear in σ(α₁), but not in σ(α₀). Angular distributions suggest J^π = 2⁺ or 3^- for the latter (E_x = 20.64 MeV); the strength of γ₁ and absence of γ₀ favors J^π = 3^-; T = 1 (1963SY01).

In the range 4 < E_p < 14.5 MeV, σ(γ₀) is dominated by the giant dipole resonance at E_p = 7.2 MeV (E_x = 22.6 MeV), Γ_cm = 3.2 MeV: ∫ σdE = 630 eV · b. σ(γ₁) likewise shows a giant resonance centered at about 10.3 MeV (E_x = 25.4 MeV), Γ_cm ≈ 6.5 MeV, ∫ σdE = 850 eV · b. Both excitation functions show significant fine structure (Table 12.10 (in PDF or PS)): see (1964AL20, 1967FE04).

From E_p = 4 to 14 MeV the angular distributions of γ₀ are given by W(θ) = 1 + a₁P₁(cosθ) + a₂P₂(cosθ) with the coefficient a₂ almost constant at -0.6, in approximate agreement with the expectation from particle-hole calculations of J^π = 1^-; T = 1 states by (1962VI01). The a₁ term exhibits fluctuations for E_p = 4 to 5.5 MeV in the region of narrow resonances; from 5.5 to 14 MeV it rises smoothly from +0.03 to +0.3. A sharp resonance in σ(γ₁) at E_p = 10.15 MeV, ∫ σdE = 4 eV · b, may have T = 2 (1964AL20). See also (1959GE33, 1959GO89, 1961GO13, 1963BE18, 1964AL1J, 1964BL1D, 1964TA05, 1965TA1E, 1966HA1M, 1966ME1H, 1966UB01, 1967KA05, 1967KE1K, 1967MA11).

For 15 < E_p < 25 MeV, a resonance is found at E_x = 34.4 ± 0.5 MeV, Γ ≈ 4 MeV, ∫ σ(γ₀)dE = 38 eV · b (1963RE09: see, however, (1968BR1M)). The resonance is ascribed to a component of the E1 giant resonance, but the cross section is an order of magnitude less than predicted (1963RE09). (1968BR1M) report no pronounced structure for E_p = 13 to 22 MeV.

See also (1961BL09, 1963FE03, 1963VA1C, 1966AR1D, 1966SU1F, 1967TA1D).

20. ¹¹B(p, n)¹¹C Q_m = -2.763 E_b = 15.957

Excitation functions are reported by (1955BA22: E_p = 2 to 5 MeV, long counter), (1959GI47: E_p = 2.6 to 5.5 MeV, 4π graphite sphere), (1964BA16: E_p = 4 to 14 MeV, 4π graphite sphere), (1961LE11: E_p = 4.9 to 11.4 MeV, ¹¹C activity), (1965SE06: E_p = 3 to 4 MeV, ¹¹C activity), and (1965OV01: E_p = 4 to 11.5 MeV: time-of-flight resolved groups). The excitation functions are characterized by numerous peaks (see Table 12.11 (in PDF or PS)) whose positions appear to correspond with ¹¹B(p, γ)¹²C and with some of the (γ, n) and (γ, p) structure, suggesting that resonances, and not fluctuations, are involved. Angular distributions do not change as rapidly as might be expected from the pronounced structure in the excitation function (1965OV01). The strength of the pronounced peak at E_p = 6.03 MeV (E_x = 21.49 MeV) appears to demand J ≥ 4 (1961LE11). See also (1959GO89, 1960FU1A, 1961GO13).

Polarization measurements have been made for E_p = 7 to 11 MeV (1965WA04). See also (1962AL18, 1963VA1C, 1965VA1E, 1966CA1J, 1966SK03, 1967CA1T) and (1959AJ76).

21. (a) ¹¹B(p, p)¹¹B E_b = 15.957
(b) ¹¹B(p, p')¹¹B*

A pronounced anomaly in the elastic scattering is observed near E_p = 0.67 MeV at all angles; the level is therefore formed by s-waves. The 0.3 to 1.0 MeV results are well accounted for by two resonances: E_p = 0.67 MeV, s-wave, J^π = 2^-, Γ = 0.33 MeV. Γ_p/Γ = 0.5, and E_p = 1.4 MeV, J^π = 1^- (1957DE11). Higher energy structure in the yields of reactions (a) and (b) are displayed in Table 12.11 (in PDF or PS) (1955BA22, 1963AN12, 1965SE06). See also (1960SA28) and Table 12.10 (in PDF or PS).

22. ¹¹B(p, d)¹⁰B Q_m = -9.231 E_b = 15.957

See ¹⁰B.

23. ¹¹B(d, n)¹²C Q_m = 13.732

Reported neutron groups are listed in Table 12.12 (in PDF or PS). Angular distributions of the neutrons to many of the ¹²C states up to E_x = 17.23 MeV have been reported for energies in the range E_d = 0.5 to 10 MeV: see (1957AM48, 1958AM13: 0.5 to 1.15 MeV), (1955WA30: 0.6 MeV), (1955IH1B: 0.69 MeV), (1954GR53: 0.85 MeV), (1957BI78: 0.92 MeV), (1962SA09: 1.0 to 2.0 MeV), (1963KI02: 1.6 to 2.7 MeV), (1961ZD02: 1.1 to 2.8 MeV), (1965SI12: 1.1 to 3.2 MeV), (1965CL02: 1.5 to 4.7 MeV), (1961GA04: 2.7 and 5.4 MeV), (1966HU1H, 1967WI1J: 3.0 to 5.5 MeV), (1965AL17: 2.4 to 9.7 MeV), (1964RO1F, 1966RO1X, 1966WE1B: 6.3 MeV), (1953GI05: 8.1 MeV), (1956MA83: 9 MeV), and (1958ZE01: 10 MeV). See also (1959AJ76) and (1960WA1G, 1961HO1D, 1962LE1A, 1963LA1E, 1964NA02, 1965SI13, 1967DI01).

For E_d less than 6 to 7 MeV, angular distributions of n₀ and n₁ are characterized by both forward and backward peaks, with broad minima near 90°. Detailed shapes are strongly dependent on bombarding energy. The general behavior in the lower-energy range is ascribed to heavy-particle stripping by (1957OW03, 1958AN32, 1961ZD02), but others (1961GA04, 1965AL17, 1966ST1L, 1967WI1J), find reasonable agreement with DWBA, possibly also with compound nucleus effects (1963KI02, 1965CL02). For E_d > 7 MeV, DWBA gives a quite satisfactory account of n₀ and n₁ distributions, except for a single example (n₁ at 8.8 MeV: (1965AL17)). See also (1968YA1G).

Angular correlations of neutrons and 4.4 MeV γ-rays have been studied by (1963HU05: 0.7 and 1 MeV), (1963RI03, 1964RI1D: 1 and 1.2 MeV), (1961ZD02: 1.1 MeV), (1961GA04: 2.65 and 5.35 MeV), (1966RO1X, 1966WE1B: 6.3 MeV). Angular correlations have also been determined for neutrons and 15.1 MeV γ-rays: see (1963KI14: 2.3 and 2.6 MeV), (1960FE01, 1960FE13: 5 and 8 MeV), (1964RO1F: E_d = 6.3 MeV). The formation of the 15.11 MeV state involves l_p = 1 with a 12 : 1 ratio between channel spins 2 and 1. The reduced proton width is approximately equal to the single-particle width (1960FE01, 1960FE13).

In the range E_d = 1.0 to 5.5 MeV, two slow neutron thresholds are observed at 1.627 ± 0.004 MeV (E_x = 15.109 ± 0.005 MeV) and near 4.1 MeV (broad; E_x = 17.2 MeV) (1955MA76). At the lower threshold, 15.1 MeV γ-rays are observed: E_d = 1.633 ± 0.003 MeV, width less than 2 keV (1958KA31) [E_x = 15.110 ± 0.003 MeV].

A study of the angular distributions and energy spectra of α-particles from the decay of ¹²C states shows that the 12.71 and 11.83 MeV states decay sequentially via ⁸Be; the former via ⁸Be*(2.9), the latter 90% via ⁸Be*(2.9) and 10% via ⁸Be(0). There is some evidence that the 10.84 MeV state decays primarily to ⁸Be(0). J^π = 3^- for the 9.64 MeV state is favored on the basis of the angular distribution of the α-particles to ⁸Be(0). There is no evidence for direct 3α decay of ¹²C levels in the range E_x = 9 to 13 MeV, nor does ¹²C*(10.3) appear to participate in this reaction (1965OL01).

See also ¹³C, (1959AJ76) and (1958ED1B, 1962KU02, 1962NA04, 1962RO1L, 1963RO1K, 1965MA1K, 1966ST1L).

24. ¹¹B(³He, d)¹²C Q_m = 10.463
Q₀ = 10.4697 ± 0.0057 (1967OD01).

Observed deuteron groups are displayed in Table 12.13 (in PDF or PS) (1960FO01, 1961HI08). Excitation functions near 10 MeV show no structure; angular distributions exhibit characteristic direct interaction features (1967CR04). See also (1959HO01, 1959WO1B, 1961HO1F) and (1967AD1F).

25. ¹¹B(α, t)¹²C Q_m = -3.858

Differential cross sections have been obtained for the ground-state tritons and for the tritons to ¹²C*(4.4), in the forward direction at E_α = 43 MeV: single-proton transfer seems to be the dominant reaction mode (1967DE1K). The angular distributions appear to be affected by final state spin (1967SI1A).

26. ¹¹B(¹⁴N, ¹³C)¹²C Q_m = 8.407

See (1962NE01).

27. ¹¹B(¹⁶O, ¹⁵N)¹²C Q_m = 3.831

See (1965BO14, 1968KA1L).

28. ¹²B(β^-)¹²C Q_m = 13.370

The decay is mainly to the ground state of ¹²C; branching ratios to other states are listed in Table 12.14 (in PDF or PS). The half-life is 20.41 ± 0.06 msec (Table 12.2 (in PDF or PS)). Since transitions to ¹²C(0⁺) and (2⁺) are allowed, J^π of ¹²B is 1⁺.

Since the decays of ¹²B and ¹²N are mirror transitions, comparison of the ft values has some interest. According to (1964KA08), ft(¹²B) = 11.800 ± 70 sec, ft(¹²N) = 13.060 ± 90 sec; the ratio ¹²N/¹²B is 1.11 ± 0.01: see also (1963FI05, 1963PE10, 1964FI02, 1964NA1C, 1964WU01, 1966BA1A). Possible explanations of the difference are discussed by (1963HU10, 1964EI1C, 1965BL1F, 1966MA2R, 1966OK1B).

Comparison of shape factors for the ground-state β-transitions for ¹²B - ¹²N provides a test of the conserved vector current theory. The correction to the simple Fermi shape should have the form 1 + AE for ¹²B and 1 - AE for ¹²N where A is determined mainly by the (experimental) M1 width of the ¹²C*(15.1) T = 1 level: A(theor.) = 0.52 ± 0.12% MeV^-1 (1958GE1C, 1959GE1D, 1963KI1D, 1964WU01): see also (1959FL41, 1959MO27, 1960WE1C, 1961MO1C, 1967HU10). The experimental values of (1964WU01) are A = 0.55 ± 0.10 and 0.52 ± 0.06 for ¹²B and ¹²N, respectively: see also (1961MA16, 1962LI05, 1962MA22, 1962MC14, 1963GL04, 1963LE05, 1965WU1A).

Transitions to ¹²C*(4.4), J^π = 2⁺, are allowed. According to (1963PE10) the ratio ft(¹²N)/ft(¹²B) = 0.92 ± 0.06. The level energy is 4438.91 ± 0.31 keV (1967CH19).

The level at E_x = 7.6 MeV has special interest for helium burning processes in stars (1963SE17, 1963SE23, 1967FO1B). Observation of the α-spectrum yields Q(¹²C* - ⁸Be - ⁴He) = 278 ± 4 keV (1957CO59). With Q(⁸Be - 2⁴He) = 92.12 ± 0.05 keV (1966BE05), Q(¹²C* - 3⁴He) = 370 ± 4 keV. Using (1965MA54) masses for ⁸Be and ⁴He, ¹²C* = 7647.0 ± 4.1 keV. Although the level decays mainly by α-emission, both the gamma branch to ¹²C*(4.4) and pair emission to ¹²C_g.s. have been observed in various reactions. The relevant parameters are given in Table 12.8 (in PDF or PS) (see (1963AL15, 1963SE23)). The fact that the β-decay is allowed indicates J^π = 0⁺, 1⁺ or 2⁺ for ¹²C*(7.6); observation of the α particles eliminates J^π = 1⁺, and the large Γ_α requires J^π = 0⁺ (1957CO59).

The 10.3 MeV level is observed in both ¹²B and ¹²N decays. The excitation energy given by (1966SC23) is 10.3 ± 0.3 MeV, Γ = 3.0 ± 0.7 MeV. The decay is to ⁸Be_g.s.. With R = 5.2 fm, θ²_α = 1.5 and 7.5 for J^π = 0⁺ and 2⁺, respectively (1958CO66). It is suggested by (1966MO08) that this level is a highly deformed rotational state with J^π = 2⁺, related to ¹²C*(7.66). Some fraction of the observed α-spectrum is presumed to result from a "ghost" of the lower level (1962BA1C, 1963WI05, 1964BL12).

In ¹²N, allowed transitions are observed to ¹²C*(12.7) and (15.1) (AL66J, 1966SC23: see also (1963GL04, 1963WI05)). The 12.7 MeV level decays primarily to ⁸Be*(2.9; J^π = 2⁺); the absence of decay to ⁸Be_g.s. is in agreement with the assignment J^π = 1⁺ (1966SC23). The ft values for both β-transitions (see Table 12.25 (in PDF or PS)) agree well with shell model calculations of (1965CO25). In particular, the agreement strongly suggests a close relation between ¹²C*(12.71; J^π = 1⁺; T = 0) and ¹²C*(15.11; J^π = 1⁺; T = 1). A search for the transition from ¹²B to ¹²C*(12.71) was unsuccessful (1967AL03). See also (1959JA1B, 1960FA02, 1964SH1J, 1966DU1E).

29. ¹²C(γ, γ)¹²C

The lifetime of the 4.4 MeV state has been determined by resonance scattering and absorption as τ_m = 65 ± 12 fsec (1958RA14). See Table 12.8 (in PDF or PS).

Resonance scattering and absorption by the 15.1 MeV level have been studied by (1957HA13, 1959GA09, 1960BU14, 1960HA1H, 1961BU1E, 1963SC21, 1967KU11): partial widths are displayed in Table 12.15 (in PDF or PS). The scattering angular distribution is W(θ) = 1 + cos²θ, indicating dipole radiation (1959GA09); the azimuthal distribution of scattered polarized radiation indicates M1 (1960JA01) and the large Γ(M1) indicates T = 1.

The ground-state γ-width of ¹²C*(16.11) is reported as Γ_γ = 7.5 ± 1.9 eV (1959KE19: see, however, (1961SE10)). For ¹²C*(17.22), the scattering cross section is 1.0 ± 1.0 μb, consistent with Γ_γ given by ¹¹B(p, γ) (1963SC21). See also (1960WE1C).

At higher energies, elastic scattering studies show the giant resonance peak at ≈ 24 MeV (see ¹²C(γ, n)¹¹C), dσ/dΩ(135°) = 4 μb/sr. A considerable tail is visible, extending to > 40 MeV (1959PE32). See also (1958WO53, 1961DE22, 1961WI1G, 1962SE02, 1967LO1B).

30. ¹²C(γ, n)¹¹C Q_m = -18.720

Recent review papers dealing with this reaction are: (1963HA1E, 1965DA1D, 1965SH1G, 1966BA2Y, 1966FU1C, 1966ME1H).

The total absorption, mainly (γ, p) + (γ, n), in the range E_γ = 13 to 30 MeV is dominated by the giant resonance peak at 23.2 MeV, Γ = 3.2 MeV [E_x = 22.6 MeV from ¹¹B(p, γ)¹²C]. This single peak accounts for 64% of the total strength below 27 MeV. The total integrated cross section to 35 MeV is 144 MeV · mb, about 80% of the classical sum rule, 60 NZ/A MeV · mb: see Table 12.16 (in PDF or PS). Other resonant structure is reported at E_γ = (16.5), 17.5, (19.1), 26 and 29 MeV: see Table 12.17 (in PDF or PS) (1960ZI01, 1963BU1G, 1965WY02). See also (1958MO1F, 1958WO53, 1958ZI1B, 1959BU1H, 1959KO55, 1959KU84, 1959PE21, 1960CA09, 1960TA15, 1960WY1A, 1962DE03, 1962MI07, 1963BU18, 1963CO1D, 1965MA1N, 1967BR1P, 1967DR1E).

Shell-model calculations on the structure of the giant resonance ascribe the main effect to four J^π = 1^-; T = 1 levels formed from the particle-hole configurations p^-1_3/2s_1/2, p^-1_3/2d_5/2, p^-1_3/2d_3/2 and s^-1_1/2p_1/2, of which the second contributes most of the E1 strength. The computed energies are 19.6, 23.3, 25.0 and 35.8 MeV [the most probable identifications are E_x = 19.2, 22.6, 25.4 and 34.4 MeV (Table 12.7 (in PDF or PS))] ((1964LE1D), and references therein). Calculations with a deformed potential suggest a somewhat more complicated structure (1962NI1D). See also (1961BA1D, 1962VI01, 1963BO21, 1963MI1B, 1964GI1C, 1964MI1E, 1965DA1D, 1966FU02, 1966LO04, 1966UB01, 1967LE1H, 1967MA1P).

Observations of σ(γ, n) show a giant resonance centered at about 22.5 MeV, σ(peak) ≈ 8 mb, Γ ≈ 3 MeV, with a long tail slopping off to about 40 MeV. The integrated cross section to 40 MeV is about 60 MeV · mb; integrated to 250 MeV, it is about 80 MeV · mb (Table 12.16 (in PDF or PS)). In the giant resonance region, the angular distribution of ground-state neutrons is W(θ) = 1 + 1.5sin²θ, consistent with l_n = 2 ejection (1960EM02, 1964AL33, 1965VE03: see, however, (1967HA1P)). For E_γ = 28 to 145 MeV, comparison with (e, e'n) indicates mainly E1 processes, with ≲ 8% E2 (1958BA60: see also (1961RO1H)).

The giant resonance appears to have a fine structure (Table 12.18 (in PDF or PS)): at least two major components are identified at E_x = 22.0 and 23.5 MeV (1966FU02, 1966LO04: see also (1966CO09, 1967FI1E)). A satellite at E_x = 25.5 MeV is also well established: a large fraction of the decay of this level (6 MeV · mb) involves excited states of ¹¹B and ¹¹C (1966MA1T: see also (1966CO09, 1966FU02)). Up to 28 MeV, about 83% of the neutrons leave ¹¹C in the ground state (1966FU02). Several broad levels are indicated in the range E_x = 27 to 35 MeV (1966CO09, 1966FI1D, 1966FU02, 1967FI1E). A possible level near 52 MeV is reported by (1966FO06). See also (1962BO1H, 1966BI1B, 1966CO09). Considerable fine structure in the range E_x = 19 to 23 MeV is reported by (1959SA06, 1960GE06, 1961TH03, 1966CO09): see also (1959CO62, 1959VA1D, 1960EM02, 1962FU11, 1965MI03).

Polarization of neutrons has been studied by (1964BE1E, 1964HA1F, 1966RA1E, 1967HA1N, 1967HA1P).

31. ¹²C(γ, p)¹¹B Q_m = -15.957

The photoproton cross section exhibits a single broad giant resonance peak centering at E_γ = 22.5 MeV, (Table 12.19 (in PDF or PS)). There appears to be a significant difference from σ( γ, n) both in shape and peak cross section (1963HA1E, 1966FU1C, 1966ME1H): such a difference could result from a comparatively small isospin mixing (1957BA1K). Some fine structure is suggested by the work of (1956CO59, 1962DO1A, 1963MU08, 1963WA18, 1964SH24, 1964TA1G): compare ¹¹B(p, γ)¹²C. The angular distributions near the giant resonance are consistent with W(θ) = 1 + 1.5sin²θ expected on the IPM (1962DO1A). For higher energies, an appreciable cosθ term makes its appearance (1959PE22, 1961VA10, 1963WA18). See also (1965DA1D, 1967FR1E). The azimuthal distribution observed with polarized γ-rays at E_γ = 21.3 - 21.6 MeV is not inconsistent with E1 (1966KE06). Evidence for involvement of excited states of ¹¹B for E_γ > 30 MeV is reported by (1959PE22). See also (1960BA1P, 1963BU1G, 1963FI1B, 1966MA1T, 1966RA1E, 1967LE1H).

At high energies, E_γ ≳ 150 MeV, the cross section for photoproton production remains relatively large (≈ 100 μb) and the angular distributions show forward peaking. The high internal momenta thus implies may be understood on a quasi-deuteron picture, in which the interaction involves neutron-proton pairs in close proximity within the target nucleus (1951LE1B). This picture is strongly supported by the observation that most, if not all, high energy photoprotons are accompanied by neutrons with the proper kinematical relation (1954MY1A, 1958BA1C, 1958WH35); see, however, (1965RE1B).

Experimentally derived momentum distributions are reported by (1961CE1B, 1963KI03, 1963KI1C). See also (1958MA1A, 1959CH25, 1961MA36, 1961SH1C, 1962CH26, 1962PA08, 1964JI1A). Polarization of the photoprotons has been studied by (1962LI13).

32. ¹²C(γ, d)¹⁰B Q_m = -25.188

For E_brems = 90 MeV, the ratio of yields of deuterons to protons is ≈ 2%, for particle energies 15 to 30 MeV. For higher particle energies, the ratio decreases. Angular distributions are similar for (γ, d) and (γ, p), with strong forward peaking. These observations are consistent either with a quasi-deuteron mechanism or with a two-stage pickup process (1962CH26: see (1962MA1F, 1964SH1B)). According to (1964SH1B) the high apparent threshold for ( γ, d) reflects the presence of continuum states of ¹⁰B with a high parentage in ¹²C. See also (1959CH25, 1960SH1D, 1963BA1K, 1964KI1D, 1965KI04, 1967SM1A).

33. ¹²C(γ, t)⁹B Q_m = -27.369

See (1968BU1D).

34. ¹²C(γ, 3α) Q_m = -7.274

The cross section exhibits broad peaks at about 18 MeV and ≈ 29 MeV; a pronounced minimum occurs at 20.5 MeV: to what extent the peaks have fine structure is not clear (1953GO13, 1955CA19, 1955GO59, 1955JO1C, 1964TO1A).

For E_γ < 22 MeV, transitions are mainly to ⁸Be_g.s. and ⁸Be*(2.9) with the g.s. transition dominating for E_γ ≲ 14 MeV. For E_γ > 26.4 MeV, ⁸Be (T = 1) levels near 17 MeV are strongly excited (1955GO59). Integrated cross sections are 0.82 ± 0.03 MeV · mb (1964TO1A: to 20.5 MeV), 1.21 ± 0.16 MeV · mb (1953GO13: to 20.5 MeV), 2.8 ± 0.4 MeV · mb (1953GO13: 20.5 to 42 MeV) and < 0.2 MeV · mb (1953GO13: 42 to 60 MeV). Alpha energy distributions show surprisingly strong E1 contributions below E_γ ≈ 17 MeV (1955GO59, 1964TO1A). See also (1958MA1A, 1960GA16, 1961SE13, 1964WA1J, 1965RO1J), and (1959YO1B, 1964LE1C, 1965DZ1A, 1965DZ1B).

35. (a) ¹²C(γ, pα)⁷Li Q_m = -24.621
(b) ¹²C(γ, nα)⁷Be Q_m = -26.265

Reported integrated cross sections for reaction (a) are for 25 to 40 MeV: 1.61 MeV · mb (1962MO16), 1.35 MeV · mb (1956LI05), 3.85 MeV · mb (1958MA1A); for 25 to 120 MeV: 1.9 ± 0.4 MeV · mb (1962MO16). For production of ⁷Be (reaction (b)), the integrated cross section to 57 MeV is 6.0 ± 0.4 MeV · mb (1966AR01).

36. ¹²C(e, e)¹²C

Elastic scattering has been studied up to 800 MeV: momentum transfers q² ≤ 11.5 fm^-2 (1959ME24, 1964CR11, 1966CR07). The form factor is well accounted for by a harmonic-well model with R(r.m.s.) = 2.40 ± 0.02 fm. Only one diffraction minimum is observed (1966CR07). R = 2.42 ± 0.04 fm (1967EN1C), R = 2.58 fm (1967EL1B), R = 2.35 ± 0.1 fm (1966AF1A: see also (1967AF02, 1967AF04, 1968AF1A)). See also (1960IN1A, 1963GO04, 1965MU1B, 1965RA1F, 1967BE1P, 1967BO1X, 1967EL1B, 1967FR1D, 1968BR1N).

Sharp inelastic peaks are reported corresponding to ¹²C*(4.4, 7.7, 9.6, 15.1 and 16.1 MeV) (1956FR27, 1956HE83, 1959BA36, 1959EH1A, 1960BA47, 1961BO32, 1961DU09, 1962ED02, 1963BO36, 1963GO1P, 1964BR1N, 1964CR11, 1964GO14, 1965GU04, 1966CR07, 1967AR1A, 1967CR01, 1967PE07). Observed widths are reported in Table 12.20 (in PDF or PS). Additional structure in the range E_x = 16.6 to 25.5 MeV is reported by (1963BO36, 1966PR1C). The variation of the form factor F(q²) with momentum transfer yields unambiguous assignments of J^π = 2⁺, 0⁺ and 3^- for the first three levels (1960BA38, 1964CR11, 1967HA1U). There is some evidence of a diffraction structure in F(¹²C*(4,4)) at high momentum transfer (1966CR07). Transverse and longitudinal scattering form factors from ¹²C*(4,4) have been measured by (1967BE43).

The 15.1 MeV transition is a strong M1: J^π = 1⁺; T = 1: the indicated Γ_γ is somewhat lower than the mean from ¹²C(γ, γ) (1964GO15, 1964GU05, 1965FO1F). The theoretical value is sensitive to the spin-orbit coupling parameter, but a pure p⁴_3/2 ground state seems to be excluded (1964BI1H, 1964KU1G). The 16.1 MeV level corresponds to that observed in ¹¹B(p, γ)¹²C. Γ_γ₀ = 0.184 ± 0.045 eV is obtained from the electron data, and T = 1 is confirmed (1961DU09, 1964BI1H, 1965BI1B, 1966PR1C). See also (1960IN1A, 1962KU1C, 1963BO36, 1964GI1A, 1965IN1A, 1965SE1D, 1967SH1L).

Inelastic excitation of the giant resonance has been studied by (1959BA36, 1960BA47, 1961BO32, 1963BO36, 1963GO1P, 1963LE1H, 1964GO14, 1966PR1C). There appears to be evidence for structure at 18.1 ± 0.05, 19.5 ± 0.05 (Γ = 0.5 ± 0.1), ≈ 24 and ≈ 34 MeV (1964GO14: see also (1967CR02)). The variation of F(q²) with q² in the range 0 - 0.6 fm ^-2 shows good agreement with the calculations of (1964LE1D) which assumes four 1^- particle-hole states at E_x = 19.6, 23.3, 25.0 and 35.8 MeV (see also (1967CR02)). See also (1960FA1E, 1965LE1D, 1966FR1H, 1966UB01, 1967BI1K). Reported integrated cross sections are 75 MeV · mb (1960BA47), 50 MeV · mb (1963GO1P). See also ¹²C(γ, n)¹¹C. The behavior of the 19.2 MeV level suggests ascription to the expected giant magnetic quadrupole state J^π = 2^-; this state is not likely to have been seen in ¹¹B(p, γ)¹²C (1965DE1C, 1965DE1K, 1966BE1Q, 1967BI1K, 1967CR02, 1967DR1C). A positive parity state with a large longitudinal matrix element may also be present (1967BI1K).

See (1962BA1D, 1964BA1R, 1966DE1K, 1966GO1C, 1967WA1E, 1967WA1F) for general discussions.

37. (a) ¹²C(e, e'p)¹¹B Q_m = -15.957
(b) ¹²C(e, e'n)¹¹C Q_m = -18.720

Electron spectra in the region of large energy loss show a broad peak which is ascribed to quasi-elastic processes involving ejection of single nucleons from bound shells: see (1961BO32, 1963CZ1A, 1966DE1K). A study of e' - p coincidences for incident energies around 550 - 600 MeV reveals peaks corresponding to ejection of 1p and 1s protons: the results are consistent with observations in (p, 2p) (1961JA1L, 1964AM1C, 1967AM1E). Angular distributions for the two groups are analyzed by (1967AM03) in terms of proton momenta.

38. (a) ¹²C(n, n)¹²C
(b) ¹²C(n, n')¹²C*
(c) ¹²C(n, n')⁴He⁴He⁴He Q_m = -7.274

Elastic and inelastic scattering have been studied at many energies up to 350 MeV. The data are summarized by (1963GO1M, 1964ST25); some later references are listed in Table 12.21 (in PDF or PS). At E_n = 14 MeV, the elastic angular distribution shows a forward-peaked diffraction structure indicating direct interaction. Optical model fits in the forward hemisphere are satisfactory but fail at back angles (1963LU10, 1964CL05). A strong-coupling calculation has been made by (1965BL09). polarization studies at E_n = 24 MeV are in fair agreement with optical model predictions and yield a sign for the spin-orbit coupling in agreement with shell model predictions (1962WO08: see also (1960SA1E, 1965BR1E)). See also (1959GL57, 1959KE1A, 1959WI1C, 1960HO14, 1960RO24, 1964CR1B).

At 14 MeV the cross sections for n₀, n₁ (4.4) and n₂ (9.6) are about 800, 220 and 100 mb, respectively: see (1963BO15, 1964ST25, 1966GR1L, 1967GR1P). Angular distributions at E_n = 14 MeV of neutrons corresponding to ¹²C*(4.4) show direct interaction, but DWBA optical model fits are unsatisfactory (1964CL05: see also (1959GL57, 1960PE02, 1960RO24)). (1967GR1P) find that coupled channel calculations, with ¹²C*(0, 4.44, 9.64, 10.84) taken as collective states yield fair agreement with the experimental angular distributions at E_n = 14 MeV. See also (1962BA15, 1962BA25, 1962CO1E, 1963HO08, 1964JO1E). The angular correlation (n', γ_4.4) has forward neutron angles the distributions are similar to (p, p'γ) while a strong difference is apparent at θ_n = 135° (1963BE31, 1966BE1R). See also (1961AS1B, 1963MO04, 1964MO1D, 1965LA1D). See also (1958AN32, 1958NA09, 1959GA1D, 1959HA06, 1959SI79, 1960DE10, 1960HE10, 1960PE1A, 1961BR08, 1961JA19, 1961ST22, BL62C, 1962BO06, 1962BR11, 1962ST18, 1962TE05, 1963ED1B, 1963GA1G, 1963KO1C, 1963MC1B, 1963OP1A, 1963SE1P, 1964AD1B, 1964EN1B, 1964OL1B, 1964PE20, 1966BR1D, 1966CI1A, 1966FE1C, 1966JO1B, 1966KA1E, 1966KO1D, 1966LI1F, 1966MO1C, 1967BR23, 1967CH1R, 1967LE1G) and ¹³C.

At E_n = 14.2 MeV, reaction (c) proceeds about 50% through ¹²C states which then decay via ⁸Be_g.s. and ⁸Be*(2.9). Most of the remainder of the observed events take place through ¹²C(n, α)⁹Be* → n + ⁸Be* and ¹²C(n, α)⁹Be* (α) ⁵He* (n) α. The reaction ¹²C(n, ⁵He*)⁸Be* cannot be excluded. Four-body break-up is not necessary to explain the results. The α-decay of the 10.8 and 11.8 MeV states, together with stripping results, suggest J^π = 1^- and 2^- for these states (1964BR25: see also (1966MO05)). See also (1959TS1A, 1960VA10, 1962BA15, 1962BA25, 1964SA1E, 1965GR1V, 1965GR1W, 1966CI1A, 1966FE1C, 1966GR1M).

39. (a) ¹²C(p, p)¹²C
(b) ¹²C(p, pn)¹¹C Q_m = -18.720
(c) ¹²C(p, 2p)¹¹B Q_m = -15.957
(d) ¹²C(p, pd)¹⁰B Q_m = -25.188
(e) ¹²C(p, pα)⁸Be Q_m = -7.369

Up to E_p ≈ 12 MeV, the elastic scattering exhibits resonance structure: see ¹³N. References to elastic and inelastic studies at higher energies are listed in Table 12.22 (in PDF or PS). Excitation functions for both (p, p) and (p, p₁(4.43)) exhibit pronounced resonance-like structure for E_p = 14 to 20 MeV (1957PE14, 1961NA02, 1964DA03). An optical model analysis gives a good account of the data, but the parameters vary strongly with energy (1962NO03: see also (1962RO14)). Between 18 and 30 MeV the elastic scattering and polarization angular distributions show strong energy dependence, while those for inelastic groups are much smoother (1963DI04, 1963DI16, 1966CR04). An optical model analysis with resonances is discussed by (1964TA1E); see also (1965BA1M). At 40 MeV an 11-parameter optical model fit is satisfactory for elastic differential cross sections, but unsatisfactory for polarization data (1966BL19, 1967FR20: see also (1965BA54, 1965FR17)). The same problem arises with the data at 46 MeV (1967SA13) and 49 MeV (1966CR14). For analysis of the 140 MeV small angle results, see (1966JA08). See also (1958BE1B, 1959WI1C, 1962RO1F, 1964CR1B, 1967BE1Q, 1967TA1B). At 1 MeV, the differential elastic scattering cross section exhibits diffraction-like structure associated with the multiple scattering of protons by nucleons inside the nucleus (1967PA25).

At E_p = 40 MeV, angular distributions of inelastic protons corresponding to ¹²C*(4.4, 7.7, 9.6) confirm the assigned parities even, even, odd, respectively. Comparison of deformation parameters for ¹²C*(4.4) determined by (p, p'), (α, α') and (e, e') show considerable differences (1964ST15): see, however, (1966BA2K, 1967SA13). Angular distribution measurements at E_p = 46 MeV (1967PE05) have been analyzed by (1967SA13): a large quadrupole deformation was found (β₂ ≈ 0.6); the inelastic scattering agrees best with deformation of both the real and imaginary parts of the optical potential; the angular distribution for ¹²C*(7.6) is best described by double quadrupole excitation via ¹²C*(4.4). ¹²C*(14) is interpreted as the 4⁺ rotational state. The similarities of distributions corresponding to ¹²C*(10.8, 11.8) suggest that they have the same spin (1967SA13). Asymmetries observed with 40 MeV polarized protons on ¹²C*(4.4) disagree with DWBA predictions (1966FR1G: see also (1967SA13)). See also (1960BA38, 1963DI16, 1964DA03, 1965FR17, 1966BL19, 1967FA06, 1967LE13, 1967LE1G, 1967PA1L, 1967SA1L, 1968GA1H, 1968TA1P).

A number of inelastic groups have been studied at E_p = 155 to 185 MeV: see Table 12.23 (in PDF or PS). When treated in the impulse approximation, the cross sections and angular distributions are closely related to the electric transition moments. Comparison of (p, p') and (e, e') form factors yield the transition multipolarities indicated in Table 12.23 (in PDF or PS) (1964JA03: see also (1960NI02, 1961BR08, 1961PI04, 1962BR11, 1962RO1F, 1962SA1G, 1963HO1D, 1963NI02, 1964HA1L, 1965HA17, 1965HA28, 1966HA51, 1967HA1U, 1967JO1F). The broad levels reported in the range E_x = 20 to 24 MeV are associated with the giant E1 resonance (1961SA1E, 1962SA1G, 1963DE35, 1965HA17).

The energy of the first excited state is 4440.0 ± 0.5 keV, from the γ-ray. The character of the Doppler broadening indicates rather little spin-flip contribution to the inelastic scattering (1967KO14: E_p = 23 MeV). Proton γ-angular correlations provide a sensitive measure of the spin-flip: for E_p = 10 to 15 MeV a considerable contribution is observed (1964SC07, 1966SC1L: see also (1961AD04, 1961CL1D, 1961GI1C, 1961GO13, 1962NO04, 1964BA14, 1964RO23, 1967GI1D, 1967KO1N) and Table 12.21 (in PDF or PS)).

The following is a list of other recent theoretical and review papers dealing with this reaction: (1959GL57, 1959HO95, 1959MC63, 1959PU1A, 1960BE31, 1960LU1B, 1960MA43, 1960MI1C, 1960SA1C, 1960SA1E, 1960SA1G, 1961DO1C, 1961GI1D, 1961MC1C, 1961SA1B, 1962KA1E, 1962MA1P, 1962NI1C, 1963BU1E, 1963LO1A, 1963VI1A, 1964DA07, 1964HO1C, 1964SA1L, 1965CL1E, 1966BO1P, 1966GI1A, 1966LI1F, 1966SA1D, 1967CH1R, 1967VA1K) and (1959AJ76).

Reaction (b) is widely used to monitor high-energy proton beams: see (1963CU05, 1963CU1B). For studies of recoil spectra, see (1962SI09, 1965BE1U). Possible emission of singlet deuterons is discussed by (1966NO1A). See also (1967HO1M).

In the summed proton spectrum of reaction (c), peaks are observed corresponding to the ejection of p- and s-shell protons: see ¹¹B. Absolute cross sections are reported by (1965GI1F). See also (1962AU1A, 1962ST1F, 1964LI1D, 1964LI1E, 1965MC1F, 1965RI1A, 1966BE1B, 1966KO1F, 1966JA1A, 1967CO1V, 1967EL1C, 1967GO01, 1967JA1C, 1967RI08, 1968JA1G, 1968YU1B). At E_p = 57 MeV the reaction involves an excited state at 20.3 MeV (1967EP1B, 1968RO1L).

For reaction (d) see (1963SH1A, 1965BA11, 1967SU1C, FR68A). See also (1962AU1A, 1964BA1P).

Reaction (e) has been studied up to E_p = 660 MeV. Various states in ¹²C appear to be involved. At E_p = 57 MeV, the sequential process dominates; α-decay to ⁸Be_g.s. is observed via ¹²C*(21.1, 22.2, 26); comparison with other reactions suggests (J^π; T) = (1⁺, 3⁺; 0), (1^-; 0 + 1); (π = natural; significant T = 0 component) (1967EP1B). See also (1966RO1D, 1968RO1L). See also (1959VA15, 1960VA10, 1961VA17, 1962VA1A, 1962ZH1B, 1963JA07, 1963VA04, 1963ZH1A, 1964BA29, 1964KE1F, 1964SY02, 1964YU1A, 1965IS05, 1965KU14, 1965SA1K, 1965YU1C, 1965ZH1A, 1966JA1B, 1966ZE1A, 1967GA01) and (1959AJ76).

Total proton reaction cross sections are reported by (1959BU97, 1959GO90, 1964GI05, 1964GR1M, 1967CA1K).

40. (a) ¹²C(d, d)¹²C
(b) ¹²C(d, pn)¹²C Q_m = -2.224

The angular distribution of elastically scattered deuterons has been studied at a number of energies from E_d = 2.8 to 650 MeV: see (1954FR24, 1960BU25, 1960CA24, 1961IG02, 1961IS02, 1961LO01, 1962SL02, 1963BU24, 1963CA1E, 1963FR1F, 1963VA23, 1965DI1C, 1965DU01, 1966CO24, 1966DO1B, 1966DU08, 1966GA09, 1966GE03, 1966NG01, 1967AU05, 1967DU1E, 1967FI07, 1967NE09, 1967PL1B, 1967WA1M). Inelastic groups corresponding to levels at 4.4 and 9.6MeV are reported by (1961JA02, 1962SL02, 1966NG01: see also (1951KE02, 1954FR24, 1956GR37, 1956HA90)). The angular distributions of inelastically scattered deuterons to these two states and to ¹²C*(7.7) have been measured at E_d = 25.9 MeV (1963VA23). A systematic optical model analysis yields a set of smoothly varying parameters which give a good account of the elastic angular distributions from E_d = 3 to 34 MeV. For the inelastic scattering, Q = -4.4, deformation of the potential corresponding to β = 0.4 - 0.6 was required (1966SA1C). See also (1961CI08, GO61I, 1963CA1J, 1963SA1G, 1968HI1H), (1958MA52, 1960EL09, 1960FA05, 1960LU1B, 1961RO1G, 1962SA1J, 1963ST1A, 1963ZA1B, 1964HE1H, 1964HO1C, 1964RU1A, 1964SA1K, 1965CA1F, 1965TJ1A, 1966BA2W, 1966JA1J, 1966MA2Q, 1967RE1E, 1967RU1A; theor.) and (1959AJ76).

For reaction (b), see (1963PH1A, 1965LA08, 1965LA1F, 1967MA1N, 1967NO1A) and ¹³N.

41. ¹²C(d, ⁶Li)⁸Be Q_m = -5.897

Differential cross sections measured for E_d = 14.7 MeV are analyzed by DWBA to yield S_α, a measure of the composition ⁸Be + α in the wave function of ¹²C_g.s.. Subject to an uncertain normalization, S_α is found to be close to unity (1964DA1B, 1966DA1C, 1966DE09).

42. ¹²C(t, t)¹²C

Angular distributions of elastically scattered tritons have been determined at E_t = 1.0 to 1.75 MeV (1962GU01: see also (1968HE1N)), at 6.4, 6.8 and 7.2 MeV (1964PU01) and at 12 MeV (1965GL04: optical model analysis; see also (1966GL1B)).

43. (a) ¹²C(³He, ³He)¹²C
(b) ¹²C(³He, pd)¹²C Q_m = -5.494

Angular distributions of elastically scattered ³He particles have been determined for E(³He) = 2 to 6 MeV (1966SC12), 5.5 MeV (1961PA04), 8.5 and 10 MeV (1966SC22), 12 MeV (1965YO1B), 12.0 to 18.6 MeV (1967FO1F), 20.1 MeV (1967MA1G: also ¹²C*(4.4)), 24.5, 25.3 and 26.8 MeV (1964SE05), 25.7 MeV (1966DA1H: also ¹²C*(4.4, 7.7)), 26.1 to 32.6 MeV (1963PA15: also ¹²C*(4.4)) and 29 - 30 MeV (1961AG1A, 1961CA18, 1962AG01, 1962CA29, 1962GA17, 1965BU1H, 1967BA2P, 1967BR1N). See also (1961FO02, 1962WE1C, 1967AR17, 1967AS1B) and (1961HO1J, 1964GO1J, 1965FR1E, 1967GR1N, 1967PA1U; theor.). For reaction (b) see (1965DO1H).

44. (a) ¹²C(α, α)¹²C
(b) ¹²C(α, αn)¹¹C Q_m = -18.720
(c) ¹²C(α, 4α) Q_m = -7.274

Angular distributions of elastic and inelastic α-particles and of 4.43 MeV γ-rays have been measured at a number of energies: see Table 12.24 (in PDF or PS). DWBA fits to differential cross sections observed at 40.5 MeV for Q = -4.4 yield B(E2)(↓) = 13 e² · fm⁴; for Q = -9.6, B(E3)(↓) = 50 - 70 e² · fm⁶ (1966HA19). Except for the broad 10.1 MeV state all known levels of ¹²C with E_x < 14 MeV have been observed by (1966HA19). Angular distributions of α-particles and 4.4 MeV γ-rays have been studied at E_α = 22.5 (1964EI01) and at 43 MeV (1959SH62, 1962MC11). The studies of (1962MC11, 1964EI01) yield information on the polarization of the ¹²C*(4.4) as produced in inelastic scattering. The derived polarizations show strong dependence on scattering angle and are not explained by simple PWBA or adiabatic reaction mechanisms: DWBA gives qualitative agreement. Similar studies involving ¹²C*(9.6) confirm that J^π = 3^- (1963LA07). See also (1959CA14, 1962BR14, 1964BU1F, 1964LA07, 1967VE1C) and (1959BL31, 1959GL57, 1960RO1E, 1961EI1A, 1962RE1C, 1963DA1B, 1963HO1J, 1964DA1D, 1964GR1L, 1965JA1D, 1966JO1A, 1967BO1W, 1967JA1G, 1967LA1K; theor.) and (1959AJ76). The 9.6 MeV state decays predominantly through ⁸Be_g.s. (1966BO28).

The angular distribution of alphas corresponding to ¹²C*(12.7; J^π = 1⁺) at E_α = 28.5 MeV is not accounted for in DWBA. A spin-orbit interaction leading to spin flip appears to be involved (1967NA06).

For reaction (b) see (1953LI28). Angular correlations in ¹²C(α, 2α) (reaction (c)) observed at E_α = 915 MeV give evidence for strong α-clustering in ¹²C (1961GO1T). See also (1961VA38, 1962BR14, 1962VA25, 1965YA02).

45. (a) ¹²C(⁶Li, ⁶Li)¹²C
(b) ¹²C(⁷Li, ⁷Li)¹²C

See (1964OL1A); see also (1963BE1R, 1966DE09, 1967SI1C).

46. (a) ¹²C(¹⁰B, ¹⁰B)¹²C
(b) ¹²C(¹¹B, ¹¹B)¹²C

See (1964OL1A). See also (1963SH1E) for reaction (a) and (1963SA1E) for reaction (b).

47. ¹²C(¹²C, ¹²C)¹²C

At E(¹²C) = 126 MeV, strong inelastic peaks corresponding to ¹²C*(0, 4.4, 14.0 ± 0.5) have been observed. Groups with Q = -9 and -19 MeV are also seen. Their interpretation is less clear. Angular distributions suggest that the 14 MeV state has J^π = 4⁺; the large intensity indicates close association with ¹²C_g.s. (1962WA24, 1963GA05, 1966BA2K); deformation parameters are listed by (1966BA2K); see also (1962GA02, 1962WI09). The elastic scattering has also been studied for E_c.m. = 3 to 13.4 MeV (1961BR15) and at E_c.m. = 56.7 MeV (1962SM02). See also (1965GR1F), (1959AL1H, 1962BE43, 1962SE1G, 1963WI1G) and (1962BU1B, 1963BA1Y).

48. ¹²C(¹⁴N, ¹⁴N)¹²C

Differential cross sections have been determined for the ¹²C_g.s. transition at E(¹⁴N) = 21.5 to 27.3 MeV (1960HA16) and at E_c.m.(¹⁴N) = 62.5 MeV (1962SM02); those to the 4.4 MeV state have been measured at E(¹⁴N) = 27.3 MeV (1961HA04). See also (1961KU1D, 1961NE04, 1962WI09) and (1963KU1L).

49. ¹²C(¹⁶O, ¹⁶O)¹²C

Differential cross sections have been determined for the ¹²C_g.s. transition at E_c.m.(¹⁶O) = 8 to 13.7 MeV (1963KU12) and at E(¹⁶O) = 35 (1967GO1A, 1968VO1D), 42 (1964NE01), 67 (1959MC1D) and 168 MeV (1964HI09): those to the 4.4 MeV state have been measured at E(¹⁶O) = 42 and 168 MeV (1964HI09, 1964NE01).

A DWBA analysis of the 168 MeV data is given by (1966BA2K). See also (1963KU1L, 1967AB1D).

50. (a) ¹²C(¹⁷O, ¹⁷O)¹²C
(b) ¹²C(¹⁸O, ¹⁸O)¹²C

The elastic scattering angular distributions in both (a) and (b) have been measured at E = 35 MeV (1967GO1A).

51. ¹²N(β⁺)¹²C Q_m = 17.342

The decay is mainly to the ground state via an allowed transition. Branching fractions to other states of ¹²C are listed in Table 12.25 (in PDF or PS). The half-life is 10.97 ± 0.04 msec; see Table 12.28 (in PDF or PS). Since transitions to ¹²C_g.s. and ¹²C*(4.4) are allowed, J^π(¹²N) = 1⁺. See discussion of ¹²B(β^-) and (1965WU1A). See also (1962PO02, 1966DU1E, 1967HU10).

52. ¹³C(γ, n)¹²C Q_m = -4.947

See ¹³C.

53. ¹³C(p, d)¹²C Q_m = -2.722

Angular distributions of deuterons to ¹²C*(0, 4.4) have been measured by (1966GL01: 8 and 12 MeV) and by (1961BE12: 17 MeV). For the ground state, θ² = 0.036 at E_p = 8 MeV and 0.058 at 12 MeV; for the 4.4 MeV state θ² = 0.051 at 12 MeV (1966GL01: PWBA). See also (1960NE1C, 1964TE1G). At E_p = 54.9 MeV, strong deuteron groups are observed to ¹²C*(0, 4.4, 12.7, 15.1, 16.1) and partial angular distributions of these groups have been observed. Spectroscopic factors (from DWBA) indicate that the summed transition strengths to the four excited states are approximately equal to the P_3/2 neutron pickup strength in ¹²C(p, d) (1968TA1V).

54. ¹³C(d, t)¹²C Q_m = 1.311
Q₀ = 1.311 ± 0.006 (1961TE02, 1964MA57);
Q₀ = 1.3109 ± 0.0007 (1967OD01).

Angular distributions of tritons have been obtained by (1954HO48: 2.2 and 3.3 MeV; t₀), (1966GL01: 8 and 12 MeV; t₀ and t₁), (1960MA10: 14.8 MeV; t₀, t₁, t₂). The relative θ² for the ground and first two excited states are 1 : 0.76 : 0.039 (1960MA10, 1966GL01: PWBA). Assuming θ² = 0.031 for ¹²C_g.s., θ² = 0.024 for ¹²C*(4.4) and 0.0012 for ¹²C*(7.7) (1960MA32). See also (1959KU1C, 1963OG1A, 1965DE26, 1967DE1J).

55. ¹³C(³He, α)¹²C Q_m = 15.631

Angular distributions have been determined at many energies: see (1962CH02: 1.6 to 3.3 MeV; α₀, α₁, α₂), (1968MI1H: 1.66 to 3.12 MeV; α₀, α₁, α₂), (1957HO63: 2 MeV; α₀, α₁), (1960BA25: 1.8 MeV; α₀), (1957HO62: 4.5 MeV; α₀, α₁), (1964DE1E, 1965DE26: 8.8, 9.4, 10.3 MeV; α₀, α₁; DWBA), (1966KE08: 12, 15, 18 MeV; α₀, α₁, α₂, α₃, α₅, α₆, α₇, α₈; DWBA), (1967BA2G: 40 - 45 MeV). (1966KE08) find l = 1 or 0 for all the groups except α₃ (to ¹²C*(9.6)) for which l = 2. Angular correlations of α-particles and 4.4 MeV γ-rays have been studied at E(³He) = 4.5 MeV (1962HO13). See also (1968NO1E). The 15.1 MeV γ-ray has been observed: see (1957BR18, 1959AL96, 1959BR79). See also (1959OW1A, 1961HO1F, 1964EL1B, 1965NE1B, 1967BH1B).

56. ¹⁴C(p, t)¹²C Q_m = -4.641

At E_p = 18.5 MeV, the angular distribution of the tritons to the ground state has been determined: l = 0 (1961LE1A, 1963LE03).

57. ¹⁴N(γ, d)¹²C Q_m = -10.272

Not reported.

58. ¹⁴N(n, t)¹²C Q_m = -4.015

At E_n = 14-15 MeV, the angular distribution of the tritons to the ground state has been fitted with L = 2 (1967AN08, 1967FE06, 1967LI06, 1967RE01). See also (1959GA14, 1967BA1E, 1967MO21).

59. ¹⁴N(p, pd)¹²C Q_m = -10.272

See (1964BA1C, 1967FU1A).

60. ¹⁴N(p, ³He)¹²C Q_m = -4.779

At E_p = 40 MeV, angular distributions of the ³He to ¹²C*(0, 4.4) have been determined. They show strong forward peaking (1966BR1X, 1966HO1F). See also (1961CL09, 1962MA1L, 1967HO1N).

61. ¹⁴N(d, α)¹²C Q_m = 13.575
Q₀ = 13.579 ± 0.006 (1964MA57: see also (1962TE02)).

Alpha groups have been observed corresponding to all ¹²C states up to ¹²C*(16.11), with the exception of ¹²C*(10.3) and ¹²C*(14.7) (see (1965BR08)). See Table 12.26 (in PDF or PS) for a listing of energy parameters measurements. Angular distributions have been obtained at many energies: see (1966EU01: 0.5 to 2.2 MeV; α₀), (1961SJ1B: 0.6 to 0.8 MeV; α₀), (1965WI11; 0.8 to 1.9 MeV; α₀, α₁), (1965ST02: 0.9 to 1.2 MeV; α₀, α₁), (1960KA1H: 1.4 to 2.9 MeV; α₀), (1961IS03: 1.5 to 3 MeV; α₀), (1965SC12: 4 MeV; α₀, α₁, α₂, α₃, α₅, α₆, α₇; 7.2 MeV; α₇, α₈, α₉, α₁₁), (1965BR08: 5.9 and 7.2 MeV; α₇, α₁₁, α₁₂), (1964CH1C: 4, 6, 8 and 10 MeV; α₀, α₁, α₂), (1962WI05: 10 MeV; α₀, α₁), (1960HU10: 10.3 to 11.4 MeV: α₀, α₁), (1966DR04: 11.3 and 12.6 MeV; α₀, α₁), (1961YA08: 14.7 MeV; α₀, α₁), (1959BO40, 1959HE1C: 20.0 MeV; α₀), (1959FI30: 20.9 MeV; α₀, α₁, α₃), (1965PE17: 24 MeV; α₀, α₁, α₂, α₃), (1966VI1A: 28.5 MeV; α₁). Integrated cross sections for eight alpha groups have been obtained at E_d = 11.8 MeV (1966JA05). At E_d = 24 MeV, α₁ is strongly favored over α₀, and α₃ is favored over α₄. For α₀, α₁ L = 2 is preferred (1965PE17). Angular distributions at E_d = 4 MeV are nearly symmetric about 90°, suggesting a compound nucleus process involving many overlapping levels (1965SC12).

In a test of isospin conservation, (1965BR08) find, at E_d = 7.2 MeV, the cross section for excitation of ¹²C*(15.11, J^π = 1⁺; T = 1) = 31% of that for ¹²C*(12.71, J^π = 1⁺; T = 0); σ(16.11)/σ(12.71) = 4%. Violation of this order can be understood as being due to coulomb mixing in the compound nucleus.

Comparison of angular distributions of ¹⁴N(d, α)¹²C at E_d = 20 MeV and ¹²C(α, d)¹⁴N at E_d = 41.7 MeV suggest an upper limit of 3% for the time reversal non-conserving fraction of the Hamiltonian (1959BO40, 1959HE1C, 1965PE17). See also (1962AL09, 1966ME1E).

At E_d = 1.8 MeV, the alpha particles to the 7.65 MeV state were observed in coincidence with recoiling ¹²C_g.s. nuclei. If Γ_rad ≡ (Γ_γ + Γ_π), the ratio Γ_rad/Γ = (2.8 ± 0.3) × 10^-4: see ¹²B(β^-)¹²C (1963SE23). See also (1967UI01).

62. ¹⁴N(³He, pα)¹²C Q_m = 8.081

See (1962BL1E) and ¹⁶O.

63. ¹⁴N(α, ⁶Li)¹²C Q_m = -8.800

At E_α = 42 MeV, angular distributions of ⁶Li ions corresponding to the ground and first excited states of ¹²C have been measured (1964ZA1A). See also (1964BR1L).

64. ¹⁴N(¹⁰B, 3α)¹²C Q_m = 7.642

See (1965SH1A).

65. ¹⁵N(p, α)¹²C Q_m = 4.965
Q₀ = 4.954 ± 0.008 (1961LO10).

Searches for double dipole de-excitation of the 4.4 MeV state have been unsuccessful Γ_E1E1/Γ_E2 ≤ 0.5 × 10^-4 (1964AL18), ≤ 1.7 × 10^-4 (1960MC03). A theoretical estimate of 10^-8 is cited by (1960MC03).

Angular distributions of α-particles leading to the ground and 4.4 MeV states have been determined for E_p up to 18.6 MeV: (see (1963MI1H, 1963RO01, 1964EC03, 1965WA1N, 1967NO02)). At the higher energies the ground-state alpha particles show marked backward peaking, in agreement with the inverse reaction ¹²C(α, p)¹⁵N (1964EC03). See also (1963NA1C, 1964HO1D, 1966EV1B).

66. ¹⁵N(α, ⁷Li)¹²C Q_m = -12.382

Angular distributions of the ⁷Li ions to the ground and 4.4 MeV states have been determined at E_α = 42 MeV (1966MI1M).

67. (a) ¹⁶O(γ, α)¹²C Q_m = -7.161
(b) ¹⁶O(γ, 4α) Q_m = -14.436

There is evidence for the involvement of many ¹²C states: see (1965RO05, 1967CA1C).

68. (a) ¹⁶O(n, nα)¹²C Q_m = -7.161
(b) ¹⁶O(p, pα)¹²C Q_m = -7.161
(c) ¹⁶O(α, 2α)¹²C Q_m = -7.161

For reaction (a), see (1963MO04, 1964MO1D). In reaction (b), 4.4 MeV γ-rays are observed at E_p = 146 (1962FO03) and 150 MeV (1962RO25). See also (1957CH1A, 1964BA1C, 1965ZH1A, 1967CH04, 1967FU1A). In reaction (c), the angular distributions of ⁸Be nuclei (identified through the α-decay) leading to the ground and 4.4 MeV states of ¹²C have been determined for E_α = 35.5 to 41.9 MeV. The angular distributions and integrated cross sections vary strongly with energy (1965BR13). See also (1962DO1B, 1962ZU01, 1965KU1B, 1965ZE1B, 1967PA1T, 1967TA1C, 1968YA1C).

69. ¹⁶O(d, ⁶Li)¹²C Q_m = -5.689

At E_d = 14.6 MeV, the ground state angular distribution suggests that direct interaction predominates (1964DA1B). Qualitative agreement with DWBA is reported (1966DA1C). See also (1963DR1B, 1964BL1C, 1965SL1C).

70. ¹⁶O(³He, ⁷Be)¹²C Q_m = -5.574

See (1967ZA1B).

71. ¹⁶O(¹⁰B, ¹⁴N)⁴He⁴He⁴He Q_m = -2.822

See (1965SH10, 1966SH1B).

72. ¹⁶O(¹⁴N, ¹⁸F)¹²C Q_m = -2.745

See (1966GA10).

73. ¹⁷O(d, ⁷Li)¹²C Q_m = -2.579

See (1967DE03).

74. ¹⁸O(d, ⁸Li)¹²C Q_m = -8.593

See (1963DE02).

75. ¹⁹F(p, 2α)¹²C Q_m = 0.953

See (1962FO03).