A=14C (1970AJ04)

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¹⁴C (1970AJ04)

(See Energy Level Diagrams for ¹⁴C)

GENERAL: See Table 14.1 [Table of Energy Levels] (in PDF or PS).

See (1954JA1A, 1956EL1B, 1957VI1A, 1958BA1A, 1959OT1A, 1959SK1A, 1960TA1C, 1960WA12, 1961BA1F, 1961FR1C, 1962TA1E, 1963BL1B, 1963NA04, 1963SO04, 1963VL1A, 1964LI1B, 1964LO1B, 1965BA1X, 1965KO1D, 1965WA1J, 1965ZA1B, 1966BA42, 1966BO1R, 1966GU08, 1966MI1G, 1966ZA03, 1967GR1D, 1967HA10, 1967IN1B, 1967KO1N, 1967KO1F, 1968EI1C, 1968FA1B, 1968FR03, 1968NE1C, 1968RO1C, 1969AR13, 1969AT1A, 1969FR1E, 1969SH1A, 1969SO08, 1969SO1E).

1. ¹⁴C(β^-)¹⁴N Q_m = 0.156

Recent values are 5745 ± 50 y (1961MA1L, 1961MA32, 1964HU09), 5780 ± 65 y (1961WA16), 5680 ± 40 y (1962OL04), 5660 ± 30 y (1968BE47), leading to a weighted mean of 5692 ± 21 y. See also (1962GO33). Using Q_m, log ft = 9.03 (1966BA1A), 9.02 (1969KA1B). The spectrum does not deviate from the allowed shape down to 3 keV (1954MO84). The β-decay rate of ¹⁴C and the radiative width of ¹⁴N*(2.31) cannot simultaneously be explained by a conventional central force plus spin-orbit interaction together with configuration mixing: the nuclear force must include a tensor part (1968RO1C). For other discussions of the long lifetime of ¹⁴C, see (1959AJ76) and (1959JA1B, 1962AL1F, 1962VA1F, 1962WE1B, 1964KU1F, 1966ZA03, 1967BL24, 1968FR03, 1969DE16, 1969EL1B, 1969FR1E).

2. (a) ⁷Li(⁷Li, 2n)¹²C Q_m = 13.672 E_b = 26.795
(b) ⁷Li(⁷Li, n)¹³C Q_m = 18.619
(c) ⁷Li(⁷Li, p)¹³B Q_m = 5.964
(d) ⁷Li(⁷Li, d)¹²B Q_m = 3.309
(e) ⁷Li(⁷Li, t)¹¹B Q_m = 6.197
(f) ⁷Li(⁷Li, α)¹⁰Be Q_m = 14.783
(g) ⁷Li(⁷Li, ⁸Be)⁶He Q_m = 7.272
(h) ⁷Li(⁷Li, ⁷Li)⁷Li

These reactions have been studied with E(⁷Li) to 6.5 MeV: see (1957NO14, 1957NO17, 1962BE24, 1963CA09, 1963HU02, 1964DZ1A, 1966PI02, 1969CA1A). For E(⁷Li) = 2.3 to 5.8 MeV, the cross section for emission of α₀, α₁, α₂₊₃₊₄ (to the first five states of ¹⁰Be) increases monotonically with energy (1964DZ1A, 1969CA1A). The measured cross sections for reactions (c), (d), (e) and (f) indicate that the reactions probably occur by a mixture of compound nucleus and direct reaction mechanisms. The Coulomb field appears to have a marked effect on the cross sections (1969CA1A: see also (1963HU02)).

3. ⁹Be(⁶Li, p)¹⁴C Q_m = 15.130

See (1967SE08) and ¹⁵N.

4. ⁹Be(⁷Li, d)¹⁴C Q_m = 10.102

At E(⁷Li) = 3.2 MeV, the ground state deuteron group and the deuteron groups corresponding to the known levels with E_x < 9 MeV have been observed (1964CA05)^†. At E(⁷Li) = 5.1 MeV, the γ-decay of the six bound excited states has been studied by (1966CA07): see Table 14.3 (in PDF or PS). Measurements at E(⁷Li) = 5.7 MeV give τ_m < 0.32 and < 0.12 psec, respectively, for ¹⁴C*(6.09, 7.01). E_γ = 6.0945 ± 0.0032, 6.7281 ± 0.0014 and 7.0117 ± 0.0052 MeV for the ground state transitions for these two levels and ¹⁴C*(6.73) (1969TH01).

^† Angular distributions of the deuterons to ¹⁴C*(0, 6.09, 6.59 + 6.73, 6.90 + 7.01, 7.34, 8.32) have been measured at E(⁷Li) = 5.6, 5.8, 6.0 and 6.2 MeV (1969SN02).

5. (a) ¹¹B(t, n)¹³C Q_m = 12.422 E_b = 20.598
(b) ¹¹B(t, α)¹⁰Be Q_m = 8.586

Resonant structure has been observed in the yield of neutrons at E_t = 1.200, 1.340, 1.567, 1.650, 1.700, 1.800, 1.940, 2.055, 2.245 and 2.315 MeV corresponding to E_x = 21.540, 21.650, 21.828, 21.893, 21.933, 22.011, 22.121, 22.211, 22.360 and 22.415 MeV (1965VA13; natural B target). For reaction (b) see (1967SI1F).

6. ¹¹B(α, p)¹⁴C Q_m = 0.784

The angular distributions of ground state protons have been measured for E_α = 2.5 to 5.0 MeV (1963MA28). See also (1959AJ76) and ¹⁵N.

7. ¹¹B(⁷Li, α)¹⁴C Q_m = 18.131

At E(⁷Li) = 5 MeV, α-particle groups are observed to the known states of ¹⁴C with E_x < 10 MeV except ¹⁴C*(6.90), and to the (unresolved) 10.4 MeV states. There is some indication also of ¹⁴C states at (10.71), 11.35, 11.66, (14.15), (14.73) and (15.07) MeV (± approx. 50 keV), in addition to the 12 MeV states. The wide state at E_x = 11.9 MeV is not observed. Angular distributions have been obtained for the α-particles to the ground state of ¹⁴C and to the states at E_x = 6.09 and 8.32 MeV (1966MC05). See also (1963MI02, 1963MO1B).

8. ¹¹B(¹⁹F, ¹⁶O)¹⁴C Q_m = 8.899

See (1963HO1E).

9. ¹²C(t, p)¹⁴C Q_m = 4.641

Observed proton groups are displayed in Table 14.2 (in PDF or PS). Angular distributions have been observed at E_t = 5.5 MeV (1960JA17) and E_t = 8 to 13 MeV (1964MI05). Aside from the ground state and groups corresponding to ¹⁴C*(6.59, 8.32), the stripping patterns are inconclusive (1964MI05). Particle-γ correlations have been studied by (1968BE30): see Table 14.3 (in PDF or PS). The lifetime of ¹⁴C*(6.73) is 97 ± 15 psec (1968AL12). The (6.73 → 0) E3 transition is enhanced by 3.3 ± 0.8 W.u. (1968AL12).

See also (1960MU07, 1962GU01, 1962KU09, 1967KE1J, 1969ET01), (1964AB1B, 1965GL07, 1965SH1E, 1966GL1C, 1966SH1F, 1967TI1B, 1969SO08; theor.), (1959AJ76) and ¹⁵N.

10. ¹²C(¹⁸O, ¹⁶O)¹⁴C Q_m = 0.934

See (1968HU1H, 1968SC1H, 1969BR1D, 1969SU1E).

11. ¹³C(n, γ)¹⁴C Q_m = 8.176
Q₀ = 8.177 ± 0.002 (1967TH05).

The thermal capture cross section is 0.9 ± 0.2 mb (1964ST25), 1.0 ± 0.2 mb (1963MO1C). Two γ-rays are observed with E_γ = 8.174 ± 0.002 and 6.093 ± 0.002 MeV [E_x = 6.094 ± 0.002 MeV], with intensities of 87 ± 5 and 13 ± 1%. Intensities of transitions via other ¹⁴C states are < 2% (1967TH05). See also (1968FO1A).

12. ¹³C(n, n)¹³C E_b = 8.176

The coherent scattering length (thermal, bound) is 6.0 fm (1961WI1A, 1969BA1P). The total cross section has been measured for E_n = 0.11 to 9 MeV and 16 to 23 MeV. The observed resonances are listed in Table 14.4 (in PDF or PS). For the 153 keV resonance, the shape excludes l = 0; θ² for l = 2 would be 2.3, thus l = 1. The peak cross section is too large for J = 0, but lower than expected for J = 1: it is concluded that J^π = 1⁺. The peak cross section for the E_n = 1.75 MeV level is in excellent agreement with J = 1. Formation by l = 0 is excluded by the shape, but l = 1, 2 remain as possibilities. Peak cross sections for the states at E_n = 2.43 and 2.45 MeV indicate J = 2 and J ≥ 1, respectively (1961CO05). See also (1969HO1Y).

13. ¹³C(n, α)¹⁰Be Q_m = -3.836 E_b = 8.176

See (1947HU03, 1954SA68, 1964GA1A).

14. ¹³C(d, p)¹⁴C Q_m = 5.952

The weighted mean of reported Q-values is 5.948 ± 0.003 MeV: see (1965RY01).

Proton groups reported by (1954SP01, 1955MC75, 1961JA23) are displayed in Table 14.5 (in PDF or PS). See also (1961TE02). Angular distributions have been analyzed by PWBA and DWBA and have led to J^π assignments and to determinations of θ²: see Table 14.5 (in PDF or PS) (1955MC75, 1958WA02, 1963LI09, 1966GL01, 1967SC29). See also (1963DE19, 1965LA09) and ¹⁵N.

Observed γ-radiation assigned to ¹⁴C is exhibited in Table 14.6 (in PDF or PS) (1955BE62, 1955MA36, 1958RA13, 1958WA02, 1965LA09, 1966AL10) and in Table 14.3 (in PDF or PS). The internally formed positron distribution shows that the decay of the 6.09 MeV level is E1 and hence that it has J^π = 1^-; it is presumably the analog of the 8.06 MeV level in ¹⁴N (1952TH24, 1958CH1A, 1958GO81, 1959CH28, 1959WA04, 1966WA1C). The p-γ correlation is isotropic, consistent with l = 0 formation (1963LI09, 1965LA09). The 6.59 MeV state is observed in internal pairs but not in external pair formation. The transition to the ground state is E0, therefore J^π = 0⁺; τ_m > 0.6 psec (1963AL21, 1964WA05, 1966AL10). The mean lifetime of the 6.73 MeV state is greater than 2 psec (1966AL10) [see also reaction 9] and study of the internal pairs suggests that the ground state transition is E3 (1964WA05, 1966WA1C). The stripping pattern is rather clearly l = 2; (p-γ) angular correlations are consistent with J^π = 3^-: J = 1 and 2 are ruled out (1965LA09): see also (1966AL10).

The 0.81 MeV cascade transition from the 6.90 MeV state shows a Doppler shift (τ_m < 0.3 psec) and hence is predominantly dipole. The angular correlation of 6.1 and 0.8 MeV γ-rays is consistent with J = 0 and excludes J = 1 or 2. J = 0 is also suggested by the absence of the direct ground state decay of the 6.90 MeV level (1958WA02). The plane polarization of the 0.81 MeV cascade has been measured in coincidence with the 6.09 MeV ground state transition: the parity of the 6.90 MeV state is negative (1966RI02).

Protons leading to the 7.34 MeV state exhibit a clear l = 2 pattern: therefore J^π = 1^-, 2^- or 3^-. The level decays via cascades through the 6.09 (1^-) and 6.73 (3^-) states: see Table 14.3 (in PDF or PS) (1958RA13, 1958WA02, 1965LA09, 1966AL10). The strength of the cascade (7.34 - 6.09) compared to the ground state transition argues against J^π = 1^- and 3^- for the 7.34 MeV state (1958WA02, 1966AL10); the angular correlation data is consistent with J^π = 2^- and excludes J = 3 (1965LA09). Comparison of reduced widths and calculations of level shifts suggests the following associations of ¹⁴C and ¹⁴N levels: 6.09 - 8.06, 6.59 - 8.62, 6.73 - 8.91, 6.90 - 8.80, (7.01 - 9.17), 7.34 - 9.51 and (8.32 - 10.43) (1960WA12). See also (1959KU1C).

15. ¹³C(t, d)¹⁴C Q_m = 1.919

At E_t = 5.5 MeV, the ground state deuterons have been observed (1961BA10).

16. ¹³C(α, ³He)¹⁴C Q_m = -12.402

Not reported.

17. ¹³C(¹¹B, ¹⁰B)¹⁴C Q_m = -3.280

See (1967PO13, 1969BR1D).

18. (a) ¹⁴C(p, p')¹⁴C*
(b) ¹⁴C(d, d')¹⁴C*

At E_d = 14.9 MeV, inelastic deuteron groups have been seen to the states at 6.09, 6.58, 6.72, 7.01 ± 0.02, 7.34, 8.32, 9.80 and 10.5 MeV (1959AR1A). An angular distribution of elastically scattered deuterons has been obtained at E_d = 3.4 MeV by (1967NE06). See also (1960WA12). For reaction (a), see (1969CU1D).

19. ¹⁴C(³He, ³He)¹⁴C

See (1968BA1E, 1968CE1C, 1969DA1P).

20. ¹⁴N(n, p)¹⁴C Q_m = 0.626

The weighted mean of five Q-value determinations is 626 ± 1 keV (1957VA11). (1965IS1A) report 621 ± 6 keV. (1969NY1A) report γ-rays with E_γ = 6.082 ± 0.010 (Doppler corrected) and 6.732 ± 0.005 MeV. τ_m of ¹⁴C*(6.09) ≤ 0.3 psec (1969NY1A). See also (1959GA14, 1959HA13, 1963MO04, 1964MO1D, 1967AN08, 1969DI1B), (1959AJ76) and ¹⁵N.