A=14C (1976AJ04)

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¹⁴C (1976AJ04)

(See Energy Level Diagrams for ¹⁴C)

GENERAL: See also (1970AJ04) and Table 14.3 [Table of Energy Levels] (in PDF or PS).

Nuclear models: (1970FR13, 1970FR1C, 1970KH01, 1971BA2Y, 1972LI06, 1973KU03, 1973SA30, 1975MI12, 1975VE01).

Special reactions involving ¹⁴C: (1969GA18, 1969KR21, 1971AR02, 1972VO06, 1973KO1D, 1973KU03, 1973VO1G, 1973WI15, 1974BE16, 1974KO25, 1975HU14, 1975KU01, 1975UD01).

Reactions involving muons: (1970DM01, 1970VA24, 1973BE16, 1973KI12, 1973MU05, 1973MU11, 1973MU1B, 1974FU1B).

Reactions involving pions (See also reactions 17, 33, 41.): (1970DO04, 1971KO23, 1973DA37, 1973KA1D, 1974LI15, 1975EI1B, 1975HU1D, 1975RE01).

Other topics: (1970FO1B, 1970GU13, 1970KH01, 1970SU1B, 1971BA2Y, 1971JA14, 1971ST40, 1972AN05, 1972CA37, 1973AL1B, 1973GO1H, 1973HO32, 1973KI05, 1973KU03, 1973MA48, 1973PA1F, 1974CA1H, 1974DZ03, 1974HA1C, 1975KU01, 1975MO1M, 1975VE01, 1976MA04).

Ground state: (1974DE1E, 1975BE31).

Mass of ¹⁴C: 14.003241983 (12) amu (1975SM02).

1. ¹⁴C(β^-)¹⁴N Q_m = 0.1561

Measured τ_1/2 are 5745 ± 50 y (1961MA1L, 1961MA32, 1964HU09), 5780 ± 65 y (1961WA16), 5680 ± 40 y (1962OL04), 5660 ± 30 y (1968BE47), 5736 ± 56 y (1972EM01): the recommended value of τ_1/2 = 5730 ± 40 y ^†. Using Q_m, log ft = 9.02 (1969KA1B). The spectrum does not deviate from the allowed shape down to 3 keV (1954MO84). The large log ft difference between this and the mirror transition in ¹⁴O(β⁺) cannot be accounted for by the differences in the binding energies of ¹⁴C and ¹⁴O (1972WI05). For other discussions of the long lifetime of ¹⁴C see (1959AJ76, 1970AJ04) and (1976GOZX). See also (1970SO08) and (1969EL1A, 1970FR13, 1971HU10, 1973HA49, 1973KU1J, 1974ZA1G; theor.).

^† (W. Mann, private communication.)

2. (a) ⁷Li(⁷Li, 2n)¹²C Q_m = 13.674 E_b = 26.797
(b) ⁷Li(⁷Li, n)¹³C Q_m = 18.620
(c) ⁷Li(⁷Li, p)¹³B Q_m = 5.966
(d) ⁷Li(⁷Li, d)¹²B Q_m = 3.311
(e) ⁷Li(⁷Li, t)¹¹B Q_m = 6.199
(f) ⁷Li(⁷Li, α)¹⁰Be Q_m = 14.784
(g) ⁷Li(⁷Li, ⁸Be)⁶He Q_m = 7.278
(h) ⁷Li(⁷Li, ⁷Li)⁷Li

These reactions have been studied with E(⁷Li) to 6.5 MeV: see (1970AJ04) for the earlier references. For E(⁷Li) = 2.3 to 5.8 MeV, the cross section for emission of α₀, α₁ and α₂₊₃₊₄ is found to increase monotonically with energy (1964DZ1A, 1969CA1A). However, (1971WY01) reports several broad structures in the 0° yield of α₀ and α₁ for E(⁷Li) = 2 to 20 MeV: it is suggested that these are neither compound nucleus resonances nor Ericson-type fluctuations but that they are due to a forward-direction cluster transfer process (1971WY01).

3. ⁹Be(⁶Li, p)¹⁴C Q_m = 15.127

Observed proton groups are displayed in Table 14.4 (in PDF or PS) (1973AJ01). Angular distributions have been measured at E(⁶Li) = 1.9 MeV (1969KO1A: p₀, p₁, p_2+3+4+5, p₆, p₇, p₈) and at 20 MeV ((1973AJ01) and unpublished results: to most states shown in Table 14.4 (in PDF or PS)). See also ¹⁵N.

4. ⁹Be(⁷Li, d)¹⁴C Q_m = 10.101

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). Angular distributions for the d₀ group have also been measured at E(⁷Li) = 1.7 to 1.9 MeV (1969KA1C). The γ-decay of six bound excited states has been studied by (1966CA07). (1969TH01) report E_γ = 6094.5 ± 3.2, 6728.1 ± 1.4 and 7011.7 ± 5.2 keV for the ground state transitions of these states and τ_m < 120 fsec for ¹⁴C*(7.01).

5. ⁹Be(¹³C, ⁸Be)¹⁴C Q_m = 6.512

At E(¹³C) = 9 MeV ¹⁴C*(6.09, 6.73, 6.90) have been populated: τ_m < 10, > 5 × 10⁴ and 36 ± 4 fsec, respectively (1975SE04). See also (1975SE03).

6. ¹⁰Be(α, p)¹³B Q_m = -8.818 E_b = 12.013

The yield of 3.7 MeV γ-rays coincident with E_β > 4 MeV (from the ¹³B decay) has been measured for E_α = 13.6 to 17 MeV: a strong interference anomaly is observed which appears to correspond to E_x = 23.624 ± 0.036 MeV, Γ_c.m. = 120⁺¹²⁰_-60 keV. It is suggested that it is a T = 2 state whose analog is either ¹⁴B*(0.74) or (1.38) (1974GO1T).

7. ¹¹B(t, n)¹³C Q_m = 12.4214 E_b = 20.5984

Resonant structure has been reported in the yield of neutrons with E_t = 1.20 to 2.32 MeV: these are thought to correspond to ten excited states in ¹⁴C in the range 21.54 < E_x < 22.42 MeV (1965VA13).

8. ¹¹B(α, p)¹⁴C Q_m = 0.7837

Angular distributions of p₀ have been measured at E_α = 1.43 to 2.94 MeV (1976DA1U), 2.5 to 5.0 MeV (1963MA28) and 10.8 to 25.1 MeV (1969SP02). See also (1967SP09), (1971BU1K; theor.) and ¹⁵N.

9. ¹¹B(⁷Li, α)¹⁴C Q_m = 18.132

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 - 10.5 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). Angular distributions have been obtained for the α-particles to ¹⁴C*(0, 6.09, 8.32) (1966MC05).

10. ¹²C(t, p)¹⁴C Q_m = 4.6412

Observed proton groups are displayed in Table 14.5 (in PDF or PS). Angular distributions have been measured at E_t = 5.5 MeV (1960JA17), 8 to 13 MeV (1964MI05) [see Table 14.5 (in PDF or PS)] and at 16 and 20 MeV (1972KE02: p₀). Particle-gamma correlations have been studied by (1968BE30): see Table 14.6 (in PDF or PS). The lifetime of ¹⁴C*(6.73) is 97 ± 15 psec; the (6.73 → 0) E3 transition is enhanced by 3.3 ± 0.8 W.u. (1968AL12). The nuclear gyromagnetic ratio for ¹⁴C*(6.73) is g = 0.272 ± 0.007 showing that the state is not of a pure (p^-3_1/2d_5/2) configuration (1974AL07).

See also (1969AR1B), (1974BA65; theor.) and ¹⁵N.

11. ¹²C(¹²C, ¹⁰C)¹⁴C Q_m = -18.723

At E(¹²C) = 114 MeV ¹⁴C*(6.73, 10.25) [J^π = 3^- and 4⁺, respectively] are populated (1972SC21, 1974AN36). See also (1971SC1F, 1972MO1E, 1973SC1J).

12. (a) ¹²C(¹⁴N, ¹²N)¹⁴C Q_m = -17.500
(b) ¹²C(¹⁸O, ¹⁶O)¹⁴C Q_m = 0.934

For reaction (b) see (1970BA1J, 1974CH1Q). See also (1970AJ04), (1974GO1L) and (1970AN1D, 1971AL1D, 1971RO1G, 1972RO35, 1975TA02; theor.). For reaction (a) see (1975NA11).

13. ¹³C(n, γ)¹⁴C Q_m = 8177.0
Q₀ = 8176.575 ± 0.030 keV (1975SM02).

The thermal capture cross section is 0.9 ± 0.2 mb (1973MU14). The neutron capture yield has been measured for E_n = 95 to 235 keV. The parameters for ¹⁴C*(8.32) are E_n = 152 ± 1 keV, Γ_n = 5 ± 1 keV, Γ_γ = 4.0 ± 1.6 eV [see Table 14.7 (in PDF or PS)]. The calculated cross section for kT = 30 keV is 0.12 ± 0.04 mb suggesting that ¹³C is not significantly involved as a neutron poison in s-process nucleosynthesis (1971AL09). See also (1970CL1C, 1973CL1E; astrophys. questions). 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).

14. ¹³C(n, n)¹³C E_b = 8.170

The coherent scattering length (thermal, bound) is 6.0 ± 0.2 fm (1973MU14). The total cross section has been measured for E_n = 0.10 to 9 MeV and 16 to 23 MeV: observed resonances are displayed in Table 14.7 (in PDF or PS) (1961CO05, 1975HE02). See also (1973MU14).

15. ¹³C(n, t)¹¹B Q_m = -12.4214 E_b = 8.1770

See (1973BI1B).

16. ¹³C(n, α)¹⁰Be Q_m = -3.836 E_b = 8.1770

See (1970AJ04).

17. ¹³C(p, π⁺)¹⁴C Q_m = -132.174

At E_p = 185 MeV, an angular distribution has been measured for the transition to ¹⁴C_g.s.: it is forward peaked and goes through a minimum at 90° [while the π^- to ¹⁴O_g.s. show a flat distribution: see reaction 6 in ¹⁴O]. There is evidence also for the population of ¹⁴C*(6.09, 8.32, 14.9 ± 0.2) as well as some other structure (1973DA37). See also (1970DO04).

18. ¹³C(d, p)¹⁴C Q_m = 5.9524

Observed proton groups are displayed in Table 14.8 (in PDF or PS). Angular distributions have been measured at a number of energies up to E_d = 14.8 MeV: recent measurements have been carried out for the p₀ group at E_p = 0.41 to 0.81 MeV (1971PU01) and 12.1 to 14.0 MeV (1969GU1C; prelim. results). See also (1970LI1E, 1971LI1K, 1975ZA06). For listings of θ²_n see Table 14.5 (in PDF or PS) in (1970AJ04).

Gamma rays are exhibited in Table 14.6 (in PDF or PS): studies of these, of the angular distributions analyzed by DWBA, and of pγ correlations lead to the following J^π assignments [see reaction 14 in (1970AJ04) for a full discussion of the evidence and of the relevant references]. ¹⁴C*(6.09) is 1^- (decay is E1); ¹⁴C*(6.59) is 0⁺ (internal pairs only); ¹⁴C*(6.73) is 3^- (γ₀ is E3; l_n = 2); ¹⁴C*(6.90) is 0^- (no γ₀; 0.81 MeV cascade via 6.09 is predominantly dipole; γ_0.8 + γ_6.1 correlation is consistent with J = 0, and plane polarization leads to negative parity); ¹⁴C*(7.34) is 2^- (strength of cascade decay and angular correlation results): see, in particular, (1958WA02, 1965LA09, 1966AL10,, 1966RI02, 1966WA1C). τ_m < 15 fsec (1974RU1B), < 40 fsec (1973RE1E, 1973RE1F; prelim. results) for ¹⁴C*(6.09). See also (1967SP09) and ¹⁵N.

19. ¹³C(t, d)¹⁴C Q_m = 1.9194

See (1961BA10).

20. ¹³C(⁷Li, ⁶Li)¹⁴C Q_m = 0.926

At E(⁷Li) = 34 MeV the angular distribution has been measured for the ground state transition. ¹⁴C*(6.09, 6.73) and possibly other states are also populated (1973SC26).

21. ¹³C(¹¹B, ¹⁰B)¹⁴C Q_m = -3.279

At E(¹¹B) = 114 MeV ¹⁴C_g.s. is weakly excited but ¹⁴C*(6.73, 7.34) [J^π = 3^- and 2^-, respectively] are strongly populated (1974AN36). See also (1972MO1E, 1973SC1J).

22. (a) ¹³C(¹⁴N, ¹³N)¹⁴C Q_m = -2.377
(b) ¹³C(¹⁵N, ¹⁴N)¹⁴C Q_m = -2.657

See (1971GA05) and (1973TO05; theor.) for reaction (a). For reaction (b) see ¹⁴N, reaction 60 (1975GA17).

23. (a) ¹³C(¹⁷O, ¹⁶O)¹⁴C Q_m = 4.035
(b) ¹³C(¹⁸O, ¹⁷O)¹⁴C Q_m = 0.130

See (1974CH1Q).

24. ¹⁴B(β^-)¹⁴C Q_m = 20.64

¹⁴B decays primarily to ¹⁴C*(6.09, 6.73): see Table 14.2 (in PDF or PS). τ_1/2 = 16.1 ± 1.2 msec (1974AL11).

25. ¹⁴C(γ, n)¹³C Q_m = -8.1770

See (1973KI05; theor.).

26. ¹⁴C(e, e)¹⁴C

The elastic scattering has been studied at E_e = 374.6 MeV: the charge radius r_rms = 2.56 ± 0.05 fm (1973KL12). At E_e = 101.2 MeV, ¹⁴C*(7.01, 8.32) [both J^π = 2⁺] are excited strongly: Γ_γ = 50.8 ± 7.1 and 4.1 ± 1.7 meV (1972CRZN; prelim. results). There is some evidence also for excitation of other states of ¹⁴C including ¹⁴C*(9.8, 11.3) (1973CR1B; prelim. results; see also (1975FA1A)), however, there is no evidence of sharp structure in the region E_x = 19 to 24 MeV where the T = 2 analog state of ¹⁴B_g.s. would be expected (1974KL12: E_e = 61.5 and 80.7 MeV). See also (1973FA1K, 1974DE1E).

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

The elastic angular distribution has been measured by (1971CU01) at E_p = 14.5 MeV (reaction (a)) and by (1967NE06) at E_d = 3.4 MeV (reaction (b)). The population of ¹⁴C*(6.09, 6.58, 6.72, 7.01 ± 0.02, 7.34, 8.32, 9.80, 10.5) has been reported by (1959AR1A) at E_d = 14.9 MeV. Angular distributions have also been studied at E_d = 17 MeV to ¹⁴C*(0, 6.73, 7.01) (1975CE04).

28. ¹⁴C(³He, ³He)¹⁴C

The elastic angular distribution has been measured at E(³He) = 10, 12, 15 and 18 MeV (1970DU07). See also (1971CO14).

29. ¹⁴C(α, α)¹⁴C

Elastic angular distributions have been studied at E_α = 22, 24 and 28 MeV (1972OE01, 1973OE01).

30. (a) ¹⁴C(¹²C, ¹²C)¹⁴C
(b) ¹⁴C(¹³C, ¹³C)¹⁴C

The elastic scattering for reaction (a) has been studied at E(¹²C) = 12, 15, 18 and 20 MeV and for reaction (b) at 15 MeV (1972BO68). See also (1973FE03), (1974GO1L) and (1973MC1J, 1973VO04, 1975DE09, 1975VO1B; theor.).

31. ¹⁴C(¹⁴N, ¹⁴N)¹⁴C

See (1971BO1U) and (1971VO1D, 1975DE09, 1975VO1B; theor.).

32. ¹⁴C(¹⁶O, ¹⁶O)¹⁴C

The elastic scattering angular distributions have been measured at E(¹⁶O) = 20, 25 and 30 MeV (1974KO1P).

33. ¹⁴N(π^-, γ)¹⁴C Q_m = 139.413

Branching ratios have been measured for the capture of stopped pions to ¹⁴C*(0, 7.0 ± 0.1, 8.3, 11.3, 20.0 ± 1.0) (1975BA52): the total radiative capture branching is 2.1 ± 0.2%.

34. ¹⁴N(n, p)¹⁴C Q_m = 0.6263

¹⁴C*(6.09) decays with E_γ = 6098 ± 5 keV, τ_m < 0.1 psec (1972NY02), and E_γ = 6732 ± 5 keV from the decay of ¹⁴C*(6.73) (1971NY03). The p₀ angular distribution has been measured at E_n = 14 MeV (1971CO32). See also (1970AJ04), (1970DI1A), (1973CL1E; astrophys. questions) and ¹⁵N.

35. ¹⁴N(t, ³He)¹⁴C Q_m = -0.1375

See (1970AJ04).

36. ¹⁴N(⁷Li, ⁷Be)¹⁴C Q_m = -1.018

See (1971BAWQ).

37. (a) ¹⁵N(γ, p)¹⁴C Q_m = -10.2073
(b) ¹⁵N(e, e'p)¹⁴C Q_m = -10.2073

For E_bs = 19.6 to 38.3 MeV ¹⁴C is reported to be formed preferentially in the ground state and in excited states with E_x = 7.0 ± 0.2 and 10.7 MeV (1971DE42). See also (1973DE30) and ¹⁵N. For reaction (b) see (1975MU07).

38. ¹⁵N(n, d)¹⁴C Q_m = -7.9827

The angular distributions of n₀ have been measured at E_n = 14.1 and 14.8 MeV (1967FE06, 1971MI12).

39. ¹⁵N(d, ³He)¹⁴C Q_m = -4.7136

¹⁴C states populated in this reaction at E_d = 52 MeV are displayed in Table 14.9 (in PDF or PS). The table also shows the l-values obtained from the analysis of the angular distributions (1971KA35).

40. ¹⁵N(t, α)¹⁴C Q_m = 9.6073

Angular distributions of the α₀ group have been measured at E_t = 0.82 to 1.62 MeV (1973AB1E). See also ¹⁸O in (1978AJ03).

41. ¹⁶O(π^-, np)¹⁴C Q_m = 121.188

At E_π^- = 230 MeV, γ-rays from the population of ¹⁴C*(6.73, 6.90) are observed (1974LI15). See also (1971KO23).

42. ¹⁶O(⁶Li, ⁸B)¹⁴C Q_m = -16.591

See (1973CE1B).

43. ¹⁶O(¹¹B, ¹³N)¹⁴C Q_m = -4.434

See (1972KU1H; theor.).

44. ¹⁶O(¹⁸O, ²⁰Ne)¹⁴C Q_m = -1.497

Angular distributions are reported at E(¹⁸O) = 28 and 32 MeV (1971BA68).

45. ¹⁷O(n, α)¹⁴C Q_m = 1.819

See ¹⁸O in (1978AJ03) and (1973CL1E; astrophys. relevance).

46. ¹⁸O(d, ⁶Li)¹⁴C Q_m = -4.754

See (1975BE01), (1970AJ04) and (1974DO03; theor.).

47. ¹⁹F(d, ⁷Be)¹⁴C Q_m = -7.140

See (1967DE03).

48. ²²Ne(α, ¹²C)¹⁴C Q_m = -8.6201

Not observed: see (1962LA15).