(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).
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 Qm, 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).
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)).
At E(7Li) = 3.2 MeV, the ground state deuteron group and the deuteron groups corresponding to the known levels with Ex < 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 τm < 0.32 and < 0.12 psec, respectively, for 14C*(6.09, 7.01). Eγ = 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).
Resonant structure has been observed in the yield of neutrons at Et = 1.200, 1.340, 1.567, 1.650, 1.700, 1.800, 1.940, 2.055, 2.245 and 2.315 MeV corresponding to Ex = 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).
The angular distributions of ground state protons have been measured for Eα = 2.5 to 5.0 MeV (1963MA28). See also (1959AJ76) and 15N.
At E(7Li) = 5 MeV, α-particle groups are observed to the known states of 14C with Ex < 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 Ex = 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 Ex = 6.09 and 8.32 MeV (1966MC05). See also (1963MI02, 1963MO1B).
Observed proton groups are displayed in Table 14.2 (in PDF or PS). Angular distributions have been observed at Et = 5.5 MeV (1960JA17) and Et = 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.
See (1968HU1H, 1968SC1H, 1969BR1D, 1969SU1E).
The thermal capture cross section is 0.9 ± 0.2 mb (1964ST25), 1.0 ± 0.2 mb (1963MO1C). Two γ-rays are observed with Eγ = 8.174 ± 0.002 and 6.093 ± 0.002 MeV [Ex = 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).
The coherent scattering length (thermal, bound) is 6.0 fm (1961WI1A, 1969BA1P). The total cross section has been measured for En = 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 Jπ = 1+. The peak cross section for the En = 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 En = 2.43 and 2.45 MeV indicate J = 2 and J ≥ 1, respectively (1961CO05). See also (1969HO1Y).
See (1947HU03, 1954SA68, 1964GA1A).
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 Jπ 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 Jπ = 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 Jπ = 0+; τm > 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 Jπ = 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 (τm < 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 Jπ = 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 Jπ = 1- and 3- for the 7.34 MeV state (1958WA02, 1966AL10); the angular correlation data is consistent with Jπ = 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).
At Et = 5.5 MeV, the ground state deuterons have been observed (1961BA10).
At Ed = 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 Ed = 3.4 MeV by (1967NE06). See also (1960WA12). For reaction (a), see (1969CU1D).
See (1968BA1E, 1968CE1C, 1969DA1P).
The weighted mean of five Q-value determinations is 626 ± 1 keV (1957VA11). (1965IS1A) report 621 ± 6 keV. (1969NY1A) report γ-rays with Eγ = 6.082 ± 0.010 (Doppler corrected) and 6.732 ± 0.005 MeV. τm of 14C*(6.09) ≤ 0.3 psec (1969NY1A). See also (1959GA14, 1959HA13, 1963MO04, 1964MO1D, 1967AN08, 1969DI1B), (1959AJ76) and 15N.
The angular distributions of ground state neutrons have been determined at En = 14.1 and 14.8 MeV (1967FE06). See also (1956FR1A).
See 18O in (1959AJ76) and (1965BE1N).
See (1963DR1B, 1964BL1C, DE65C, 1966DA1C, 1966DE09).
See (1968GO1Q) and reaction 10.
Not observed: see (1962LA15).