
^{14}C (1970AJ04)(See Energy Level Diagrams for ^{14}C) 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 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 βdecay rate of ^{14}C and the radiative width of ^{14}N*(2.31) cannot simultaneously be explained by a conventional central force plus spinorbit interaction together with configuration mixing: the nuclear force must include a tensor part (1968RO1C). For other discussions of the long lifetime of ^{14}C, see (1959AJ76) and (1959JA1B, 1962AL1F, 1962VA1F, 1962WE1B, 1964KU1F, 1966ZA03, 1967BL24, 1968FR03, 1969DE16, 1969EL1B, 1969FR1E).
These reactions have been studied with E(^{7}Li) to 6.5 MeV: see (1957NO14, 1957NO17, 1962BE24, 1963CA09, 1963HU02, 1964DZ1A, 1966PI02, 1969CA1A). For E(^{7}Li) = 2.3 to 5.8 MeV, the cross section for emission of α_{0}, α_{1}, α_{2+3+4} (to the first five states of ^{10}Be) 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(^{7}Li) = 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(^{7}Li) = 5.1 MeV, the γdecay of the six bound excited states has been studied by (1966CA07): see Table 14.3 (in PDF or PS). Measurements at E(^{7}Li) = 5.7 MeV give τ_{m} < 0.32 and < 0.12 psec, respectively, for ^{14}C*(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 ^{14}C*(6.73) (1969TH01).
^{†} Angular distributions of the deuterons to ^{14}C*(0, 6.09, 6.59 + 6.73, 6.90 + 7.01, 7.34, 8.32) have been measured at E(^{7}Li) = 5.6, 5.8, 6.0 and 6.2 MeV (1969SN02).
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).
The angular distributions of ground state protons have been measured for E_{α} = 2.5 to 5.0 MeV (1963MA28). See also (1959AJ76) and ^{15}N.
At E(^{7}Li) = 5 MeV, αparticle groups are observed to the known states of ^{14}C with E_{x} < 10 MeV except ^{14}C*(6.90), and to the (unresolved) 10.4 MeV states. There is some indication also of ^{14}C 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 αparticles to the ground state of ^{14}C and to the states at E_{x} = 6.09 and 8.32 MeV (1966MC05). See also (1963MI02, 1963MO1B).
See (1963HO1E).
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 ^{14}C*(6.59, 8.32), the stripping patterns are inconclusive (1964MI05). Particleγ correlations have been studied by (1968BE30): see Table 14.3 (in PDF or PS). The lifetime of ^{14}C*(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 ^{15}N.
See (1968HU1H, 1968SC1H, 1969BR1D, 1969SU1E).
The thermal capture cross section is 0.9 ± 0.2 mb (1964ST25), 1.0 ± 0.2 mb (1963MO1C). Two γrays 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 ^{14}C 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 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; θ^{2} 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).
See (1947HU03, 1954SA68, 1964GA1A).
The weighted mean of reported Qvalues 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 θ^{2}: see Table 14.5 (in PDF or PS) (1955MC75, 1958WA02, 1963LI09, 1966GL01, 1967SC29). See also (1963DE19, 1965LA09) and ^{15}N. Observed γradiation assigned to ^{14}C 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 ^{14}N (1952TH24, 1958CH1A, 1958GO81, 1959CH28, 1959WA04, 1966WA1C). The pγ 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; (pγ) 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 γrays 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 ^{14}C and ^{14}N 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 E_{t} = 5.5 MeV, the ground state deuterons have been observed (1961BA10).
Not reported.
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).
See (1968BA1E, 1968CE1C, 1969DA1P).
The weighted mean of five Qvalue determinations is 626 ± 1 keV (1957VA11). (1965IS1A) report 621 ± 6 keV. (1969NY1A) report γrays with E_{γ} = 6.082 ± 0.010 (Doppler corrected) and 6.732 ± 0.005 MeV. τ_{m} of ^{14}C*(6.09) ≤ 0.3 psec (1969NY1A). See also (1959GA14, 1959HA13, 1963MO04, 1964MO1D, 1967AN08, 1969DI1B), (1959AJ76) and ^{15}N.
See (1968ST1U).
The angular distributions of ground state neutrons have been determined at E_{n} = 14.1 and 14.8 MeV (1967FE06). See also (1956FR1A).
Not reported.
Not reported.
Not reported.
See (1961TA10).
See ^{18}O in (1959AJ76) and (1965BE1N).
See (1963DR1B, 1964BL1C, DE65C, 1966DA1C, 1966DE09).
See (1968GO1Q) and reaction 10.
See (1967DE03).
Not observed: see (1962LA15).
