
^{14}C (1981AJ01)(See Energy Level Diagrams for ^{14}C) GENERAL: See also (1976AJ04) and Table 14.3 [Table of Energy Levels] (in PDF or PS). Nuclear models: (1976VO1C). Special levels: (1978AL1T, 1979HOZW). Special reactions involving ^{14}C: (1976AB04, 1976BU16, 1976LE1F, 1977AR06, 1978AB08, 1978GE1C, 1978HE1C, 1978KA23, 1978KO01, 1978LE15, 1978TU06, 1979AL22, 1979BO22). Giant resonance: (1979DO17, 1979KI11). Astrophysical questions: (1976DE1G, 1976LI1K, 1977BR1N, 1977CO1U, 1977HA1L, 1977KU1J, 1978BU1B, 1979DE1V, 1979OL1B, 1980ST1C). Muon and neutrino capture and reactions: (1977GO13, 1978DE15, 1979GO1M, 1980LO07, 1980MU1B). Pion and kaon capture and reactions (See also reactions 19, 36 and 44.): (1976DI11, 1976DI10, 1976EN02, FI76F, 1977DO06, 1977RI1H, 1978DA1A, 1978SH16, 1979KI11, 1980ER01, 1980FI05). Applied work: (1976LI1K, 1977ME1D, 1977MU1B, 1977RY1A, 1978AI1A, 1978BE2D, 1978DO1G, 1978HE1M, 1978MU1E, 1979BE2J, 1979GO1L, 1979LI1C, 1979MU1E, 1979ST1P, 1979TA1N, 1980GO1B). Other topics: (1976ST13, 1978DA1A, 1978GA1C, 1978PO1A, 1978SO1A, 1979KA13). Ground state of ^{14}C: (1976BE1G, 1977AN21, 1978AN07, 1978HE1D, 1978NA07, 1978SM02, 1978TA09).
The adopted value of the halflife is 5730 ± 40 y: see (1976AJ04). Using Q_{m}, log ft = 9.04 (1971GO40). For discussions of the lifetime of ^{14}C see (1959AJ76, 1970AJ04, 1976AJ04). See also (1978MA1P), (1976BE1E), (1980RO1D; applied) and (1977GO13, 1977IK1B, 1977RI08, 1979DE15, 1979FE1E, 1979PR1D, 1980LO07; theor.).
These reactions have been studied with E(^{7}Li) to 6.5 MeV: see (1970AJ04) for the early references. For E(^{7}Li) = 2.3 to 5.8 MeV, the cross section for emission of α_{0}, α_{1} and α_{2+3+4} is found to increase monotonically with energy (1964DZ1A, 1969CA1A). However, (1971WY01) reports several broad structures in the 0° yield of α_{0} and α_{1} for E(^{7}Li) = 2 to 20 MeV: it is suggested that these are neither compound nucleus resonances nor Ericsontype fluctuations but that they are due to a forwarddirection cluster transfer process (1971WY01). For reaction (f) see (1978NO1F: 2.0 → 5.5 MeV).
Observed proton groups are displayed in Table 14.6 (in PDF or PS) (1973AJ01). See also (1976AJ04) and ^{15}N.
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). (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. See also (1976AJ04).
At E(^{9}Be) = 5 MeV ^{14}C*(0, 6.09, 6.6, 6.9, 7.34, 8.32, 9.80) are populated. The α_{0} angular distributions have been measured at 5 and 12 MeV (1977YO02).
τ_{m} for ^{14}C*(6.09, 6.73, 6.90) are < 10, > 5 × 10^{4} and 36 ± 4 fsec, respectively (1975SE04): see Table 14.4 (in PDF or PS).
A preliminary report of a resonance corresponding to a T = 2 state has not been published: see (1976AJ04).
For possible resonant structure in (a) see (1976AJ04). For reaction (b) see (1977CI1A).
Angular distributions of p_{0} have been measured at E_{α} = 1.43 to 25.1 MeV [see (1976AJ04)] and at E_{α} = 1.43 to 2.94 MeV (1976DA06) and 4.4 to 6.7 MeV (1978HO08). See also Table 14.4 (in PDF or PS), ^{15}N and (1976EP1A, 1980DO1C; astrophys.).
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  10.5 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). Angular distributions have been obtained for the αparticles to ^{14}C*(0, 6.09, 8.32) (1966MC05).
Observed proton groups are displayed in Table 14.7 (in PDF or PS). Angular distributions have been measured at E_{t} = 5.5 to 23 MeV: see (1976AJ04) and Table 14.6 (in PDF or PS) (1978AJ02, 1978MO07, 1978MO08, 1979PI01). (1978FO06) report that a calculation which treats the positive parity states of ^{14}C as (sd)^{2} twoneutron states coupled to an inert ^{12}C core gives good agreement with the (t, p) strengths and the experimental E_{x}. τ_{m} of ^{14}C*(6.73) is 97 ± 15 psec (1968AL12); the nuclear gyromagnetic ratio is g = 0.272 ± 0.007 showing that the state is not of a pure (p^{3}_{1/2}d_{5/2}) configuration (1974AL07). See also (1977FO1E) and ^{15}N.
At E_{α} = 65 MeV ^{14}C*(6.73, 10.74) are strongly populated. Angular distributions are measured to ^{14}C*(0, 6.73, 10.74, 14.9 ± 0.1): the distribution to ^{14}C*(10.74) is consistent with L = 4 (1976JA13, 1978JA10). See also (1976CE1E).
At E(^{10}B) = 100 MeV ^{14}C*(6.72, 10.74) are strongly populated and the angular distributions to these states are reported. ^{14}C*(15.0) is also observed (1978HA10).
At E(^{12}C) = 114 MeV ^{14}C*(6.73, 10.25) [3^{} and 4^{+}, respectively] are populated (1972SC21, 1974AN36).
For reaction (a) see (1976AJ04). At E(^{16}O) = 128 MeV angular distributions are reported to ^{14}C*(0, 6.73, 10.74) [J^{π} = 0^{+}, 3^{}, 4^{+}] (1979PR07). For reaction (c) see (1976WE05) and (1976AJ04). See also (1976KA04; theor.).
The thermal capture cross section is 0.9 ± 0.2 mb (1973MU14, 1974SH1E). The neutron capture yield has been measured from E_{n} = 95 to 235 keV: see Table 14.8 (in PDF or PS). The (n, γ_{0}) cross section has also been measured for E_{n} = 5.6 to 14.0 MeV (1980JE1A). ^{13}C is probably not significantly involved as a neutron poison in sprocess nucleosynthesis: see (1976AJ04). Two γrays are observed in thermal neutron capture with E_{γ} = 8174 ± 2 and 6093 ± 2 keV [E_{x} = 6094 ± 2 keV], with intensities of 87 ± 5 and 13 ± 1%. Intensities of transitions via other ^{14}C states are < 2% (1967TH05). [(1979GR1J; prelim.) find E_{γ} = 8173.92 ± 0.05 keV].
The coherent scattering length (thermal, bound) is 6.19 ± 0.09 fm, σ_{scatt} = 4.16 ± 0.13 b (1979KO26). 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 14.8 (in PDF or PS). High resolution σ_{t} measurements by (1979AU07) for E_{n} = 1.2 to 13.9 MeV are displayed in Fig. 6 of that paper but an analysis in terms of resonances has not been reported. See also (1978LA1H) and (1976GAYV).
For reaction (a) see (1973BI1B). For reaction (b) see (1970AJ04).
At E_{p} = 185 MeV (1973DA37) and 200 MeV (1979HO1F) the angular distributions of π^{+} and π^{} to the ground states of ^{14}C and ^{14}O are very different. The population of ^{14}C*(6.09, 8.32, 14.9 ± 0.2) is also reported (1973DA37). For crosssection measurements near threshold see (1979MA38, 1979MA39). See also (1976BO2C, 1979SOZY) and (1976NO1D; theor.).
Observed proton groups are displayed in Table 14.9 (in PDF or PS). Angular distributions have been measured at a number of energies up to E_{d} = 14.8 MeV [see (1976AJ04)] and at E_{dbar} = 13 MeV (1978DA17; to ^{14}C*(0, 6.09, 7.34)). For listings of θ^{2}_{n} see Table 14.5 (in PDF or PS) in (1970AJ04). Gamma rays are exhibited in Table 14.5 (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]. ^{14}C*(6.09) is 1^{} (decay is E1); ^{14}C*(6.59) is 0^{+} (internal pairs only); ^{14}C*(6.73) is 3^{} (γ_{0} is E3; l_{n} = 2); ^{14}C*(6.90) is 0^{} (no γ_{0}; 0.81 MeV cascade via 6.09 is predominantly dipole; γ_{0.8} + γ_{6.1} correlation is only consistent with J = 0, and plane polarization leads to negative parity); ^{14}C*(7.34) is 2^{} (strength of cascade decay and angular correlation results). See also (1974FI1D) and ^{15}N.
See (1976AJ04).
At E(^{7}Li) = 34 MeV the angular distribution has been measured for the ground state transition. ^{14}C*(6.09, 6.73) and possibly other states are also populated (1973SC26).
At E(^{11}B) = 114 MeV ^{14}C_{g.s.} is weakly excited but ^{14}C*(6.73, 7.34) [J^{π} = 3^{} and 2^{}] are strongly populated (1974AN36).
See (1979KOZZ).
See (1976GA37) and (1976AJ04). See also (1978OS06; theor.).
Angular distributions have been measured at E(^{17}O) = 29.8 and 32.3 MeV (1977CH22, 1978CH16) and E(^{18}O) = 31.0 MeV (1978CH16).
^{14}B decays primarily to ^{14}C*(6.09, 6.73): see Table 14.2 (in PDF or PS). The halflife is 16.1 ± 1.2 msec: see ^{14}B.
See (1976AJ04) and (1979KI11; theor.).
The charge radius of ^{14}C, r_{rms} = 2.56 ± 0.05 fm (1973KL12). At E_{e} = 37, 50 and 60 MeV (θ = 180°), inelastic groups are observed to ^{14}C*(7.01, 7.34, 8.32, 9.80, 10.5, 11.31 ± 0.02, 12.96, 14.67) with J^{π} = 2^{+}, 2^{}, 2^{+}, (1), , 1^{+} and (3, 4), respectively, for the states with 7.0 < E_{x} < 13.0 MeV. ^{14}C*(11.31) dominates the spectrum: this 1^{+} state has Γ = 207 ± 13 keV and Γ_{γ0} = 6.8 ± 1.4 eV (1977CR02). There is no evidence of sharp structure in the region E_{x} = 19 to 24 MeV where the T = 2 analog state of ^{14}B_{g.s.} would be expected (1974KL12: E_{e} = 61.5 and 80.7 MeV). See also (1976AJ04) and (1979KI11, 1980ER01; theor.).
For reaction (a) see (1976AJ04). Angular distributions have also been studied at E_{d} = 17 MeV to ^{14}C*(0, 6.73, 7.01) (1975CE04). See also (1976AJ04).
Elastic angular distributions have been measured at E(^{3}He) = 4.5, 5.1 and 5.8 MeV (1972KE08) and 10, 12, 15 and 18 MeV (1970DU07).
Elastic angular distributions have been studied at E_{α} = 22, 24 and 28 MeV (1972OE01, 1973OE01).
The elastic scattering for reaction (a) has been studied at E(^{12}C) = 12, 15, 18 and 20 MeV and for reaction (b) at 15 MeV (1972BO68). Yields of γrays from ^{14}C*(6.73) for E(^{14}C) = 40 to 57 MeV are reported by (1980FR03).
See (1976AJ04).
The elastic scattering angular distributions have been measured at E(^{16}O) = 20, 25 and 30 MeV (1975SC35). See also (1978BE2C) and (1979HE02; theor.).
Branching ratios have been measured for the capture of stopped pions to ^{14}C*(0, 7.0 ± 0.1, 8.3, 11.3, 20.0 ± 1.0) (1975BA52): the total radiative capture branching is 2.1 ± 0.2%. The preliminary results of (1979AL1M) are in general agreement, but it is suggested that the E_{x} of the fourth group is 10.7 MeV. See also (1977RI1H, 1979PE1C) and the "GENERAL" section here.
The p_{0} angular distribution has been measured at E_{n} = 14 MeV (1971CO32). See also ^{15}N, (1976KI1D, 1978NE1A, 1978NE1B), (1977CO1U: astrophys.) and (1976AJ04).
See (1970AJ04).
See (1976AJ04).
For E_{bs} = 19.6 to 38.3 MeV, ^{14}C*(0, 6.1 + 6.6 + 6.9, 7.0, 10.7) are preferentially excited (1972DE1D, 1976PA22). See also ^{15}N. For reaction (b) see (1975MU07).
Ground state angular distributions have been measured for E_{n} = 14.1  14.8 MeV: see (1976AJ04) and (1978BA1M). See also ^{16}N in (1982AJ01).
^{14}C states populated in this reaction are displayed in Table 14.9 (in PDF or PS) of (1976AJ04), together with l and C^{2}S values (1971KA35: E_{d} = 52 MeV).
See (1976AJ04).
At E_{π} = 230 MeV, γrays from the population of ^{14}C*(6.73, 6.90) are observed (1974LI15).
At E(^{6}Li) = 93 MeV ^{14}C*(0, 7.01, 8.32, 10.45) are populated, the first two of these strongly (1976WE09, 1977WE1B).
See (1976AJ04).
Angular distributions are reported at E(^{18}O) = 28 and 32 MeV (1971BA68) and 36.1 MeV (1977KA26).
See ^{18}O in (1978AJ03).
At E_{bs} = 23.5 and 28 MeV ^{14}C*(6.09, 6.73) are excited (1976BA41). See also ^{18}O in (1978AJ03).
See (1978BE1H) and (1976AJ04).
See (1976AJ04).
