
^{14}C (1976AJ04)(See Energy Level Diagrams for ^{14}C) 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 ^{14}C: (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 ^{14}C: 14.003241983 (12) amu (1975SM02).
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 ^{14}O(β^{+}) cannot be accounted for by the differences in the binding energies of ^{14}C and ^{14}O (1972WI05). For other discussions of the long lifetime of ^{14}C see (1959AJ76, 1970AJ04) and (1976GOZX). See also (1970SO08) and (1969EL1A, 1970FR13, 1971HU10, 1973HA49, 1973KU1J, 1974ZA1G; theor.).
^{†} (W. Mann, private communication.)
These reactions have been studied with E(^{7}Li) to 6.5 MeV: see (1970AJ04) for the earlier 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).
Observed proton groups are displayed in Table 14.4 (in PDF or PS) (1973AJ01). Angular distributions have been measured at E(^{6}Li) = 1.9 MeV (1969KO1A: p_{0}, p_{1}, p_{2+3+4+5}, p_{6}, p_{7}, p_{8}) and at 20 MeV ((1973AJ01) and unpublished results: to most states shown in Table 14.4 (in PDF or PS)). See also ^{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). Angular distributions for the d_{0} group have also been measured at E(^{7}Li) = 1.7 to 1.9 MeV (1969KA1C). The γdecay 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 ^{14}C*(7.01).
At E(^{13}C) = 9 MeV ^{14}C*(6.09, 6.73, 6.90) have been populated: τ_{m} < 10, > 5 × 10^{4} and 36 ± 4 fsec, respectively (1975SE04). See also (1975SE03).
The yield of 3.7 MeV γrays coincident with E_{β} > 4 MeV (from the ^{13}B 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 ^{14}B*(0.74) or (1.38) (1974GO1T).
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 ^{14}C in the range 21.54 < E_{x} < 22.42 MeV (1965VA13).
Angular distributions of p_{0} 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 ^{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  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 14.5 (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: p_{0}). Particlegamma correlations have been studied by (1968BE30): see Table 14.6 (in PDF or PS). The lifetime of ^{14}C*(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 ^{14}C*(6.73) 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 (1969AR1B), (1974BA65; theor.) and ^{15}N.
At E(^{12}C) = 114 MeV ^{14}C*(6.73, 10.25) [J^{π} = 3^{} and 4^{+}, respectively] are populated (1972SC21, 1974AN36). See also (1971SC1F, 1972MO1E, 1973SC1J).
For reaction (b) see (1970BA1J, 1974CH1Q). See also (1970AJ04), (1974GO1L) and (1970AN1D, 1971AL1D, 1971RO1G, 1972RO35, 1975TA02; theor.). For reaction (a) see (1975NA11).
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 ^{14}C*(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 ^{13}C is not significantly involved as a neutron poison in sprocess nucleosynthesis (1971AL09). See also (1970CL1C, 1973CL1E; astrophys. questions). 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).
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).
See (1973BI1B).
See (1970AJ04).
At E_{p} = 185 MeV, an angular distribution has been measured for the transition to ^{14}C_{g.s.}: it is forward peaked and goes through a minimum at 90° [while the π^{} to ^{14}O_{g.s.} show a flat distribution: see reaction 6 in ^{14}O]. There is evidence also for the population of ^{14}C*(6.09, 8.32, 14.9 ± 0.2) as well as some other structure (1973DA37). See also (1970DO04).
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 p_{0} 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 θ^{2}_{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]. ^{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 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, in particular, (1958WA02, 1965LA09, 1966AL10,, 1966RI02, 1966WA1C). τ_{m} < 15 fsec (1974RU1B), < 40 fsec (1973RE1E, 1973RE1F; prelim. results) for ^{14}C*(6.09). See also (1967SP09) and ^{15}N.
See (1961BA10).
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^{}, respectively] are strongly populated (1974AN36). See also (1972MO1E, 1973SC1J).
See (1971GA05) and (1973TO05; theor.) for reaction (a). For reaction (b) see ^{14}N, reaction 60 (1975GA17).
See (1974CH1Q).
^{14}B decays primarily to ^{14}C*(6.09, 6.73): see Table 14.2 (in PDF or PS). τ_{1/2} = 16.1 ± 1.2 msec (1974AL11).
See (1973KI05; theor.).
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, ^{14}C*(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 ^{14}C including ^{14}C*(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 ^{14}B_{g.s.} would be expected (1974KL12: E_{e} = 61.5 and 80.7 MeV). See also (1973FA1K, 1974DE1E).
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 ^{14}C*(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 ^{14}C*(0, 6.73, 7.01) (1975CE04).
The elastic angular distribution has been measured at E(^{3}He) = 10, 12, 15 and 18 MeV (1970DU07). See also (1971CO14).
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). See also (1973FE03), (1974GO1L) and (1973MC1J, 1973VO04, 1975DE09, 1975VO1B; theor.).
See (1971BO1U) and (1971VO1D, 1975DE09, 1975VO1B; theor.).
The elastic scattering angular distributions have been measured at E(^{16}O) = 20, 25 and 30 MeV (1974KO1P).
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%.
^{14}C*(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 ^{14}C*(6.73) (1971NY03). The p_{0} angular distribution has been measured at E_{n} = 14 MeV (1971CO32). See also (1970AJ04), (1970DI1A), (1973CL1E; astrophys. questions) and ^{15}N.
See (1970AJ04).
See (1971BAWQ).
For E_{bs} = 19.6 to 38.3 MeV ^{14}C 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 ^{15}N. For reaction (b) see (1975MU07).
The angular distributions of n_{0} have been measured at E_{n} = 14.1 and 14.8 MeV (1967FE06, 1971MI12).
^{14}C 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 lvalues obtained from the analysis of the angular distributions (1971KA35).
Angular distributions of the α_{0} group have been measured at E_{t} = 0.82 to 1.62 MeV (1973AB1E). See also ^{18}O in (1978AJ03).
At E_{π} = 230 MeV, γrays from the population of ^{14}C*(6.73, 6.90) are observed (1974LI15). See also (1971KO23).
See (1973CE1B).
See (1972KU1H; theor.).
Angular distributions are reported at E(^{18}O) = 28 and 32 MeV (1971BA68).
See ^{18}O in (1978AJ03) and (1973CL1E; astrophys. relevance).
See (1975BE01), (1970AJ04) and (1974DO03; theor.).
See (1967DE03).
Not observed: see (1962LA15).
