(See Energy Level Diagrams for 14C)
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).
Mass of 14C: 14.003241983 (12) amu (1975SM02).
Measured τ1/2 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 τ1/2 = 5730 ± 40 y †. Using Qm, 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.)
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).
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have been measured at E(6Li) = 1.9 MeV (1969KO1A: p0, p1, p2+3+4+5, p6, p7, p8) and at 20 MeV ((1973AJ01) and unpublished results: to most states shown in Table 14.4 (in PDF or PS)).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.
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 Eγ = 6094.5 ± 3.2, 6728.1 ± 1.4 and 7011.7 ± 5.2 keV for the ground state transitions of these states and τm < 120 fsec for 14C*(7.01).
The yield of 3.7 MeV γ-rays coincident with Eβ > 4 MeV (from the 13B decay) has been measured for Eα = 13.6 to 17 MeV: a strong interference anomaly is observed which appears to correspond to Ex = 23.624 ± 0.036 MeV, Γc.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).
Resonant structure has been reported in the yield of neutrons with Et = 1.20 to 2.32 MeV: these are thought to correspond to ten excited states in 14C in the range 21.54 < Ex < 22.42 MeV (1965VA13).
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 - 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).
Observed proton groups are displayed in Table 14.5 (in PDF or PS). Angular distributions have been measured at Et = 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-31/2d5/2) configuration (1974AL07).
The thermal capture cross section is 0.9 ± 0.2 mb (1973MU14). The neutron capture yield has been measured for En = 95 to 235 keV. The parameters for 14C*(8.32) are En = 152 ± 1 keV, Γn = 5 ± 1 keV, Γγ = 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 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).
The coherent scattering length (thermal, bound) is 6.0 ± 0.2 fm (1973MU14). The total cross section has been measured for En = 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).
At Ep = 185 MeV, an angular distribution has been measured for the transition to 14Cg.s.: it is forward peaked and goes through a minimum at 90° [while the π- to 14Og.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).
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 Ed = 14.8 MeV: recent measurements have been carried out for the p0 group at Ep = 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 θ2n 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 Jπ 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; ln = 2); 14C*(6.90) is 0- (no γ0; 0.81 MeV cascade via 6.09 is predominantly dipole; γ0.8 + γ6.1 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). τm < 15 fsec (1974RU1B), < 40 fsec (1973RE1E, 1973RE1F; prelim. results) for 14C*(6.09). See also (1967SP09) and 15N.
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).
See (1973KI05; theor.).
The elastic scattering has been studied at Ee = 374.6 MeV: the charge radius rrms = 2.56 ± 0.05 fm (1973KL12). At Ee = 101.2 MeV, 14C*(7.01, 8.32) [both Jπ = 2+] are excited strongly: Γγ = 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 Ex = 19 to 24 MeV where the T = 2 analog state of 14Bg.s. would be expected (1974KL12: Ee = 61.5 and 80.7 MeV). See also (1973FA1K, 1974DE1E).
The elastic angular distribution has been measured by (1971CU01) at Ep = 14.5 MeV (reaction (a)) and by (1967NE06) at Ed = 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 Ed = 14.9 MeV. Angular distributions have also been studied at Ed = 17 MeV to 14C*(0, 6.73, 7.01) (1975CE04).
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.).
The elastic scattering angular distributions have been measured at E(16O) = 20, 25 and 30 MeV (1974KO1P).
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%.
14C*(6.09) decays with Eγ = 6098 ± 5 keV, τm < 0.1 psec (1972NY02), and Eγ = 6732 ± 5 keV from the decay of 14C*(6.73) (1971NY03). The p0 angular distribution has been measured at En = 14 MeV (1971CO32). See also (1970AJ04), (1970DI1A), (1973CL1E; astrophys. questions) and 15N.
For Ebs = 19.6 to 38.3 MeV 14C is reported to be formed preferentially in the ground state and in excited states with Ex = 7.0 ± 0.2 and 10.7 MeV (1971DE42). See also (1973DE30) and 15N. For reaction (b) see (1975MU07).
See (1972KU1H; theor.).
Angular distributions are reported at E(18O) = 28 and 32 MeV (1971BA68).
Not observed: see (1962LA15).