
^{14}C (1959AJ76)(See the Energy Level Diagram for ^{14}C) GENERAL: See also Table 14.1 [Table of Energy Levels] (in PDF or PS). Theory: See (1954JA1A, 1955SH84, 1956EL1B, 1956GO1P, 1956ST1D, 1957CA1F, 1957GO1G, 1957SH1B, 1957VI1A, 1958BA1A, 1958SU1C).
The mean of reported end points is 156 ± 1 keV (1957LI51). The weighted mean halflife is 5568 ± 30 years (1955LI1D: see (1958ST50)): log ft = 9.03. The spectrum does not deviate from the allowed shape down to 3 keV (1954MO84); see also (1954FO29, 1955PO04). It appears that the long lifetime of ^{14}C may be due to chance cancellation in the matrix element for the decay, brought about by a small tensor force (1954JA1A, 1955SH84, 1956ST1D, 1957VI1A); see, however, (1958BA1A). See also (1955SM1A, 1957ST1G).
These reactions have been studied for E(^{7}Li) ≈ 1.3 to 2.0 MeV: see (1957NO14, 1957NO17).
At E(^{6}Li) = 2 MeV, the ground state proton group, and proton groups corresponding to the known levels between E_{x} = 6.1 and 8.5 MeV have been observed (1958LI42).
See (1951FR1B, 1953MA42) and ^{15}N.
See (1951PO1A, 1955CU17, 1956BA1E, 1956JA31, 1956MA09).
The thermal capture cross section is 0.5 ± 0.2 mb, 0.9 ± 0.3 mb (1955HU1B).
The thermal scattering cross section is 4.7 ± 0.09 b (1955HU1B: free atoms); see also (1952KO1A). In the range E_{n} = 0.2 to 3 MeV, resonances are observed at E_{n} = 1.75 MeV (Γ = 25 keV), 2.43 and 2.45 MeV. The latter levels, whose widths are of the order of 15 keV, interfere strongly. The nonresonant cross section decreases smoothly from about 3 b at 0.2 MeV to 1 b at 3 MeV (1958WI01).
See (1954SA68) and (1947HU03).
The weighted mean of seven Qvalues is 5.943 ± 0.003 MeV (1957VA11: see also (1954AH47, 1954SP01)). Proton groups reported by (1954SP01) and (1955MC75) are displayed in Table 14.2 (in PDF or PS). No other groups have been observed for E_{x} = 0 to 8.1 MeV with an intensity greater than 0.2 of the group corresponding to the 6.1 MeV state (1954SP01: θ = 90°). See also (1953KO42, 1956EL1A, 1956KO26, 1956VA17). Observed γradiation assigned to ^{14}C is exhibited in Table 14.3 (in PDF or PS). The internallyformed positron distribution suggests that the 6.1 MeV line is E1 and hence that the level has J = 1^{} and is the analog to the 8.06 MeV level of ^{14}N (1952TH24, 1958CH1A, 1958GO81). The 0.81 MeV cascade transition from the 6.89 MeV state shows a Doppler shift (τ_{m} < 3 × 10^{13} sec) 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 transition for the 6.89 MeV level (1958WA02). The 6.89 MeV level is probably the analog of the J = 0^{} level of ^{14}N at 8.71 MeV. Assuming that the 6.1 MeV radiation is E1, the relative intensities of external and internal pairs for the 6.1 and 6.7 MeV γrays are consistent with E2, E1, M1 or E3 for the 6.7 MeV transition (1955BE1G). The mean lifetime of the 6.72 MeV state is greater than 3 × 10^{13} sec, suggesting E3 or M2 (1958WA02). The 0.61 MeV γray is in coincidence with the 6.7 MeV γray and has an intensity roughly equal to that of the 7.35 MeV γray (within a factor of 5). The strength of the cascade then suggests J = 2^{} or 3^{} for the 7.35 MeV state (1958WA02): see also (1955AU1A; theor.). Comparison of reduced widths and calculation of level shifts suggests the following associations of ^{14}C and ^{14}N levels: 6.09  8.06, 6.72  8.91, 6.89  8.71 and 7.35  9.50 (1959WA04).
Not observed.
Not observed.
Reduced widths derived from pickup angular distributions at E_{d} = 14.8 MeV are listed in Table 14.4 (in PDF or PS) (1958MO97). The observation of strong contributions from ^{13}C excited states indicates considerable configuration mixing in the ground state of ^{14}C. An admixture of 2s^{2} and 2d^{2} consistent with these results also permits a satisfactory account of the cancellation in the ^{14}C^{14}N beta decay matrix element without recourse to tensor forces (1958BA1A). See also ^{14}C(β^{})^{14}N.
The weighted mean of five Qvalue determinations is 0.626 ± 0.001 MeV (1957VA11). See also (1951ST1D, 1952LI24, 1958DO63) and ^{15}N.
Not observed.
See ^{15}N.
See (1956FR1A).
Not observed.
See ^{18}O.
