(See Energy Level Diagrams for 14C)
Applied work: (1985BA2G, 1985GO1R, 1986CI1B, 1986CS1B, 1986DO1M, 1986EF1A, 1986HO1L, 1986KI1J, 1986KO2A, 1986SR1B, 1986SU1H, 1987AR1N, 1987BA2M, 1987BA2N, 1987BO1U, 1987CU1E, 1987DU1G, 1987GA1E, 1987GO1W, 1987HE1F, 1987HE1G, 1987HO1J, 1987JA1G, 1987KI1I, 1987KO1T, 1987KR1O, 1987KU1C, 1987LO1E, 1987MA2E, 1987NA1N, 1987NA1O, 1987OE1A, 1987OS1F, 1987PO1K, 1987RE1H, 1987SE1D, 1987SL1A, 1987TA1K, 1987VA1S, 1988DO1D, 1988EL1C, 1988JU1B, 1988PU1A, 1988SU1E, 1989LO14, 1989MU1A, 1990DO1C, 1990SA1J).
Complex reactions involving 14C: (1985AL28, 1985BA2G, 1985BE40, 1985BR1F, 1985HO21, 1985KA1E, 1985KA1F, 1985KA1G, 1985KU24, 1985KW03, 1985PO12, 1985PO11, 1985PO14, 1985SI19, 1985VI01, 1986BA26, 1986BI1A, 1986CS1A, 1986DE32, 1986HA1B, 1986IR01, 1986ME06, 1986PA1N, 1986PI11, 1986PO06, 1986PO15, 1986PR1B, 1986SO10, 1986UT01, 1987BA38, 1987BL04, 1987BUZP, 1987BU07, 1987GU04, 1987HE1H, 1987IV01, 1987NA01, 1987PO1F, 1987PO1L, 1987PR1E, 1987RI03, 1987RU1C, 1987RU1D, 1987SH04, 1987SN01, 1987VI02, 1987YA16, 1988BA01, 1988BE56, 1988BL11, 1988CA06, 1988IV1C, 1988JO1B, 1988PR1B, 1988RU01, 1988SA19, 1988SA35, 1988SA1X, 1988SH29, 1989BA92, 1989BR34, 1989BU06, 1989BU05, 1989BU1H, 1989BU1I, 1989CI03, 1989CI1C, 1989FL1A, 1989GIZV, 1989GRZQ, 1989GU1B, 1989HO16, 1989KI13, 1989MA21, 1989MA43, 1989PO1I, 1989PO18, 1989PR02, 1989PR06, 1989PR1F, 1989SA1L, 1989SA10, 1989SA45, 1989SH37, 1989TE02, 1989YO02, 1990AR1E, 1990BU09, 1990BU13, 1990HU02, 1990OG01, 1990SH01, 1990WE01, 1990YA02).
Pion and kaon capture and reactions (See also reactions 15, 23, 31 and 32.): (1985AL15, 1985BA1A, 1985CH1G, 1985KO1Y, 1985TU1B, 1986BA1C, 1986BE1P, 1986BO1N, 1986CE04, 1986DY02, 1986ER1A, 1986FE1A, 1986FO06, 1986GE06, 1986GI06, 1986MA1C, 1986SI11, 1986SU18, 1986WU1D, 1987BA2F, 1987BL15, 1987DOZY, 1987GI1C, 1987JO1B, 1987KA39, 1987KO1Q, 1987MI02, 1987ROZY, 1988BA2D, 1988BA2R, 1988HA37, 1988KO1V, 1988LE1G, 1988MI1K, 1988OH04, 1988OS1A, 1988PA06, 1988RO1M, 1988TI06, 1988YU04, 1989CH31, 1989DI1B, 1989DO1K, 1989JO07, 1989LE11, 1989SI1B, 1989SI1D, 1990HAZV).
Q0 = 0.137(9) b.
The adopted value of the half-life is 5730 ± 40 y: see (1976AJ04). Using Qm, log ft = 9.04 (1971GO40). For discussions of the lifetime of 14C see (1959AJ76, 1970AJ04, 1976AJ04). See also (1988YA10, 1988WRZZ, 1989DO1B, 1989PO1K, 1989SA1P, 1989WO1E; theor.). For the internal bremsstrahlung spectrum see (1988RA37).
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. There is a report of several broad structures in the 0° yield of α0 and α1 for E(7Li) = 2 to 20 MeV: it is suggested that they are due to a forward-direction cluster transfer process: see (1976AJ04) for references. For other work see (1970AJ04, 1986AJ01). For reaction (a) see also (1987SC11).
Angular distributions have been measured at E(7Li) = 5.6 to 6.2 MeV for the deuterons to 14C*(0, 6.09, 6.59 + 6.73, 6.90 + 7.01, 7.34, 8.32). Gamma rays with Eγ = 6094.5 ± 3.2, 6728.1 ± 1.4 and 7011.7 ± 5.2 keV have been reported: see (1981AJ01) for references. For τm and Eγ measurements see Tables 14.4 (in PDF or PS) in (1986AJ01) and 14.4 (in PDF or PS) here (1981KO08) [see this reference for an extensive study of electromagnetic transitions in 14C and 14N].
Angular distributions of p0 have been measured at Eα = 1.43 to 31.2 MeV: see (1976AJ04, 1981AJ01, 1986AJ01). At Eα = 118.1 MeV angular distributions have been studied [DWBA analysis] to 14C*(6.09, 6.59, 6.73, 7.01, 8.32, 9.80, 10.43[u], 10.74, 11.38[u], 11.7[u], 14.67, 14.87, 15.20, 16.43, 16.72, 17.30, 21.40 [u?]). It is suggested that one of the states at 11.7 MeV has Jπ = 4- and the other Jπ = (1, 2, 3)-, and that the state at 16.43 has Jπ = 6- (1987AN04). At Eα = 48 MeV an angular distribution is reported to a state at Ex = 23.288 ± 0.015 MeV with Γlab = 70 ± 3 keV. The sharpness of the state suggests that J is large, and that perhaps it is a 7- state (1988BR26, and J.D. Brown, private communication). A search has been made for an 8- state up to 26 MeV (at 20°): the upper limit for its strength is 0.2 that for the 23.29 MeV state (J.D. Brown, private communication). See also 15N, (1989BR1J) and (1988CA26; astrophys.).
Below Ex = 10.4 MeV, 14C*(6.09, 6.73, 6.90 + 7.01, 7.34, 8.32, 9.78) are observed in both reactions at E(Li) = 34 MeV (1984CL08): the states observed at higher excitation energies are displayed in Table 14.6 (in PDF or PS). The intensities of the 3He and α groups in the two reactions are significantly different. Comparison of the angular distributions in reaction (a) and in the analog reaction 11B(6Li, t)14N, as well as other data, leads to the assignment of analog pairs: see reaction 11 in 14N. It is suggested that 14C*(11.73) and not 14C*(11.67) is populated in the inelastic pion scattering (1984CL08). For the earlier work on reaction (b), see (1976AJ04).
Observed proton groups are displayed in Table 14.7 (in PDF or PS). Angular distributions have been measured at Et = 5.5 to 23 MeV [see (1981AJ01)] and at 33 MeV (1986COZO; prelim.; to 14C*(6.09, 6.6[u], 7.01, 8.31, 10.5[u], 14.87, 16.43). For other results see (1986AJ01). See also 15N.
At Eα = 65 MeV angular distributions have been measured to 14C*(0, 6.73 ± 0.02, 8.40 ± 0.14, 10.69 ± 0.05, 11.69 ± 0.06[u], 14.84 ± 0.4). The two most strongly populated states (or groups of states) are 14C*(6.73, 10.69). Jπ = 1- and (6+, 5-) are favored for 14C*(11.69, 14.84). For the latter 4+ is considered to be very unlikely: see (1986AJ01). See also (1981AJ01) for the earlier work.
See 18O in (1987AJ02).
The thermal capture cross section is 1.37 ± 0.04 mb (1982MU14). The decay is primarily to 14C*(0, 6.59) [(84.0 ± 2.3)%, (8.5 ± 0.5)%, (8.5 ± 0.5)%] with weaker branches to 14C*(6.09, 6.90) [(2.5 ± 0.5)%, (4.9 ± 1)%]. Gamma rays with Eγ = 8173.92, 6092.4 ± 0.2, 2082.6 ± 0.3, 1586.8 ± 0.2, 1273.9 ± 0.2, 808.9 ± 0.2 and 495.4 ± 0.3 keV have been observed: Ex = 6093.8 ± 0.2, 6589.4 ± 0.2 and 6902.6 ± 0.2 keV are reported for 14C*(6.09, 6.59, 6.90). The neutron capture yield for En = 95 to 235 keV shows a resonance at En = 152 ± 1 keV, Γlab = 5 ± 1 keV: see Table 14.8 (in PDF or PS) in (1981AJ01). A revised value of Γγ is 2.4 ± 0.9 eV [see R.L. Macklin quoted in (1990RA03)]. A recent remeasurement of the on- and off-resonance capture determines the following Γγ (in meV) for the listed transitions: 8.32 → g.s. = 34+13-6; 8.32 → 6.09 = 151+76-33; 8.32 → 6.73 = 30+30-13. Thus the total radition width for 14C*(8.32) is 215+84-35 meV. The off-resonance capture cross section is 20 ± 9 μb (1990RA03). The decrease by an order of magnitude in the Γγ of 14C*(8.32) has an important bearing on nucleosynthesis and appears to significantly reduce the production of A ≥ 14 nuclei in the non-standard Big Bang (1990RA03).
Angular distributions of cross sections and Ay and the 90° γ0 cross sections have been measured in the range Epol. n = 5.6 to 17 MeV. M1 resonances are indicated at En ~ 9.2 and 10.1 MeV (Γ ~ 200 keV) [Ex = 16.7 and 17.5 MeV]. σ(E2) is less than 2% of the total capture cross section for En = 5.6 to 17 MeV (1985WR01). See also (1988MA1U, 1989DE28; astrophysics) and (1985WE06, 1986HO1N, 1987LY01, 1988HO06, 1988HO1E, 1988RA10; theor.).
The coherent scattering length (thermal, bound) is 6.19 ± 0.09 fm, σscatt = 4.16 ± 0.13 b (1979KO26) [see, however, (1986AJ01)]. aj=1 = 5.5 ± 0.1 fm; aj=0 = 6.6 ± 0.4 fm: see (1987LY01). The total cross section has been measured from 0.1 to 23 MeV: see (1988MCZT, 1981AJ01).
The cross section for reaction (b) has been studied for En = 7.5 to 14.8 MeV: see unpublished work quoted in (1987RE01). Double differential cross sections have been studied at 4.55 ≤ En ≤ 10.99 MeV: evidence is found for the excitation of 14C states [Ex = 15.8 - 18.4 MeV] which decay to 12Cg.s. via 13C*(7.55) [Jπ = 5/2-] (1987RE01).
At Ep = 185 and 200 MeV the angular distributions of π+ and π- to the ground states of 14C and 14O are very different: see (1986AJ01). Angular distributions and Ay measurements have been reported at Epol. p = 200 MeV by (1987KO01, 1989KO21) to 14C*(0, 6.09, 6.9[u], 7.34, 8.32, 9.8[u], 10.4[u], 10.7[u], 11.7[u], (13.0, 13.6), 14.87[u], 18.5 [broad], 23.2). The latter state has an energy of 23.2 ± 0.1 MeV and Γ < / ~ 85 keV: it is not clear whether this is the same state as that reported in the 11B(α, p)14C reaction at 23.29 MeV (Dr. S. Vigdor, private communication). Ay ~ 0 at all angles for this state (1987KO01, 1989KO21). Assuming that the π± groups to 14C*(6.9) and 14O*(6.3) correspond to single states, and that the first populates 14C*(6.73) [Jπ = 3-], then 14O*(6.27) is assigned Jπ = 3- also. A similar comparison of 14C*(14.87) with 14O*(14.15), and with 14N*(16.91) [Jπ = 5-; 1] suggests Jπ = 5- for these 14C and 14O states (1989KO21). (1988HU04) report differential cross sections at Ep = 250, 354 and 489 MeV to 14C*(0, 6.09, 6.7[u], 7.34, 8.32, 9.80[u], 10.5[u], 11.7[u], 14.87, 23.2) and to previously unreported states at Ex = 13.50 and 14.05 MeV: The (p, π+) reactions show an enhancement of the σ(θ) near the invariant mass of the δ1232, in contrast with the (p, π-) reactions. A broad structure near Ex = 25 MeV is also observed (1988HU06) [see also for a continuum study]. (R.D. Bent and G.M. Huber, private communication) report that, from their measurements, Ex = 23.2 ± 0.6 MeV and Γc.m. < 200 keV. The assignment of Jπ = 5- to 14N*(14.87) [see Fig. 2 of (1988HU04)] is tentative. The uncertainties in the Ex = 13.50 and 14.05 MeV states are ± 100 keV and their Γc.m. are < 200 keV. I am greatly indebted to Drs. Bent and Huber for their comments. See also reaction 5 in 14O, (1986JA1H, 1988HU11) and (1987KU06; theor.).
Observed proton groups are displayed in Table 14.10 (in PDF or PS) of (1986AJ01). Recent measurements of proton groups, using a spectrograph, give Ex = 6094.05 ± 0.11, 6589.58 ± 0.39, 6731.58 ± 0.11, 6902.24 ± 0.18, 7011.4 ± 0.8 and 7342.65 ± 0.32 keV (1990PI05). Angular distributions have been measured at a number of deuteron energies up to 17.7 MeV: see (1981AJ01, 1986AJ01).
Gamma rays are exhibited in Table 14.4 (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 a listing 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 only consistent with J = 0, and plane polarization leads to negative parity); 14C*(7.34) is 2- (strength of cascade decay and angular correlation results). For a study of the pair decay of 14C*(6.90) [Jπ = 0-] see (1986PA23). See also 15N, (1987AB04) and (1985ME1E; applied).
In reaction (b) at Et = 38 MeV angular distributions have been studied to 14C*(0, 6.09, 6.6[u], 7.0[u], 7.34, 8.32, 9.8, 10.4[u]) (1988SI08).
The cross sections for reactions (a) and (b) have been measured with monochromatic photons to Eγ = 36 MeV (and the (γ, Tn) cross section has been derived) by (1985PY01). A sharp state is observed [with σ ~ 3 mb] at Ex = 11.25 ± 0.05 MeV (1985PY01) [also observed in the (γ, n0) work of (1985KU01) and showing a pronounced E1-M1 interference], sitting on a 1 mb tail of the GDR. The integrated value of the cross section is 1.1 ± 0.1 MeV · mb, yielding Γγ0 = 12 ± 1 eV. Most of the M1 strength of the 12C core is concentrated at 11.3 MeV (1985PY01). While other states on 14C affect the (γ, n) cross section at higher energies there is no evidence of pigmy resonances. The next major peak is at 15.5 MeV (σ ~ 9.1 mb), whose decay is by neutrons to 12Cg.s.. Above 17.5 MeV the neutron decay becomes more complex (1985PY01). Reaction (b) has little strength below 23.3 MeV. Above that energy, states of 14C (T>) can decay to 13C*(15.1) [T = 3/2], which subsequently decays by neutron emission (1985PY01). See also the (γ, n0) work of (1985KU01), (1988DI02) and (1985GO1A, 1987GO09, 1987KI1C; theor.).
The charge radius of 14C, rr.m.s. = 2.56 ± 0.05 fm (1973KL12). At Ee = 37 - 60 MeV (θ = 180°) inelastic groups are reported to 14C*(7.01, 7.34, 8.32, 9.80, 10.5, 11.31 ± 0.02, 12.96, 14.67) with the 11.3 MeV state [1+, Γ = 207 ± 13 keV, Γγ0 = 6.8 ± 1.4 eV] dominant (1977CR02). At Ee = 81.9 to 268.9 MeV (θ = 180°) (1989PL05, 1984PL02) find the dominant strength to be to 4 states at 11.7, 17.3 and 24.4 MeV [± 0.1 MeV]. The first two of these are T = 1 states reported in the (π, π) reaction below, the third is suggested to have T = 2 (and to be unresolved from a 2- state). The M4 form factors account for 41% and 37% of the T = 1 and T = 2 single-particle (e, e') cross section, respectively. The observed transitions to the T = 1 states exhaust 33 - 45% of the total isovector transition strength and 1 - 15% of the isoscalar transition strength. Magnetic electron scattering is most sensitive to isovector transitions (1984PL02). The population of 14C*(6.1, 6.7, 7.0, 8.3, 9.84 ± 0.05, 10.50 ± 0.05, 12.2 ± 0.1, 12.9 ± 0.1, 13.6 ± 0.1, 14.0 ± 0.1, 14.9 ± 0.1, 15.2 ± 0.1, 16.5 ± 0.1, 22.1 ± 0.1) is also reported (1989PL05, 1984PL02). See also (1987DE43, 1986HI06, 1989AJ1A) and (1986LI1C, 1987GO08, 1987KI1C, 1987LI30, 1988CL03, 1988HO1E, 1990CL02, 1990GA1M; theor.).
Elastic angular distributions have been measured at Eπ± = 50 MeV (1985MI16), 65 and 80 MeV (1983BL11) and 164 MeV (1986HA2E). At Eπ± = 164 MeV, the differential cross sections for the transition to 14C*(7.01) [Jπ = 2+1] are nearly the same for π+ and π-. Angular distributions have also been studied to the 2+2 state, 14C*(8.32), and to an unresolved group at Ex = 10.4 MeV [the latter results are consistent with Jπ = 3- distribution] (1988HA14) [see for discussion of B(E2)]. In earlier work at Eπ± = 164 MeV angular distributions had been obtained to states at Ex = 6.7, 11.7, 15.2, 17.3 MeV [± 0.1 MeV] with Jπ = 3-, 4-, 4-, 4-. In addition a broad structure (Γ ~ 1.7 MeV) had been observed near 24.5 MeV. It may include a narrower peak at 24.4 MeV (1985HO07): see also the Erratum (1990HO1C). The population of 14C*(6.1, 12.6) has also been reported: see (1986AJ01). See also (1989AJ1A).
At Ep = 497 MeV 14C*(11.7, 17.3) [Jπ = 4-] are populated (1989CRZX; prelim.). Elastic angular distributions are reported at Ep = 35 and 40.1 MeV (1990YA01). See also (1981AJ01, 1986AJ01) [the work quoted in (1986AJ01) has not been published.]
Elastic angular distributions have been studied at E(3He) = 4.5 to 18 MeV [see (1976AJ04)], at 22 MeV (1988AD1B; prelim.) and 72 MeV (1988DE34, 1989ER05) and at 39.6 MeV (1987BUZR; prelim.). See also (1989DE1Q, 1989GA1I) and (1986ZE04; theor.).
Elastic angular distributions have been studied at Eα = 22, 24 and 28 MeV [see (1976AJ04)] and at Eα = 35.5 MeV (1984PE24). At the latter energy many inelastic groups have also been studied: see Table 14.9 (in PDF or PS) (1984PE24). See also 18O in (1987AJ02) and (1985UM01; theor.).
The elastic scattering for reaction (a) has been studied at E(14C) = 20 to 40.3 MeV (1986STZY; prelim.) and 31 to 56 MeV (1985KO04); that for reaction (b) has been studied at E(13C) = 20 to 27.5 MeV (1988BI11) [see also reaction 50 in 13C]; and that for reaction (c) is reported at E(14C) = 31 to 56 MeV: see (1986AJ01). For the earlier work see (1976AJ04). For yield and fusion studies see (1986AJ01) and (1986STZY). The yields of γ-rays from 14C*(6.73) [Jπ = 3-] have been measured for E(14C) = 25 to 70 MeV: see (1986AJ01). See also (1990VO1E) and (1986BA69; theor.).
See (1986BA69; theor.).
The elastic scattering has been studied in reaction (a) at E(16O) = 20, 25 and 30 MeV [see (1981AJ01)] and at E(14C) = 20 to 43 MeV (1986STZY; prelim.); that for reaction (c) has been studied for E(14C) = 20 to 30 MeV (1986STZY). The α-breakup in reaction (c) is being investigated at E(18O) = 33.5 to 64 MeV (1988AL1F; prelim.). For excitation functions see (1986AJ04) and (1986STZY). See also (1989CI1C) and (1986BA69; theor.).
Differential cross sections to 14Cg.s. have been measured at Eγ = 173 MeV (1985RO05, 1987RO23), at 200 MeV (1985CO15), at 230, 260 MeV and 320 MeV (1986TE01, 1990GH01) and at 320 and 400 MeV (1990DI1D; prelim.). The transitions to the 2+ states at 7.01 + 8.32[u] and 10.7 MeV have been studied by (1987SU17) [see for B(M1)]. See also (1985BE1K, 1987HU01, 1987YA1J), (1986WI10, 1988TI06, 1990ER03; theor.) and the "GENERAL" section.
The photon spectrum from stopped pions is dominated by peaks corresponding to 14C*(6.7 + 6.9 + 7.0[u], 8.32, 10.7) and branching ratios have been obtained for these and the g.s. transition. That to 14C*(6.7 + 6.9 + 7.0) is (6.22 ± 0.40)% (absolute branching ratio per stopped pion) (1986PE05). For the earlier work see (1981AJ01). See also the "GENERAL" section.
The p0 angular distribution has been measured at En = 14 MeV: see (1981AJ01). At En = 60 MeV the strongest transitions are to 14C*(7.0 + 8.3, 11.3, 15.4) and to the giant resonanace peak, centered at ~ 20.4 MeV, and angular distributions have been studied to these groups: see (1986AJ01). For cross sections of astrophysical interest see 15N. A study of P-odd and left-right asymmetries with polarized thermal neutrons is reported by (1988AN19). See also (1986BO1K, 1988EL1C; applied).
At Et = 33.4 MeV 14C*(0, 6.09, 6.73, 7.34, 8.32) are populated (1988CL04).
See (1986GO1B; prelim.; E(14N) = 150 MeV).
At E(6Li) = 93 MeV 14C*(0, 7.01, 8.32, 10.45) are populated, the first two of these strongly: see (1981AJ01).