
^{11}C (1959AJ76)(See the Energy Level Diagram for ^{11}C) GENERAL: See also Table 11.8 [Table of Energy Levels] (in PDF or PS). Theory: See (1956KU1A, 1957KU58, 1958FR1C).
The spectrum is simple; E_{β+}(max) = 968 ± 8 keV (1954WO23). The mean of halflives reported in (1955AJ61) is 20.36 ± 0.05 min. Recent values of the halflives are 20.26 ± 0.1 min (1955BA63), 20.8 ± 0.2 min (1957PR53) and 20.11 ± 0.13 min (1958AR15); log ft = 3.62 (1954WO23). The ratio of Kcapture to positron emission is 0.19 ± 0.03 % (1957SC29). See also (1957BR18, 1957KA1C).
See (1957NO17).
See (1952PO27, 1953KU08, 1954MO1E).
For E_{p} = 0.7 to 3 MeV, the main capture radiation is to the ground state. Weaker radiations, ≈ 5%, with E_{γ} ≈ 4.2 and 5.8 MeV suggest a cascade through the 4.23 MeV level (1956CH20, 1957HU79). Two broad resonances are reported at 1.14 and ≈ 4.4 MeV: see Table 11.9 (in PDF or PS) (1954DA20, 1955BA22, 1955HA01, 1956CH20, 1957HU79). The angular distribution at the first resonance is 1 + 0.5cos^{2}θ. Using σ_{α} = 16 mb/sr, (1956CH20) find ωΓ_{p} ≈ 40 keV, Γ_{α} ≈ 500 keV, ωΓ_{γ} = 10 eV, consistent with M1 radiation. The angular distribution and the gammaray width appear to rule out all J ≤ 7/2 except J = 5/2^{} (1956CH20); see, however, ^{10}B(p, α)^{7}Be (1956CR07). The cross section increases rapidly in the range E_{p} = 2.2 to 2.7 MeV, but there is no indication of a previously reported 2.4 MeV resonance (see (1954DA20, 1955BA22, 1957HU79)). See also (1955AJ61, 1955WI1E) and (1957JA37).
The cross section is ≤ 1.4 mb at E_{p} = 5.35 MeV, ≤ 2 mb at E_{p} = 5.51 MeV (1959GI47). See (1958MA1F, 1958TA03) and ^{10}C.
The elastic scattering cross section at θ = 138° rises from nearly the Rutherford value for E_{p} < 0.9 MeV to 4 times Rutherford at E_{p} = 1.6 MeV. Anomalies are observed at E_{p} = 1.15 and 1.5 MeV (1951BR10). See Table 11.9 (in PDF or PS).
The yield of 0.71 MeV radiation, from the first excited state of ^{10}B, rises monotonically from E_{p} = 1.5 to 2.7 MeV (1952DA05, 1954DA20, 1957HU79). At E_{p} = 2.7 MeV the cross section is 11 ± 5 mb (1957HU79). Above E_{p} = 2.4 MeV, weak (≈ 1%) γrays of 1.00 ± 0.04 MeV (1.74 → 0.71 transition in ^{10}B) and 2.12 ± 0.06 MeV (2.14 → g.s. transition) are observed (1957HU79). See also (1952CR30), (1956CH20) and (1957JA37).
See ^{9}B.
See ^{8}Be.
The excitation function is a smooth exponential from E_{p} = 60 to 200 keV (1955BA1M). Excitation functions have been studied up to 3 MeV (see (1957JA37)). Using the stacked foil method, (1957KA1C) report structure in the excitation function corresponding to ^{11}C levels at 12.3, 13.8 ± 0.2 and 15.7 ± 0.2 MeV. The ground state αparticles (α_{0}) exhibit broad resonances at E_{p} = 1.17 and 1.53 MeV superposed on a continuous isotropic background (1951BR10, 1956AL23, 1956CR07). Alpha particles to the 0.43 MeV ^{7}Be state (α_{1}) and 0.43 MeV γrays show only the resonance at E_{p} = 1.53 MeV (1951BR10, 1954DA20, 1956CH20, 1956CR07, 1957HU79). A summary of the evidence on the (^{10}B + p) resonances is given in Tables 11.9 (in PDF or PS) and 11.10 (in PDF or PS). The reaction cross section for α_{0} at the E_{p} = 1.17 MeV resonance requires J ≥ 3/2. The angular distribution is isotropic, except for small terms attributed to interference, restricting the choice to 5/2^{+}, 7/2^{+}, 3/2^{}. The absence of α_{1} suggests 3/2^{}, 5/2^{+} as most likely; 3/2^{} would agree with the mirror level in ^{11}B (1956CR07: see Table 11.10 (in PDF or PS)). At the E_{p} = 1.5 MeV resonance, the angular distribution of α_{0} has the form 1  0.53cos^{2}θ. Between resonances, coefficient of odd order Legendre polynomials show a sharp peak, indicating that the two levels have opposite parity. The α_{1} distribution at E_{p} = 1.5 MeV also shows interference effects. From the reaction cross section at E_{p} = 1.5 MeV, J ≥ 5/2. The most satisfactory account of the α_{0} and α_{1} angular distributions is given with the assumption of J = 7/2^{+}, formed by s and dwaves. The assumption J = 5/2^{+}, 5/2^{} for the 1.17 and 1.5 MeV resonances is excluded (1956CR07: see Table 11.10 (in PDF or PS)). At E_{p} = 1.2 MeV the (nonresonant) 430 keV γrays are isotropic ± 2% (1956CH20). See also (1955WI1E).
Level information derived from studies of the neutron groups is displayed in Table 11.11 (in PDF or PS) (1952JO10, 1954PA29, 1956CE1B, 1956CE73, 1956GR54, 1956MA83, 1957GR50, 1958MC1E, 1959NE1A). See also (1953GI05, 1954BU06, 1956BO1F). A search for possible doublet structure at E_{x} = 6.50 MeV revealed no other level in this neighborhood. A group with relative intensity 1/10 would have been seen if the separation were as much as 40 keV (1959NE1A: E_{d} = 1.5 MeV, θ = 60°). Neutron threshold measurements indicate levels in ^{11}C at 8.108, 8.431, and 8.661 MeV (1955MA76: ± 0.008 MeV). Gammaray measurements indicate lines with E_{γ} = 4.75 ± 0.03 MeV (1955SA1B), 5.35 ± 0.05 MeV (1955SA1B: from ^{11}C*(7.4 → 2.0)), and 6.50 ± 0.03 (1955BE81: Doppler corrected), 6.52 ± 0.05 MeV (1955SA1B). Gamma rays of energy 6.5, 4.3, and ≈ 2.0 MeV are observed in coincidence with neutrons leading to ^{11}C*(6.50). In coincidence with neutrons to ^{11}C*(4.26 and 4.75, unresolved) are E_{γ} = 4.28, ≈ 2.3, ≈ 2.0 MeV (1958MC1E). See also (1957BI78).
At E(^{3}He) = 2 MeV, deuterons have been observed in coincidence with a 2.0 ± 0.1 MeV γray (1957GO1B).
Not reported.
See (1957NO17).
At E_{p} = 7.03 MeV, groups are observed corresponding to the ground state and to a state at 2.01 ± 0.06 MeV. The intensity of the groundstate group is ≈ 2.5 times that of the ^{11}C*(2.0) group at the four angles studied; I(0°)/I(20°) ≈ 2.5 for both groups. An appreciable number of lowenergy (< 1.5 MeV) neutrons of undetermined origin is reported (1956AJ22). See also (1955MA84, 1958GO77).
Not reported.
See ^{13}C.
See ^{12}C.
See (1952BR52, 1956GR1E, 1956WE1B).
At E(^{3}He) = 1.3 and 2.0 MeV, no 1.9 MeV γradiation (from ^{11}C*(2.0)) is observed by (1957BR18). The energy of the first excited state is 1.990 ± 0.010 MeV (1959PO61). See also (1952FR1A, 1952PO27, 1953KU08, 1958WE1E).
Not reported.
See ^{15}O.
See (1955AJ61).
