(See the Energy Level Diagram for 11C)
GENERAL: See also Table 11.8 [Table of Energy Levels] (in PDF or PS).
Theory: See (1956KU1A, 1957KU58, 1958FR1C).
The spectrum is simple; Eβ+(max) = 968 ± 8 keV (1954WO23). The mean of half-lives reported in (1955AJ61) is 20.36 ± 0.05 min. Recent values of the half-lives 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 K-capture to positron emission is 0.19 ± 0.03 % (1957SC29). See also (1957BR18, 1957KA1C).
See (1952PO27, 1953KU08, 1954MO1E).
For Ep = 0.7 to 3 MeV, the main capture radiation is to the ground state. Weaker radiations, ≈ 5%, with Eγ ≈ 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 + 0.5cos2θ. Using σα = 16 mb/sr, (1956CH20) find ωΓp ≈ 40 keV, Γα ≈ 500 keV, ωΓγ = 10 eV, consistent with M1 radiation. The angular distribution and the gamma-ray width appear to rule out all J ≤ 7/2 except J = 5/2- (1956CH20); see, however, 10B(p, α)7Be (1956CR07). The cross section increases rapidly in the range Ep = 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 Ep = 5.35 MeV, ≤ 2 mb at Ep = 5.51 MeV (1959GI47). See (1958MA1F, 1958TA03) and 10C.
The elastic scattering cross section at θ = 138° rises from nearly the Rutherford value for Ep < 0.9 MeV to 4 times Rutherford at Ep = 1.6 MeV. Anomalies are observed at Ep = 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 10B, rises monotonically from Ep = 1.5 to 2.7 MeV (1952DA05, 1954DA20, 1957HU79). At Ep = 2.7 MeV the cross section is 11 ± 5 mb (1957HU79). Above Ep = 2.4 MeV, weak (≈ 1%) γ-rays of 1.00 ± 0.04 MeV (1.74 → 0.71 transition in 10B) and 2.12 ± 0.06 MeV (2.14 → g.s. transition) are observed (1957HU79). See also (1952CR30), (1956CH20) and (1957JA37).
The excitation function is a smooth exponential from Ep = 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 11C levels at 12.3, 13.8 ± 0.2 and 15.7 ± 0.2 MeV. The ground state α-particles (α0) exhibit broad resonances at Ep = 1.17 and 1.53 MeV superposed on a continuous isotropic background (1951BR10, 1956AL23, 1956CR07). Alpha particles to the 0.43 MeV 7Be state (α1) and 0.43 MeV γ-rays show only the resonance at Ep = 1.53 MeV (1951BR10, 1954DA20, 1956CH20, 1956CR07, 1957HU79). A summary of the evidence on the (10B + p) resonances is given in Tables 11.9 (in PDF or PS) and 11.10 (in PDF or PS).
The reaction cross section for α0 at the Ep = 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 α1 suggests 3/2-, 5/2+ as most likely; 3/2- would agree with the mirror level in 11B (1956CR07: see Table 11.10 (in PDF or PS)).
At the Ep = 1.5 MeV resonance, the angular distribution of α0 has the form 1 - 0.53cos2θ. Between resonances, coefficient of odd order Legendre polynomials show a sharp peak, indicating that the two levels have opposite parity. The α1 distribution at Ep = 1.5 MeV also shows interference effects. From the reaction cross section at Ep = 1.5 MeV, J ≥ 5/2. The most satisfactory account of the α0 and α1 angular distributions is given with the assumption of J = 7/2+, formed by s- and d-waves. 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 Ep = 1.2 MeV the (non-resonant) 430 keV γ-rays 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 Ex = 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: Ed = 1.5 MeV, θ = 60°).
Neutron threshold measurements indicate levels in 11C at 8.108, 8.431, and 8.661 MeV (1955MA76: ± 0.008 MeV). Gamma-ray measurements indicate lines with Eγ = 4.75 ± 0.03 MeV (1955SA1B), 5.35 ± 0.05 MeV (1955SA1B: from 11C*(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 11C*(6.50). In coincidence with neutrons to 11C*(4.26 and 4.75, unresolved) are Eγ = 4.28, ≈ 2.3, ≈ 2.0 MeV (1958MC1E). See also (1957BI78).
At E(3He) = 2 MeV, deuterons have been observed in coincidence with a 2.0 ± 0.1 MeV γ-ray (1957GO1B).
At Ep = 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 ground-state group is ≈ 2.5 times that of the 11C*(2.0) group at the four angles studied; I(0°)/I(20°) ≈ 2.5 for both groups. An appreciable number of low-energy (< 1.5 MeV) neutrons of undetermined origin is reported (1956AJ22). See also (1955MA84, 1958GO77).
See (1952BR52, 1956GR1E, 1956WE1B).
At E(3He) = 1.3 and 2.0 MeV, no 1.9 MeV γ-radiation (from 11C*(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).