(See Energy Level Diagrams for 11C)
J = 3/2 (1961SN01).
The mean value of reported half-lives is 20.34 ± 0.04 min (see Table 11.15 (in PDF or PS)); ft = 3882. The ratio of K-capture of positron emission is (0.19 ± 0.03)% (1957SC29), (0.230+0.014-0.011)% (1967CA09). See also (1965GA1D, 1966MI1F, 1967AM1H).
At E(6Li) = 4.1 MeV, neutron groups have been observed to the first seven excited states and to the 8.42 MeV state. Associated γ-rays were used for the stop triggering of the time-of-flight system. The group to the 8.4 MeV state had an intensity ≈ 10% of that to the highest bound state at Ex = 7.5 MeV suggesting a small Γα for the 8.42 MeV state (compare 12C(3He, α)11C). No evidence for the γ-decay of the 8.11 MeV state was found (1966BA2U). See also (1957NO17, 1960NO1A, 1962BE16, 1962BE24).
Reported neutron groups are listed in Table 11.16 (in PDF or PS)). Angular distributions and excitation functions have been studied in the range E(3He) = 1.3 to 10 MeV by (1961DU1B, 1963DU12, 1963VA16, 1965DI06, 1965TO06, 1966AD1D: see (1966WE1B, 1968OK1D)). In the middle range of these energies, the reaction is dominated by direct interaction, but it is not clear whether two-particle stripping or knock-on processes are involved. Large back angle cross sections are unexplained by DWBA (1965TO06). At 10 MeV, the distributions are consistent with a predominant role for the two-nucleon stripping process. The contribution of the knock-on process appears to be small (1968OK1D).
Gamma branching ratios and multipolarities for 11C levels up to Ex = 7.5 MeV have been studied by (1965OL03, 1965RO07): see Table 11.17 (in PDF or PS)), 10B(d, n)11C and 12C(3He, αγ)11C. The following remarks on individual levels derive largely from (1965OL03, 1965RO07):
Transitions to 11Cg.s. and (2.0) are predominantly E1, fixing the parity of 11C*(7.51) as even and that of 11C*(2.0) as odd. The transition to 11C*(2.0) is not isotropic, so J ≠ 1/2; Jπ = 3/2+ or 5/2+ are possible, but if 11C*(2.0) is 1/2-, Jπ = 5/2+ is eliminated (see also 12C(3He, α)11C). The relatively large strength of the cascade transition is difficult to understand, and comparison with 11B*(8.00) suggests some deviation from charge symmetry (1965OL03, 1965RO07).
Ex = 6.91 MeV. The g.s transition is predominantly E1 so Jπ ≤ 5/2+ (1965OL03). Branching ratios favor J = 3/2 or 5/2 (1965RO07): J = 5/2 from 12C(3He, α)11C. The analogue is presumably 11B*(7.30) (1965OL03). τm < 0.16 psec (1966WA10).
Ex = 6.48 MeV. The E2 character of the g.s. transition indicates Jπ ≤ 7/2-; J = 7/2 from 12C(3He, α)11C. This level is weakly populated in 9Be(3He, n)11C. The analogue is presumably 11B*(6.74). τm < 0.25 psec (1966WA10). See also (1966GO12).
Ex = 6.34 MeV. The g.s. transition is predominantly E1 so Jπ ≤ 5/2+ (1965OL03). Relative transition strengths are consistent with J = 1/2 or 3/2 with the assumption that 11B*(6.79) is the mirror level (1965RO07). τm < 0.11 psec (1966WA10). Jπ = 1/2+ from 12C(3He, α)11C.
Ex = 4.79 MeV. Stripping results indicate odd parity, J ≤ 5/2- (1965TO06), consistent with the observed M1, E2 nature of the g.s. transition. The strength of the transition to 11C*(2.0) argues against J > 5/2. J = 3/2 from 12C(3He, α)11C.
Ex = 4.31 MeV. The M1 g.s. transition indicates Jπ ≤ 5/2-. J = 5/2 from 12C(3He, α)11C.
Ex = 2.00 MeV. The E1 transition from 11C*(7.50) fixes the parity as odd, Jπ ≤ 7/2-. Jπ = 1/2- is fixed from 12C(3He, α)11C.
In the range Ep = 0.7 to 4.7 MeV, two broad resonances are reported at 1.14 and ≈ 4.4 MeV: see Table 11.18 (in PDF or PS)) (1954DA20, 1955BA22, 1956CH20, 1957HU79, 1962OP03). At the Ep = 1.14 MeV resonance (Ex = 9.73 MeV), capture γ-rays are observed corresponding to the direct ground-state transition (relative intensity 1.0 ± 0.2) and to cascades via the states at 6.48 (0.3), 4.31 (0.18 ± 0.02) and 2.00 MeV (0.05), with (2J + 1)Γγ = 10, 1.8 and 3 eV for the ground state transition and the cascades through the 6.48 and 4.31 MeV states, respectively (1961JA11). The 6.48 MeV state decays ≈ 1/3 of the time via a cascade through the 4.31 MeV state (1961JA11). The 4.31 MeV state goes by direct ground-state decay (> 98%) while the 4.79 MeV state decays in (15 ± 5%) of the cases via the 2.0 MeV state (Eγ = (2.72 ± 0.08) + (2.05 ± 0.08) MeV) (1961DO03). See Table 11.17 (in PDF or PS)).
Ethresh. = 4880.1 ± 2.0 keV; Q0 = -4432.8 ± 1.8 keV (1966FR09). This result is 44 keV lower than the value used by (1965MA54), and considerably more accurate. We adopt (M - A) 10C = 15702.6 ± 2.0 keV for the present review.
The total (p, n) cross section has been measured to Ep = 10.6 MeV by (1963EA01): broad maxima are observed at Ep = 5.92 ± 0.02, 6.68 ± 0.04, 7.33 ± 0.05 and 7.60 ± 0.05 MeV (see Table 11.18 (in PDF or PS)). The cross section for formation of 10Cg.s. measured up to Ep = 12 MeV, shows similar behavior to 8 MeV. At Ep ≈ 8 MeV, a sharp maximum is observed. The cross section for production of 3.35 MeV γ-rays (from 10C*) does not appear to show structure for Ep = 8.5 to 12 MeV (1966SE03). See also (1959AJ76, 1963VA1C, 1965VA23).
The elastic scattering shows two conspicuous anomalies, at Ep = 1.50 ± 0.02 MeV and at 2.18 MeV, corresponding to states at Ex = 10.06 and 10.68 MeV with Jπ = 7/2+ and 9/2+ (see Tables 11.18 (in PDF or PS)) and 11.19 (in PDF or PS)). Below Ep = 0.7 MeV, the scattering can be explained in terms of pure s-wave potential scattering but the possibility of a state near Ep = 0.270 MeV (Ex = 8.95 MeV) cannot be excluded (1960OV1A, 1962OV02: Ep = 0.15 to 3.0 MeV). (1962OV02) also report evidence for a state formed by s-wave protons near Ep = 2.8 MeV. On the other hand (1962AN11) who have studied scattering to Ep = 3.5 MeV interpret the data as indicating a resonance above Ep = 3.5 MeV. See also (1951BR10, 1961RO05, 1966JA1F).
The yield of 0.71 MeV radiation, from 10B*, rises monotonically from Ep = 1.5 to 4.1 MeV (1952DA05, 1954DA20, 1957HU79, 1964BE31), and then shows resonance behavior at Ep = 4.35 ± 0.02 MeV and 5.73 ± 0.02 MeV (1962OP03: see Table 11.18 (in PDF or PS)). For Ep = 6 to 12 MeV, the cross section shows several sharp maxima superposed on a broad maximum (Γ ≈ 2.5 MeV) at Ep ≈ 7.2 MeV (1966SE03). (1966SE03) have also measured the yields of the 1.02 (10B*(1.7) → 10B*(0.7)), 1.43 (10B*(2.1) → 10B*(0.7) and 10B*(3.6) → 10B*(2.2)), 2.86 (10B*(3.6) → 10B*(0.7)) and 4.44 10B*(5.16) → 10B*(0.7)) MeV gamma rays for Ep = 4 to 12 MeV. The yields of both the 2.15 and 3.58 MeV states of 10B show a broad resonance, about 4 MeV wide, centered at Ep ≈ 8 MeV, with some fine structure superimposed. The yields of the 1.74 and 5.16 MeV states show this resonance weakly or not at all (this is also true of the neutrons in reaction 6). For the groups that show the broad resonance, the maximum cross sections vary from 20 to 160 mb and tend to increase with increasing Q. For the groups that do not show the broad resonance, the cross sections are all below 5 mb and reach their maxima in the 7 - 12 MeV region. The weak reactions are those in which the residual nucleus is left in a T = 1 state. This is explained in terms of an α + α + d + p character for the broad resonance. This suggests a significant (α + α + d) cluster structure for the 10B ground state as well as for the first few low-lying states of 10B (1966SE03, 1967WA1L).
See 9B in (1966LA04).
The ground-state yield has been obtained for Ep = 4 to 10 MeV (θ = 50°, 90°). There are slight maxima at similar energies to those in the (p, α) yield. However, the angular distributions do not vary strongly over the region covered and it is suggested that a direct interaction mechanism dominates (1963JE01). (1966SE03) report two strong maxima at Ep ≈ 4.5 and 6.5 MeV.
The parameters of observed resonances are displayed in Tables 11.18 (in PDF or PS)) and 11.19 (in PDF or PS)). The ground state (α0) α-particles exhibit broad resonances at Ep = 1.17, 1.53, 2.18, 3.0, 4.4, 5.1 and 6.3 MeV (1959AJ76, 1962OV02, 1964JE01). Alpha particles to the 0.43 MeV 7Be state (α1) and 0.43 MeV γ-rays exhibit all but the 1.2 MeV resonance (1959AJ76, 1962OP03, 1964BE31, 1964JE01, 1966SE03). Weak resonances are also reported at 2.32, 2.57 and 3.59 MeV (1964BE31). A broad maximum dominates the region from Ep = 4 MeV to about 7.5 MeV (1966SE03). See also discussion under reaction 6, and (1963VA1C).
Neutron spectra have been studied by (1959AJ76), (1952JO10, 1956CE1B, 1956CE73, 1956GR54, 1956MA83, 1957GR50, 1959NE1A, 1960MC1C, 1963OV02, 1965SI13) and others. Angular distributions, γ spectra and (n-γ) correlations are reported by (1960FE13, 1960MC1C, 1960NE17, 1961JA12, 1962FR06, 1963BR1H, 1965OL03, 1966AD1D), (1966GO12, 1966RU01, 1966WE1B, 1967DI01) and (1959AJ76). The principal results are exhibited in Table 11.20 (in PDF or PS)).
DWBA fits to the ground-state distribution are reported by (1967DI01: Ed = 5 to 7.6 MeV). At Ed = 7.6 and 9.0 MeV, the angular distributions corresponding to the first four levels match the PWBA l = 1 patterns moderately well, although the 11C*(2.0) level is relatively weak (1956CE1B, 1956CE73: 7.6 MeV) and (1956MA83: 9 MeV). For Ed = 1 to 4 MeV, levels at Ex = 6.48, 8.43 and 8.66 MeV show good patterns; 11C*(2.0, 4.3, 4.8, 6.34, 6.91) are quite weak (1960FE13, 1960NE17, 1965SI13: Ed = 5 to 8 MeV) and (1961JA12). The 11C*(2.0) is believed to have Jπ = 1/2- and is presumably formed by an exchange or spin-flip mechanism (1963AU1A). In j-j coupling, it is expected that only the levels (3/2)I, (7/2)I and (5/2)II will show large stripping widths: these are presumably 11C*(0, 6.48, 8.42) (1960BI08, 1960MA32, 1961JA12).
Neutron threshold measurements indicate levels at 8.103, 8.426 and 8.656 MeV (1955MA76: ± 8 keV; based on Qm). (1963OV02) has investigated this region with time-of-flight techniques and finds that two levels exist near Ex = 8.7 MeV, at Ex = 8.657 and 8.702 MeV. A broad level is located at Ex = 10.69 MeV (Γ ≈ 200 keV) but no evidence is found for other levels reported above Ex = 8.7 MeV. The doublet appears to correspond to the s-particle doublet in 11B*(9.19, 9.28) (1963OV02).
Angular distributions of the neutrons to the ground state of 11C and to the first five excited states have been analyzed by stripping theory [(1961HI08: E(3He) = 9.84 MeV) and (1965PA10: E(3He) = 3.5 to 10 MeV)] and the excitation energies of nine states have been determined (1961HI08): see Table 11.21 (in PDF or PS)).
The tritons corresponding to the ground state have been observed at Eα = 43 MeV (1967DE1K).
Neutron groups have been observed to 11Cg.s. and to the first excited states: see Table 11.21 (in PDF or PS)) (1965OV01). Angular distributions of the ground-state neutrons have been studied at many energies up to Ep = 18.5 MeV (1960HI04, 1961AL07, 1964AN1B, 1964SA1D, 1964ST1C, 1965WA04). See also (1956AJ22, 1961GO13, 1961TA12, 1963PA1E, 1964BA16, 1965VA23, 1966UN1A) and 12C.
At Ep = 155 MeV, deuteron groups have been observed to the ground state and to excited states of 11C at 2.0 ± 0.1, 4.9 ± 0.1 and (7.0 ± 0.2) MeV (1962RA01, 1963BA1R, 1963RA01, 1967BA2L). See also (1965DE1A, 1965KE02, 1965PU02, 1965VE1B). Angular distributions have been measured at Ep = 19-20 MeV (1962WA31), 27.5 MeV (1967GL01), 30 MeV (1967CH15), 31.1 and 33.5 MeV (1967GR1M), 36 MeV (1965KE02), 40 MeV (1963KA26, 1966SH1A), 45 MeV (1966MA2B), 54.9 MeV (1968TA1P), and 60 MeV (1965IS06). For spectroscopic factors, see (1967BA2L). See also (1956SE1A, 1959GR1B, 1960RA12, 1961CL09, 1962BE1H, 1963CL07, 1963IS1B, 1963MA1J, 1964JA1C, 1964SH07, 1965GL1E, 1967HO1M, 1967TO1D).
Ten states of 11C have been observed at Ed = 50 MeV. The angular distributions are identical with those seen in the mirror reaction 12C(d, 3He)11B to analogue states (1966CH1K): see 11B. At Ed = 28.5 MeV the (d, t) and (d, 3He) cross sections to the ground states of the mirror nuclei 11C and 11B are equal (1966DE1C). See also (1959VL23, 1967FI1G), and 14N in (1970AJ04).
Angular distributions of alpha particles to the ground state have been observed at E(3He) = 1.8 to 5.4 MeV (1964KU05), 2.4 to 4.5 MeV (1963LU05), 4.8 to 5.9 MeV (1966BL01), 8.5 to 10.0 MeV (1966SC22), 6.0, 8.8, 9.4 and 10.1 MeV (1960HI07), 16 to 18 MeV (1967GR1L, 1967GR1N), 24.8 MeV (1967HA21), 26 to 33 MeV (1963PA1G), and 26 MeV (1966DA1H). The α1 distributions (to the 2 MeV state) have been investigated at E(3He) = 4.2, 4.9, 5.6, 6.0, 8.8, 9.4, 10.1, 16 to 18 MeV (1960HI07, 1964KU05, 1966BL01, 1967GR1L, 1968GR1G). Angular distributions at the higher energies are consistent with ln = 1 for both α0 and α1 (1960HI07). See also (1966SC22). The energy of the first excited state is Ex = 1.990 ± 0.010 (1959PO61), 2.000 ± 0.010 (1960HI07), 1.999 ± 0.004 MeV (1968EA03). See also (1961CA1D, 1962AG01, 1962CA29, 1962GA17, 1962WE1C, 1963PA15, 1964BE1K, 1965GR1R).). See also 15O in (1970AJ04) and (1966HA1Q, 1967BR1N).
Studies of α-γ correlations have been carried out by (1965WA06: E(3He) = 4.7 MeV), (1965NE06, 1965SC1D: E(3He) = 5.1 MeV), (1967BL22: E(3He) = 9 MeV), (1966GA19: E(3He) = 10 MeV), and (1968EA03: E(3He) = 6 to 12 MeV) with the following results (1968EA03) (see also 9Be(3He, n)11C and Table 11.17 (in PDF or PS)):
Ex = 8.42 MeV. This level is unbound Γγ/Γ = 0.2 ± 0.1.
Ex = 7.51 MeV. For the ground-state transition, the α-γ correlation permits J = 3/2 or 5/2. With the J = 5/2 assignment, an unreasonable M2 enhancement is required, therefore Jπ = 3/2+ and x(≡ (L + 1)/L amplitude) = -0.04 ± 0.04 (1968EA03). The correlation in the cascade transition excludes Jπ = 3/2- for 11C*(2.0) and indicates Jπ = 1/2-, x = 0.0 ± 0.03 (1968EA03).
Ex = 6.91 MeV. The correlation analysis gives J = 5/2, x = 0.02 ± 0.03; J = 1/2 and 3/2 are eliminated.
Ex = 6.48 MeV. Analysis of α-γ correlation gives J = 7/2, x = -0.01 ± 0.06.
Ex = 6.34 MeV. The cascade transition is via 11C*(2.0) and not 11C*(4.31). From 9Be(3He, n)11C, Jπ = 1/2+ or 3/2+. For Jπ = 3/2+ correlation analysis requires an excessive M2 admixture. The angular distribution of α's at E(3He) = 11.0 MeV gives an l = 0 pattern: Jπ = 1/2+.
Ex = 4.79 MeV. The decay is to 11Cg.s. and (2.0). With Jπ = 1/2- for 11C*(2.0), the correlation analysis eliminates Jπ = 5/2- and 1/2- and gives for Jπ = 3/2-, x(g.s.) = -(0.04 ± 0.04) or -(3.28 ± 0.49), and x(4.8 → 2.0) = +(0.03 ± 0.05) or +(1.60 ± 0.12). See also (1966GA19, 1967BL22).