A = 11B (1968AJ02)

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¹¹B (1968AJ02)

(See Energy Level Diagrams for ¹¹B)

GENERAL: See Table 11.3 [Table of Energy Levels] (in PDF or PS).

Shell model: (1956KU1A, 1957KU58, 1960BI07, 1960TA1C, 1961BA1E, 1961BA1F, 1961KO1A, 1961KU1C, 1961TR1B, 1961UM1A, 1964AM1D, 1964NE1E, 1965CO25, 1965FA1B, 1965FA1C, 1966HA18, 1966MA1P, 1967CO32, 1967FA1A, 1968KU1D).

Collective model: (1959BR1E, 1961CL10, 1962CL13, 1964MA1G, 1965NE1B, 1966EL08, 1966MI1F, 1967RI1B, 1968GO01).

Ground state properties: (1962BE1D, 1963BE36, 1964LI14, 1964LI1B, 1964ST1B, 1965HU13, 1966RI12, 1966WI1E, 1967BA78, 1967RH1C, 1967SH05, 1968BA2G).

Other: (1963SE1K, 1964OL1A, 1964TH03, 1966WI1F, 1967BA1E, 1967PO1J).

μ = +2.6885 nm (1965FU1G);

Q = +0.04 b (1965FU1G), +0.0372 b (1966ST12).

1. ⁶Li(⁶Li, p)¹¹B Q_m = 12.220

Angular distributions of the protons to ¹¹B states below E_x = 9.3 MeV have been measured for E(⁶Li) = 2.4 to 9.0 MeV (1966KI09). Gamma spectra have been studied at E(⁶Li) = 2.6 MeV. Relative populations to ¹¹B levels are reported (1962BE24). See also (1960SH01, 1962BE16, 1963LE09).

2. ⁷Li(α, γ)¹¹B Q_m = 8.664

Three resonances for capture radiation are reported at E_α = 401, 819 and 958 keV, corresponding to ¹¹B levels at 8.92, 9.19 and 9.27 MeV: see Table 11.4 (in PDF or PS). No others appear for E_α < 2.5 MeV (1954HE22). See also (1960SI02). Angular distributions and correlations have been studied by (1959JO25, 1962GR07) with the following conclusions:

E_x = 9.27 MeV. The angular distribution of the ground-state transition requires J^π = 3/2^± or 5/2^±. Correlations in the cascades eliminate all but J^π = 5/2⁺, formed by p-wave. θ²_α ≈ 0.1. The g.s. radiation is E1, Γ_γ = 0.6 eV [cm].

E_x = 4.44 MeV. The angular distribution in the cascade 9.28 → 4.44 → g.s. determines J = 5/2; stripping results give odd parity. The E2/M1 amplitude ratio in the transition to the ground state is x = -0.2 ± 0.02^†.

^† The sign and magnitude are in good accord with IPM, if collective enhancement is included (PO66E).

E_x = 6.74 MeV. Angular distributions and branching ratios indicate J^π = 7/2^±, with 7/2^- favored (and indicated by stripping). The transition 6.74 → 4.44 is either pure M1 or pure E2. The branching ratio 6.74 → g.s./6.74 → 4.44 is 1.75 ± 0.1 (1962GR07), 4.9 (1958FE70). See also ⁹Be(³He, p)¹¹B.

E_x = 9.19 MeV. Angular correlations in the cascade transitions require J^π = 7/2^±; the ground-state transition fixes J^π = 7/2⁺ formed by f-waves, θ² = 0.04, with an M2/E3 amplitude of 0.9 and an E3 strength of 6 to 17 Weisskopf units. See, however, ⁹Be(³He, p)¹¹B.

E_x = 8.93 MeV. The angular distribution of the ground-state transition yields J^π = 3/2⁺ or 5/2^±. Consideration of the transition strength favors 5/2^-.

3. ⁷Li(α, n)¹⁰B Q_m = -2.792 E_b = 8.664

Observed resonances are listed in Table 11.5 (in PDF or PS). Comparison with ¹⁰B(n, α)⁷Li indicates that the resonances at E_α = 5.15 MeV (E_x = 12.0 MeV) has J^π = 3/2^- or 5/2⁺, Γ_n ≈ 20 keV, Γ_α ≈ 300 keV formed by l_n = 0 or 1 (1959GI47).

4. ⁷Li(α, p)¹⁰Be Q_m = -2.564 E_b = 8.664

See ¹⁰Be in (1966LA04).

5. ⁷Li(α, t)⁸Be Q_m = -2.562 E_b = 8.664

See ⁸Be in (1966LA04).

6. ⁷Li(α, α)⁷Li E_b = 8.664

Elastic scattering has been studied for E_α = 1.6 to 12 MeV by (1966CU02). The inelastic scattering, leading to ⁷Li*(0.48) has been studied by (1954HE22: E_α = 1.5 to 3.5 MeV), (1954LI48: E_α = 1.2 to 2.8 MeV), (1957BI84: E_α = 1.5 to 6.0 MeV), (1966CU02: E_α = 1.6 to 12 MeV); see Table 11.6 (in PDF or PS).

A detailed fit to the elastic and inelastic data below the first (α, n) threshold, E_α = 4.38 MeV, requires at least seven resonances (Table 11.7 (in PDF or PS)) (1966CU02). For the 9.87 MeV level, the weakness of the elastic effect eliminates J = 1/2, while the reduced width in the inelastic channel eliminates J^π = 3/2^- and J ≥ 5/2; thus J^π = 3/2⁺. Of the next two levels, E_x = 10.25 and 10.32 MeV, the first influences mainly the inelastic yield, while the second (seen also in ¹⁰B(d, p)¹¹B) appears only in the elastic scattering. For the lower, possible assignments are J = 1/2^±, 3/2^± or 5/2^±, with 3/2^- preferred; the upper has J^π = 5/2^- or 7/2^-. The narrow level at E_x = 10.60 MeV, also seen in ⁹Be(³He, p)¹¹B shows no effect on elastic scattering at θ_cm = 141°, indicating l = 3; J^π = 7/2⁺ is preferred, with J = 5/2⁺ possible. A broad maximum in the inelastic cross section at E_α ≈ 3.6 MeV may indicate a level at E_x = 11.0 MeV. An underlying general rise is ascribed to a J^π = 1/2⁺ level, with Γ ≈ 4.4 MeV. With this assumption, the elastic yields require J^π = 3/2^- or 5/2^- for the 11.0 MeV level, with 5/2^- preferred. The narrow level at E_α = 4.1 MeV, E_x = 11.27 MeV, appears only weakly in the inelastic cross section; it is seen also in ⁹Be(³He, p)¹¹B. The elastic scattering indicates J^π = 7/2⁺ or 9/2⁺.

Analysis of the structure above E_α = 4.38 MeV is rendered difficult by the increasing number of open channels. Anomalies observed at E_α = 4.4, 5.5, 7.2, 7.8 and 9.95 MeV coincide with thresholds in ⁷Li(α, n)¹⁰B* (1966CU02).

7. ⁷Li(⁶Li, d)¹¹B Q_m = 7.192

The lifetimes of ¹¹B*(6.79, 7.30, 8.00) are less than 50 fsec (1967THZX). Gamma spectra indicate that all bound levels are populated at E(⁶Li) = 2.6 MeV (1962BE24). Angular distributions are not symmetric about 90°; an α-transfer process is suggested (1961MO02). Angular distributions have also been obtained at E(⁷Li) = 3.78 to 5.95 MeV for the deuterons to ¹¹B*(0, 2.12, 4.44, 5.02, 6.74 + 6.79, 7.30) (1967KI03), and at E(⁷Li) = 3.3 MeV (¹¹B* = 0, 2.12, 4.44, 5.02) (1967GA06). See also (1966RO1E, 1966RO1F).

8. ⁷Li(⁷Li, t)¹¹B Q_m = 6.197

Triton-gamma coincidence studies yield the following branching ratios: ¹¹B*(5.02) → g.s. (85 ± 5%), 5.02 → 2.12 (15 ± 5%), 5.02 → 4.44 (< 5%), 4.44 → g.s. (100%), 4.44 → 2.12 (< 5%) (1963CA09): see Table 11.9 (in PDF or PS). The lifetimes of ¹¹B*(6.79, 7.30, 8.00) are less than 0.5 msec (1967THZX). See also (1961MO02, 1962BE24, 1966RO1E, 1966RO1F, 1967WY1B).

9. ⁹Be(d, γ)¹¹B Q_m = 15.819

Radiative transitions have been observed to ¹¹B*(0, 2.12, 4.44 + 5.02). For E_d = 0.5 to 1.4 MeV, the intensity ratios are 1:(0.30 ± 0.08):(0.78 ± 0.15). At E_d = 1.4 MeV, σ(g.s.) = 4.3 ± 0.8 μb: the g.s. radiation is isotropic at E_d = 0.7 and 1.2 MeV (1966ZI01). The 90° differential cross section has been measured for E_d = 0.5 to 5.5 MeV for ground state γ-rays: no resonance structure is observed. The peak cross section is about 8 μb. Angular distributions are anisotropic for the higher bombarding energies (1963SU09, 1966SU05, 1966SU1C). See also (1960SU09, 1961SU17).

10. ⁹Be(d, n)¹⁰B Q_m = 4.363 E_b = 15.819

The cross section follows the Gamow function for E_d = 70 to 110 keV (1955RA14). The fast neutron and γ-ray yield rise smoothly to E_d = 1.8 MeV except for a possible "resonance" at E_d ≈ 0.94 MeV (the fast neutron yield then remains approximately constant to 3 MeV) (1949EV1A, 1955BO1A, 1957SH65, 1960BA46, 1963KO15, 1965SI12). This resonance is observed in the total neutron yield and in the yield of the fast neutrons to each of the first five states of ¹⁰B (1957SH65; see however, (1959NE1A)). The polarization angular distributions of the neutrons to ¹⁰B*(0, 0.72, 1.74, 2.15) have been measured at E_d = 1.57, 2.06 and 2.48 MeV (1967MI1F). See also ¹⁰B in (1966LA04) and (1965BU10, 1967SC43).

11. (a) ⁹Be(d, p)¹⁰Be Q_m = 4.590 E_b = 15.819
(b) ⁹Be(d, α)⁷Li Q_m = 7.154
(c) ⁹Be(d, t)⁸Be Q_m = 4.592
(d) ⁹Be(d, 2α)³H Q_m = 4.687
(e) ⁹Be(d, tn)⁷Be Q_m = -14.304

(1952CA19) reports broad maxima in the 90° yield of the ground-state protons at E_d ≈ 0.9, (1.3) and 2.1 MeV (see also (1961IS01)). (1957MC35) observe broad resonances at 1.3 and possibly at 1.8 MeV in the yield of 3.37 MeV γ-rays (from ¹⁰Be*) in the range E_d = 1.0 to 5.6 MeV. No resonances are observed in the yield of 6 MeV γ-rays for E_d = 2.0 to 5.6 MeV. The yields of protons (at 40°) to the ground state and to the first excited state both decrease slowly and monotonically with energy in the range E_d = 3.8 to 6.3 MeV (1961RE03, 1961RE04). See also (1962BI11, 1966AM1C, 1967FA03) and (1959AJ76). Polarization of the protons has been studied at E_d = 1 to 6 (1967BL02), 1.6 (1961VA03), 6 (1960HI09), 7.8 (1962GR14), 7.8, 8.9, 10 and 13.8 (1967SA07), 8.9 (1959HI1E), 10 (1962AL10), 11 (1964PA1E), 13.8 (1962PA12), 15 (1964RE04) and 21 MeV (1963BO1J). See also (1960LU04, 1966MI1E).

The yields of α-particles (reaction (b)) to the ground and first excited states have been measured in the range E_d = 0.5 to 2.3 MeV. There is no clear indication of resonance structure. The cross sections for the two groups are quite similar but their angular distributions are different over the entire energy range (1962BI11). Yields have also been measured for E_d = 8 to 12.4 MeV (α₀, α₁) and 9 to 12.4 MeV (α₂) (1966DO1A). See also ⁷Li in (1966LA04) and (1966AM1C).

The cross section for reaction (c) has been measured for E_d = 0.15 to 0.62 MeV by (1952DE24), for E_d = 0.6 to 1.5 MeV by (1955JU10, 1955JU1B), for E_d = 3.8 to 6.3 MeV by (1961RE03, 1961RE04) and at several energies in the range E_d = 3 to 19 MeV by (1955HE83). See also (1962BI11, 1966AM1C). The forward yield of tritons shows a peak at E_d = 1.38 MeV, and possibly, at 0.87 MeV (1955JU10, 1955JU1B, 1958JU38). In the range E_d = 3.8 to 6.3 MeV, the 40° differential cross section for ground state protons is approximately constant (1961RE03, 1961RE04).

The direct three-body reaction [reaction (d)] does not appear to occur (1953GE01). For reaction (e) see (1955HE83). See also (1962WI15, 1965MA57).

12. ⁹Be(d, d)⁹Be E_b = 15.819

The differential cross section for elastic scattering has been measured for E_d = 0.4 to 1.8 MeV (θ = 90°, 126°, 163.5°). No anomalies were observed (1963RE16: see, however, (1956JU17)). Asymmetries have been measured with polarized deuterons at E_d = 11.7 MeV (1966DO1B). See also (1960BU25, 1963NE1H) and ⁹Be in (1966LA04).

13. ⁹Be(t, n)¹¹B Q_m = 9.561

See (1962SE1A).

14. ⁹Be(³He, p)¹¹B Q_m = 10.325
Q₀ = 10.344 ± 0.013 (1964MA57);
Q₀ = 10.3221 ± 0.0023 (1967OD01).

Proton groups have been observed to 23 states of ¹¹B: see Table 11.8 (in PDF or PS) (1959HI69, 1963GR20, 1966BR18). Angular distributions of many of these protons groups have been observed at E(³He) = 1.0 to 3.0 MeV (1967CO03), 2 MeV (1963WE08), 4.5 MeV (1959WO53), 5.7 MeV (1959HI69) and 8.8 and 10.2 MeV (1960HI08). Of the first ten groups, seven show stripping patterns: the exceptions are ¹¹B*(6.74, 7.30, 8.00) (1960HI08). The narrow level at E_x = 12.565 MeV does not appear in ¹⁰B(d, p)¹¹B and may therefore have T = 3/2 (1963GR20: see, however, ⁷Li(α, α)⁷Li). See also (1959AJ76) and ¹²C.

Gamma-ray branching ratios and multipolarities for ¹¹B levels up to E_x = 9.19 MeV have been extensively studied by (1958FE70, 1961DO03, 1964AL22, 1965OL03): see Table 11.9 (in PDF or PS). The following remarks on individual levels derive largely from (1965OL03): see also ¹⁰B(d, p)¹¹B.

E_x = 9.19 MeV. Γ_γ/Γ = 0.1^+0.2_-0.05. From ⁷Li(α, γ)¹¹B, Γ_s = 0.275 eV, J^π = 7/2⁺. Then Γ_α = 2.8^+2.8_-1.8 eV, Γ_γ = 0.3^+0.1_-0.01 eV. The ground-state transition of 0.9% is 0.45 E3 and 0.55 M2 leading to M2 and E3 strengths of 0.3 ± 0.1 and 78 ± 26 Weisskopf units, respectively.

E_x = 8.93 MeV. Γ_γ/Γ = 1.08 ± 0.12. From ⁷Li(α, γ)¹¹B, J^π = 3/2⁺, 5/2⁺, 5/2^-. The internal pair correlation excludes J^π = 3/2⁺, 5/2⁺, and confirms 5/2^-. The ground-state transition is then M1 with 0.6% E2. With Γ_s = 0.025 eV, 0.025 ≤ Γ_α ≤ 0.03 eV, Γ_γ ≥ 0.15 eV. See (1966GO12) and ¹¹B(e, e')¹¹B*.

E_x = 8.57 MeV. Correlation of internal pairs indicate that the g.s. transition is M1 + E2 or E1 + M2, J^π ≤ 5/2⁺ or ≤ 7/2^-; the lifetime to ¹¹B*(2.12) excludes 7/2^-. If the level has even parity, the required M2 admixture is excessive. J^π ≤ 5/2^- is favored. The odd parity assignment agrees with stripping results in the present reaction, but disagrees with the results from ¹⁰B(d, p)¹¹B. See ¹¹B(e, e')¹¹B*.

E_x = 8.00 MeV. Transitions to ¹¹B_g.s. and (2.12) are predominantly E1; thus E_x = 8.00 MeV has even parity, and the odd parity of ¹¹B*(2.12) is confirmed. The transition to ¹¹B*(2.12) is not isotropic, so J^π = 3/2⁺. Comparison of branching ratios with analogous case in ¹¹C suggests some deviation from charge symmetry.

E_x = 7.30 MeV. The g.s. transition is mainly E1, so J^π ≤ 5/2⁺. The assignment 1/2⁺ is excluded by the strength of (7.30 → 4.44).

E_x = 6.79 MeV. The allowed β-decay from ¹¹Be indicates J^π ≤ 7/2⁺. The relatively strong γ-branch to ¹¹B*(2.12) favors 1/2⁺, 3/2⁺. (1968EA03) finds that all γ's from this level are isotropic, suggesting J^π = 1/2⁺, but not excluding 3/2⁺.

E_x = 6.74 MeV. From ⁷Li(α, γ)¹¹B, J = 7/2. Internal pairs indicate practically pure E2 g.s. radiation: J^π = 7/2^-.

E_x = 5.02 MeV. Stripping work fixes the parity as odd. The internal pair correlations permit M1, E2 for the g.s. transition, J^π ≤ 7/2^-; the lifetime τ_m < 0.5 psec excludes J = 7/2. The comparatively strong branch to ¹¹B*(2.12) argues against J = 5/2, therefore J^π1/2^- or 3/2^- (1961DO03). Angular correlation studies indicate a P₂(cosθ) term of (10 ± 5)%; if this term is real, J ≠ 1/2 (1968EA03).

E_x = 4.44 MeV. The g.s transition is predominantly M1, consistent with J^π = 5/2^- (see ⁷Li(α, γ)¹¹B).

E_x = 2.12 MeV. The lifetime (4.6 fsec) demands dipole radiation. The E1 transition from ¹¹B*(8.00) requires odd parity; the weakness of the 4.44 (5/2^-) to 2.12 transition leaves only J^π = 1/2^- (1961DO03).

The properties of the first five levels of ¹¹B are consistent with ascription to p⁷; there is evidence that ¹¹B*(8.93) also belongs to p⁷, while ¹¹B*(8.57) appears more likely to belong to a higher configuration.

See also (1960EL1C, 1961EL1A, 1962WE1C, 1963VA16, 1966WA1C).

15. ⁹Be(α, d)¹¹B Q_m = -8.028

At E_α = 28.3 MeV, differential cross sections have been measured (θ = 15° to 47°) for the deuteron groups to ¹¹B*(0, 2.12, 4.44, 5.02) (1965KA14). See also (1955RA41, 1962WE1C, 1967ZE1A).

16. ⁹Be(⁶Li, α)¹¹B Q_m = 14.347

Angular distributions and total cross sections have been determined for seven α-groups. In the range E(⁶Li) = 3 to 4 MeV, the distributions change only slowly. A direct interaction mechanism is suggested (1961EL1A, 1961HO19, 1961LE01, 1961LE09, 1961RU1B, 1966SA04). Gamma raditation has been studied by (1963NO02, 1964CA18). Evidence of participation of a level near E_x = 12.5 MeV is reported by (1961CO33, 1961LE08). See also (1963BA1T, 1966BA1T, 1966RO1E, 1966RO1F, 1966RO1H).

17. (a) ⁹Be(⁷Li, αn)¹¹B Q_m = 7.094
(b) ⁹Be(¹⁴N, ¹²C)¹¹B Q_m = 5.547

For reaction (a) see (1964CA18). For reaction (b) see (1964BO1M).

18. ¹⁰B(n, γ)¹¹B Q_m = 11.456

The thermal neutron capture cross section is 0.5 ± 0.2 b. The direct ground-state decay has Γ_γ = 0.01 eV (1957BA18). See also (1959AJ76).

19. ¹⁰B(n, n)¹⁰B E_b = 11.456

The thermal scattering cross section (bound) for B is 4.4 ± 0.2 bn (1958HU18). The coherent scattering amplitude (bound) for ¹⁰B is a = +1.4 ± 1.5 fm. Combined with the potential scattering amplitude of 5.0 fm (derived from (1955WI25)), this low value indicates a resonance level above the neutron binding energy (1965DO14, 1966DO11). According to (1960BI04) the total cross section σ_s + σ_n,α fits the expression σ = 2.43 + 642/E^1/2 up to 70 keV; the 1/ν term is ascribed to σ_n, α and σ_s is taken to be 2.43 b: see also (1964ST25, 1965MO1J). Elastic scattering differential cross sections at E_n = 0.55, 1.0 and 1.5 MeV are analyzed in terms of phase shifts by (1955WI25): only s-waves appear at E_n = 0.55 MeV.

The total cross section (including σ_n,α) shows broad maxima at E_n = 1.9 and 2.8 MeV (1951BO45) and at 4.3 MeV (1961FO07); an additional peak at E_n = 0.2 MeV may be indicated (1951BO45). Above E_n = 5.5 MeV, σ_tot is constant at 1.5 b to 16 MeV (1961FO07, 1964ST25). Polarization and differential cross sections have been measured for 70 energies in the range E_n = 0.075 to 2.25 MeV. The polarization is nearly constant for E_n = 0.5 to 2.25 MeV and shows no appreciable effect of the resonance at E_n = 1.9 MeV. Most of the width of this resonance appears to be in the α-channel (1967LA1N). See also (1959MA1C, 1960AN14, 1966AG1A, 1967CI1B) and (1959AJ76).

20. ¹⁰B(n, n')¹⁰B* E_b = 11.456

The yield of 0.7 MeV γ-rays has been studied from threshold to E_n = 5.2 MeV: resonances are observed at E_n = 1.93, (2.6), 3.31, 4.1 and 4.73 MeV (see Table 11.10 (in PDF or PS)) (1960DA08). See also (1964ST25) and (1963GL1F, 1963GO1M).

21. ¹⁰B(n, p)¹⁰Be Q_m = 0.228 E_b = 11.456

The thermal cross section is < 0.2 b (1958HU18); the cross section for fast pile neutrons is 3 mb (1948EG1A).

22. ¹⁰B(n, d)⁹Be Q_m = -4.363 E_b = 11.456

See (1954RI15). See also (1963GO1M).

23. ¹⁰B(n, t)⁸Be Q_m = 0.229 E_b = 11.456

The ¹⁰B(n, t)⁴He⁴He cross section has been measured for E_n = 1.4 to 8.2 MeV by (1961DA16). Fluctuations in the cross section are observed at some of the resonant energies in the ¹⁰B(n, α) reaction: see Table 11.10 (in PDF or PS). See also (1964ST25, 1966JE1B).

24. ¹⁰B(n, α)⁷Li Q_m = 2.792 E_b = 11.456

The "recommended" value of the thermal isotropic absorption cross section is 3837 ± 10 b (1964ST25), which includes recent determinations by (1963PR11: 3837 ± 9 b; (1961ME02): 3843 ± 17 b; (1960SA13, 1961SA02): 3838 ± 11 b; (1960SC15): 3848 ± 38 b). See also (1964AL05, 1965WY1C). The cross section follows the 1/ν law from 4 meV to 500 keV (1964ST25, 1965MO1J, 1966CO1K, 1967CO1N) except for a weak resonance at E_n = 230 keV (1966MO09). There appears to be some discrepancy between reported values of σ_abs and σ(n, α) (1966MO09).

Observed resonances are listed in Table 11.10 (in PDF or PS) (1951PE18, 1957BI84, 1961DA16). Comparison of σ(n, α) and σ(n, n), at the E_n = 0.53 MeV resonance indicates J^π = 1/2⁺, 3/2^±, or 5/2^± . For the E_n = 1.86 MeV resonance, the minimum spin assignment consistent with the observed cross section is J^π = 11/2⁺ (1961DA16). The ratio of ground-state to excited state transitions varies monotonically with energy although the 0.53 MeV resonance appears to influence the cross-section ratio to some extent: see (1959AJ76, 1960YO02, 1963MA39, 1965MA65). Recent determinations of the branching ratio for thermal neutrons yield (6.50 ± 0.03)% (see (1966TO01)), (6.70 ± 0.2)% (1966MA2P) for the ground state function. At E_n = 0.16 MeV, the ratio is (8.4 ± 0.5)% (1966MA2P).

See also (1957SE1B, 1961BE24, 1961MA1F).

25. ¹⁰B(d, p)¹¹B Q_m = 9.231

Proton groups reported by (1951VA1A, 1953EL12, 1961JA23, 1966BR18) are listed in Table 11.11 (in PDF or PS). Angular distributions have been studied at many energies: see (1959AJ76) and (1960HA08: 0.17 to 0.25 MeV), (1957SJ66: 0.8 MeV), (1961RE01: 1.2 MeV), (1959GO69, 1960GO14: 1.25 MeV), (1967PO01: 1.75 to 3.0 MeV), (1965LE1B: 2 to 12 MeV), (1961PU1B: 3.0 MeV), (1960GO11, 1960GO25: 4.6 MeV), (1963MO07: 6 MeV), (1960BI08: 7.8 MeV), (1958ZE01: 8.1, 9.2, 10 MeV), (1962HI07: 10.1 MeV), (1960TA27: 11.4 MeV), (1967MO1Q: 12 MeV), (1965BA31: 13.5 MeV), (1961ZE02: 12.5, 15.5, 18.5, 21.5 MeV) and (1962SL04: 28 MeV).

The lowest five levels are formed by l_n = 1, except for ¹¹B*(2.12) which appears to involve a spin-flip process (1957WI26, 1958EV01, 1958HE47, 1961LE1F). They are presumed to comprise the set 3/2^-, 1/2^-, 5/2^-, 3/2^-, 7/2^- expected as the lowest p⁷ levels (a/K ≈ 4.0) (1956KU1A, 1960BI08, 1965OL03). There is some disagreement about the parities of ¹¹B*(8.57, 8.93): see ⁹Be(³He, p)¹¹B and (1966GO12, 1967PO01). The levels at 9.19 and 9.28 MeV, J^π = 7/2⁺ and 5/2⁺, respectively, show strong l = 0 stripping and are ascribed to capture of a 2s neutron by ¹⁰B (1960BI07, 1960BI08, 1967PO01). See also (1960MA32, 1964BA1G, 1967BA2J, 1967MO1N, 1967ST1H).

Studies of (p, γ) correlations are reported by (1959CR1A, 1959GA05, 1959GO69, 1960CR1A, 1960GO11, 1960GO14, 1960GO25, 1961RE01, 1965OL03, 1966GO1N: see also (1959AJ76)). The principal results are exhibited in Table 11.9 (in PDF or PS) and are discussed in reaction 14.

(1963GR20: E_d = 10.0 MeV) report that the 11.27 MeV state is populated in this reaction while the narrow 12.57 MeV state observed in ⁹Be(³He, p)¹¹B is not seen. This suggests T = 1/2 and 3/2, respectively, for these two states. See, however, ⁷Li(α, α)⁷Li.

Polarization studies are reported by (1958HE47, 1959HI1E, 1960ER1A, 1960TA27, 1961ZI02, 1962PA12, 1962TA13, 1962ZI01, 1963BO1J, 1963ER1A, 1964BE08, 1964PA1E, 1965SZ01, 1965ZI1A, 1966BA2V).

26. ¹⁰B(t, d)¹¹B Q_m = 5.199

At E_d = 5.5 MeV, deuteron groups are observed to the ground state of ¹¹B and to states at E_x = 2.126, 4.449, 5.027, 6.769, 6.806 and 7.301 MeV (± 10 keV). All the angular distributions appear to be characteristic of l_n = 1 (1961BA10). See also (1963HO19, 1963KN02, 1967BI1E) and ¹³C in (1970AJ04).

27. ¹⁰B(α, ³He)¹¹B Q_m = -9.122

Not reported.

28. ¹⁰B(¹⁴N, ¹³N)¹¹B Q_m = 0.903

See (1963TO1D, 1963TO1E, 1966CO27, 1966GA04, 1967CO1T).

29. ¹¹Be(β^-)¹¹B Q_m = 11.513

The decay properties of ¹¹Be are exhibited in Table 11.12 (in PDF or PS). The transition energy to the ground state is E_{β_(max)} = 11.48 ± 0.15 MeV; τ_1/2 = 13.57 ± 0.15 sec, log ft = 6.77 (1958AL96, 1959WI49), τ_1/2 = 14.1 ± 0.3 sec (1958NU40). The small ft values of the transitions to the 3/2⁺ states at 6.79 and 8.00 MeV indicate even parity [J = 1/2, 3/2 or 5/2] for the ground state of ¹¹Be (1961DO03, 1964AL22).

30. ¹¹B(γ, γ)¹¹B

Mean gamma widths of low-lying levels obtained by resonance scattering and transmission studies are listed in Table 11.13 (in PDF or PS). M1 transition strengths calculated in intermediate coupling are given by (1965CO25).

From a threshold determination, (1965SC04) finds E_x = 2124 ± 3 keV for the first excited state. (1959HA1J) report (2J + 1) Γ_γ = 0.6 ± 0.1 eV for ¹¹B*(9.19): see, however, ⁷Li(α, γ)¹¹B. Resonance scattering from levels st 4.4, 5.0, 7.3 and 8.8 MeV is reported by (1962SE02). See also (1959FA1A, 1960BO23, 1960RE05, 1962BO17, 1964LO1C, 1967LO1B).

31. ¹¹B(γ, n)¹⁰B Q_m = -11.456

The cross section shows many peaks in the range E_γ = 12 to 28 MeV. The integrated cross section to 29 MeV is 68.6 ± 4 MeV · mb (1965HA19). See also (1961BA1D, 1963CO1D).

32. (a) ¹¹B(γ, p)¹⁰Be Q_m = -11.228
(b) ¹¹B(γ, d)⁹Be Q_m = -15.819

See (1961DO08, 1962CH26, 1962LI13, 1962VO1C, 1963KI1C) for reaction (a), and (1962CH26, 1962VO1C, 1963BA1K) for reaction (b).

33. (a) ¹¹B(γ, t)⁴He + ⁴He Q_m = -11.132
(b) ¹¹B(γ, α)⁷Li Q_m = -8.664

See (1955AJ61, 1959AJ76, 1962VO1C).

34. ¹¹B(e, e)¹¹B

The charge-scattering radius is 1.55 fm (1959ME24). Magnetic elastic scattering at θ = 180° shows strong M3 effects: the derived ratio of static M3/M1, 2.9 ± 0.2 fm², suggests a j-j coupling scheme for ¹¹B_g.s. (1966RA29). The quadrupole contribution to the elastic form factor is best accounted for by the undeformed shell model, Q = 3.72 (± 20%) b, r(r.m.s.) = 2.42 fm (1966IS1A, 1966ST12). See also (1963GO04, 1963GU1A, 1965GO1K, 1965GR18, 1965RA1C, 1965VA1G).

Ground-state transition widths for various excited states determined by inelastic scattering are listed in Table 11.13 (in PDF or PS) (1962ED02, 1966KO08, 1966SP02, 1967SP02). For ¹¹B*(8.57), the dependence of the transition probability on q² indicates an E2-M1 mixture: hence the parity is odd, J ≤ 5/2. The observed γ-width if ¹¹B*(8.93) implies Γ_α = 0.03 eV (compare ⁹Be(³He, p)¹¹B (1966SP02)). See also (1962BA1D, 1964BR1N, 1966RI1G, 1967KA1A, 1967LE1E).

35. ¹¹B(n, n')¹¹B*

See (1955GR18, 1961LI04, 1962TE05, 1963OP1A, 1966FR18).

36. (a) ¹¹B(p, p')¹¹B*
(b) ¹¹B(p, 2p)¹⁰Be Q_m = -11.228

Study of the pair line spectrum of the 2.12 MeV γ-ray establishes that there is no parity change between the ground and first excited states: therefore the parity of the excited state is odd (1963WI01; see also (1962GO09, 1963SC33)). The 2.12 MeV excited state decays by emission of a 2.134 ± 0.005 MeV γ-ray (1957MC35): it exhibits < 2.0 × 10^-3 part of circular polarization; this observation places an upper limit of F² ≲ 1 × 10^-7 for the intensity of the parity non-conserving part of the wave function (1958WI41).

At E_p = 185 MeV, proton groups are observed to ¹¹B levels at 2.2 ± 0.1, 4.5 ± 0.1, 5.1 ± 0.15, 6.8 ± 0.1 (probably corresponds to ¹¹B*(6.74)), 7.4 ± 0.3, 8.95 ± 0.15, ≈ 9.8, 10.5 ± 0.2, 11.9 ± 0.2, 13.0 ± 0.2 (Γ ≈ 0.4 MeV) and 14.5 ± 0.4 MeV (1965HA17). The state at E_x = 6.79 MeV is not reported by (1965HA17) or by (1964NE06). Assuming that the (p, p') transitions involve mainly E2, Γ(E2↓) is 22 ± 9 meV for ¹¹B*(4.44) and 90 ± 40 meV, for ¹¹B*(6.74) (1964JA03). See also (1965JA1A).

See also (1959EG1C, 1959JO43) for polarization studies; (1961KO08, 1962KI02, 1965HU10) for angular distributions at E_p = 5.8 to 7.5 MeV and (1959EG20, 1959TO1A, 1961CL09, 1962CL13).

For reaction (b) see (1964LI1D, 1964TI02, 1966JA1A, 1967JA1E, 1968JA1G) and ¹⁰Be in (1966LA04).

37. ¹¹B(d, d)¹¹B

The angular distribution of elastically scattered deuterons has been determined at E_d = 11.8 MeV and analyzed by the optical model (1967FI07). See (1955KH35, 1962SL03, 1965GA02).

38. ¹¹B(t, t)¹¹B

Angular distributions of elastically scattered tritons hasve been measured at E_t = 1.75 and 2.10 MeV. Optical model fits have been made (1968HE1N).

39. ¹¹B(³He, ⁶Li)⁸Be Q_m = 4.566

Angular distributions observed at E(³He) = 3.0 and 5.2 MeV suggest a cluster pick-up mechanism, indicating a substantial (⁸Be + t) configuration in ¹¹B (1967YO02).

40. ¹¹B(α, α)¹¹B

At E_α = 28.5 MeV, angular distributions are obtained for the elastic α-particles and the inelastic α's corresponding to ¹¹B*(2.12, 4.44, 5.02, 6.74 + 6.79, 7.30, 8.57) (1967NA06). See also (1964ST1K, 1966GE12).

41. (a) ¹¹B(¹¹B, ¹¹B)¹¹B
(b) ¹¹B(¹⁶O, ¹⁶O)¹¹B

For reaction (a), see (1967GU1A). For reaction (b) see (1966OE1A).

42. ¹¹C(β⁺)¹¹B Q_m = 1.981

See ¹¹C.

43. (a) ¹²C(γ, p)¹¹B Q_m = -15.957
(b) ¹²C(e, e'p)¹¹B Q_m = -15.957

For reaction (a) see (1962PA08, 1963WA18, 1965AL02, 1966PA05). For reaction (b) see (1962DO1A, 1962PA08, 1965AM1B, 1965CO1E). See also ¹²C.

44. ¹²C(p, 2p)¹¹B Q_m = -15.957

In the summed proton spectrum, gross structure is observed corresponding to Q = -15.6 ± 0.6 and -34.3 ± 0.8 MeV corresponding to ¹¹B_g.s. and an excited state with J^π = 1/2⁺ at E_x = 18.3 MeV (ejection of p- and s-protons, respectively) (1965RI1A, 1966TY01). See also (1958MA1B, 1958TY49, 1960GO1M, 1961PU1A, 1962GA09, 1962GA23, 1962GO1P, 1965BE1E, 1965CO1E, 1966BE1B, 1966WA12). A high resolution experiment shows groups corresponding to ¹¹B*(0, 2.12, 4.44, 5.02, 6.79) (1965PU02, 1967PU01). The angular correlation and energy distribution of the protons emitted at E_p = 45.5 MeV have been measured by (1967RI08) and compared with distorted-wave t-matrix approximation theory.

45. ¹²C(n, d)¹¹B Q_m = -13.732

See (1962AU1A, 1966ME03, 1967ME11).

46. ¹²C(d, ³He)¹¹B Q_m = -10.463

Angular distributions with DWBA indicate l = 1 pickup for ¹¹B*(0, 2.0, 4.8). No l = 3 fit is possible for the 5/2^- and 7/2^- states [¹¹B*(4.3, 6.5)], suggesting a double process involving ¹²C (2⁺) as an intermediate stage (1966CH1K). The ground-state angular distribution has also been determined at E_d = 82 MeV (1967AR21). At E_d = 28.5 MeV, the cross sections for the (d, ³He) and (d, t) reactions to the mirror ground states ¹¹B and ¹¹C are the same (1966DE1C). See also (1965PE17, 1967FI1G).

47. ¹²C(t, α)¹¹B Q_m = 3.858

Angular distirbutions of the α-particles to the ground and first excited states of ¹¹B have been measured at E_t = 1 to 2 MeV (1962GU01), 10.1 MeV (1962PU01) and 13 MeV (1965AJ01). At the two higher energies, the angular distributions of the α-particles to the 4.44 and 5.02 MeV states have also been determined. Ground state angular distributions have been measured at 18 energies between E_t = 1.5 and 3.2 MeV (1966SE1D, 1968SE1F). See also (1960MU07, 1961HO1F, 1962NE1D, 1963NI04, 1964BE1K, 1965HO1C, 1965NE1B).

48. ¹²C(¹²C, ¹³N)¹¹B Q_m = -14.013

See (1967VO1D, 1967WI04).

49. ¹²C(¹⁴N, ¹⁵O)¹¹B Q_m = -8.664

See (1966PO1B, 1967BI06).

50. ¹³C(n, t)¹¹B Q_m = -12.422

This reaction has not been reported.

51. ¹³C(p, ³He)¹¹B Q_m = -13.185

At E_p = 43.7 MeV, ³He particles are observed corresponding to a T = 3/2 state in ¹¹B: E_x = 13.02 ± 0.08 MeV (Γ = 358 ± 60 keV); L = 0 (J = 1/2^-) (1966MA2N). See also ¹¹C.

52. ¹³C(d, α)¹¹B Q_m = 5.168

Angular distributions of ground-state α-particles have been determined at E_d = 3.3 to 4.2 MeV (1963MA24), 10 to 12 MeV (1967CU1A). Alpha groups corresponding to the states at 2.12, 4.44 and 6.79 MeV have been observed by (1951LI29, 1953SP1A). The γ-decay of the 4.44 (1955BE62, 1958RA13) and 5.02 MeV states (1963AL21) is also reported. See also (1959EL43, 1965NE10, 1966KL06, 1966KL1E, 1966KL1F) and ¹⁵N in (1970AJ04).

53. ¹⁴C(p, α)¹¹B Q_m = -0.784

Angular distributions of the α-particles to the first four states of ¹¹B have been determined at E_p = 18 MeV (1962BR34). See also (1967EL1D).

54. ¹⁴N(n, α)¹¹B Q_m = -0.157

See (1958DO63, 1959GA14, 1959HA13, 1963MO04, 1963SE08, 1964MO1D, 1966CS1B, 1966MA2M, 1967MO21) and ¹⁵N in (1970AJ04).