
^{11}B (1968AJ02)(See Energy Level Diagrams for ^{11}B) 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).
Angular distributions of the protons to ^{11}B states below E_{x} = 9.3 MeV have been measured for E(^{6}Li) = 2.4 to 9.0 MeV (1966KI09). Gamma spectra have been studied at E(^{6}Li) = 2.6 MeV. Relative populations to ^{11}B levels are reported (1962BE24). See also (1960SH01, 1962BE16, 1963LE09).
Three resonances for capture radiation are reported at E_{α} = 401, 819 and
958 keV, corresponding to ^{11}B 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 groundstate transition requires J^{π} = 3/2^{±} or 5/2^{±}. Correlations in the cascades eliminate all but J^{π} = 5/2^{+}, formed by pwave. θ^{2}_{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 ^{9}Be(^{3}He, p)^{11}B. E_{x} = 9.19 MeV. Angular correlations in the cascade transitions require J^{π} = 7/2^{±}; the groundstate transition fixes J^{π} = 7/2^{+} formed by fwaves, θ^{2} = 0.04, with an M2/E3 amplitude of 0.9 and an E3 strength of 6 to 17 Weisskopf units. See, however, ^{9}Be(^{3}He, p)^{11}B. E_{x} = 8.93 MeV. The angular distribution of the groundstate transition yields J^{π} = 3/2^{+} or 5/2^{±}. Consideration of the transition strength favors 5/2^{}.
Observed resonances are listed in Table 11.5 (in PDF or PS). Comparison with ^{10}B(n, α)^{7}Li 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).
See ^{8}Be in (1966LA04).
Elastic scattering has been studied for E_{α} = 1.6 to 12 MeV by (1966CU02). The inelastic scattering, leading to ^{7}Li*(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 ^{10}B(d, p)^{11}B) 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 ^{9}Be(^{3}He, p)^{11}B 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 ^{9}Be(^{3}He, p)^{11}B. 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 ^{7}Li(α, n)^{10}B* (1966CU02).
The lifetimes of ^{11}B*(6.79, 7.30, 8.00) are less than 50 fsec (1967THZX). Gamma spectra indicate that all bound levels are populated at E(^{6}Li) = 2.6 MeV (1962BE24). Angular distributions are not symmetric about 90°; an αtransfer process is suggested (1961MO02). Angular distributions have also been obtained at E(^{7}Li) = 3.78 to 5.95 MeV for the deuterons to ^{11}B*(0, 2.12, 4.44, 5.02, 6.74 + 6.79, 7.30) (1967KI03), and at E(^{7}Li) = 3.3 MeV (^{11}B* = 0, 2.12, 4.44, 5.02) (1967GA06). See also (1966RO1E, 1966RO1F).
Tritongamma coincidence studies yield the following branching ratios: ^{11}B*(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 ^{11}B*(6.79, 7.30, 8.00) are less than 0.5 msec (1967THZX). See also (1961MO02, 1962BE24, 1966RO1E, 1966RO1F, 1967WY1B).
Radiative transitions have been observed to ^{11}B*(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 γrays: 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).
The cross section follows the Gamow function for E_{d} = 70 to 110 keV (1955RA14). The fast neutron and γray 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 ^{10}B (1957SH65; see however, (1959NE1A)). The polarization angular distributions of the neutrons to ^{10}B*(0, 0.72, 1.74, 2.15) have been measured at E_{d} = 1.57, 2.06 and 2.48 MeV (1967MI1F). See also ^{10}B in (1966LA04) and (1965BU10, 1967SC43).
(1952CA19) reports broad maxima in the 90° yield of the groundstate 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 γrays (from ^{10}Be*) in the range E_{d} = 1.0 to 5.6 MeV. No resonances are observed in the yield of 6 MeV γrays 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 αparticles (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 (α_{0}, α_{1}) and 9 to 12.4 MeV (α_{2}) (1966DO1A). See also ^{7}Li 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 threebody reaction [reaction (d)] does not appear to occur (1953GE01). For reaction (e) see (1955HE83). See also (1962WI15, 1965MA57).
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 ^{9}Be in (1966LA04).
See (1962SE1A).
Proton groups have been observed to 23 states of ^{11}B: see Table 11.8 (in PDF or PS) (1959HI69, 1963GR20, 1966BR18). Angular distributions of many of these protons groups have been observed at E(^{3}He) = 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 ^{11}B*(6.74, 7.30, 8.00) (1960HI08). The narrow level at E_{x} = 12.565 MeV does not appear in ^{10}B(d, p)^{11}B and may therefore have T = 3/2 (1963GR20: see, however, ^{7}Li(α, α)^{7}Li). See also (1959AJ76) and ^{12}C. Gammaray branching ratios and multipolarities for ^{11}B 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 ^{10}B(d, p)^{11}B. E_{x} = 9.19 MeV. Γ_{γ}/Γ = 0.1^{+0.2}_{0.05}. From ^{7}Li(α, γ)^{11}B, 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 groundstate 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 ^{7}Li(α, γ)^{11}B, J^{π} = 3/2^{+}, 5/2^{+}, 5/2^{}. The internal pair correlation excludes J^{π} = 3/2^{+}, 5/2^{+}, and confirms 5/2^{}. The groundstate 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 ^{11}B(e, e')^{11}B*. 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 ^{11}B*(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 ^{10}B(d, p)^{11}B. See ^{11}B(e, e')^{11}B*. E_{x} = 8.00 MeV. Transitions to ^{11}B_{g.s.} and (2.12) are predominantly E1; thus E_{x} = 8.00 MeV has even parity, and the odd parity of ^{11}B*(2.12) is confirmed. The transition to ^{11}B*(2.12) is not isotropic, so J^{π} = 3/2^{+}. Comparison of branching ratios with analogous case in ^{11}C 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 βdecay from ^{11}Be indicates J^{π} ≤ 7/2^{+}. The relatively strong γbranch to ^{11}B*(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 ^{7}Li(α, γ)^{11}B, 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 ^{11}B*(2.12) argues against J = 5/2, therefore J^{π}1/2^{} or 3/2^{} (1961DO03). Angular correlation studies indicate a P_{2}(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 ^{7}Li(α, γ)^{11}B). E_{x} = 2.12 MeV. The lifetime (4.6 fsec) demands dipole radiation. The E1 transition from ^{11}B*(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 ^{11}B are consistent with ascription to p^{7}; there is evidence that ^{11}B*(8.93) also belongs to p^{7}, while ^{11}B*(8.57) appears more likely to belong to a higher configuration. See also (1960EL1C, 1961EL1A, 1962WE1C, 1963VA16, 1966WA1C).
At E_{α} = 28.3 MeV, differential cross sections have been measured (θ = 15° to 47°) for the deuteron groups to ^{11}B*(0, 2.12, 4.44, 5.02) (1965KA14). See also (1955RA41, 1962WE1C, 1967ZE1A).
Angular distributions and total cross sections have been determined for seven αgroups. In the range E(^{6}Li) = 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).
For reaction (a) see (1964CA18). For reaction (b) see (1964BO1M).
The thermal neutron capture cross section is 0.5 ± 0.2 b. The direct groundstate decay has Γ_{γ} = 0.01 eV (1957BA18). See also (1959AJ76).
The thermal scattering cross section (bound) for B is 4.4 ± 0.2 bn (1958HU18). The coherent scattering amplitude (bound) for ^{10}B 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 swaves 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 αchannel (1967LA1N). See also (1959MA1C, 1960AN14, 1966AG1A, 1967CI1B) and (1959AJ76).
The yield of 0.7 MeV γrays 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).
The thermal cross section is < 0.2 b (1958HU18); the cross section for fast pile neutrons is 3 mb (1948EG1A).
See (1954RI15). See also (1963GO1M).
The ^{10}B(n, t)^{4}He^{4}He 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 ^{10}B(n, α) reaction: see Table 11.10 (in PDF or PS). See also (1964ST25, 1966JE1B).
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 groundstate to excited state transitions varies monotonically with energy although the 0.53 MeV resonance appears to influence the crosssection 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).
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 ^{11}B*(2.12) which appears to involve a spinflip 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 p^{7} levels (a/K ≈ 4.0) (1956KU1A, 1960BI08, 1965OL03). There is some disagreement about the parities of ^{11}B*(8.57, 8.93): see ^{9}Be(^{3}He, p)^{11}B 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 ^{10}B (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 ^{9}Be(^{3}He, p)^{11}B is not seen. This suggests T = 1/2 and 3/2, respectively, for these two states. See, however, ^{7}Li(α, α)^{7}Li. See also (1959BO1C, 1959BU1F, 1959HO1D, 1959LE1B, 1959TO1A, 1960BI1B, 1960NE1C, 1961BU16, 1961TE02, 1961ZE03, 1962ME1B, 1963GL1C, 1963MO1E, 1963SM05, 1963TA1A, 1963TA1C, 1964MA57, 1965BA31, 1965ST1E, 1966BA1X, 1966BA2R, 1967SC1K) and ^{12}C. Polarization studies are reported by (1958HE47, 1959HI1E, 1960ER1A, 1960TA27, 1961ZI02, 1962PA12, 1962TA13, 1962ZI01, 1963BO1J, 1963ER1A, 1964BE08, 1964PA1E, 1965SZ01, 1965ZI1A, 1966BA2V).
At E_{d} = 5.5 MeV, deuteron groups are observed to the ground state of ^{11}B 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 ^{13}C in (1970AJ04).
Not reported.
See (1963TO1D, 1963TO1E, 1966CO27, 1966GA04, 1967CO1T).
The decay properties of ^{11}Be 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 ^{11}Be (1961DO03, 1964AL22).
Mean gamma widths of lowlying 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 ^{11}B*(9.19): see, however, ^{7}Li(α, γ)^{11}B. 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).
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).
See (1961DO08, 1962CH26, 1962LI13, 1962VO1C, 1963KI1C) for reaction (a), and (1962CH26, 1962VO1C, 1963BA1K) for reaction (b).
See (1955AJ61, 1959AJ76, 1962VO1C).
The chargescattering 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 fm^{2}, suggests a jj coupling scheme for ^{11}B_{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). Groundstate 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 ^{11}B*(8.57), the dependence of the transition probability on q^{2} indicates an E2M1 mixture: hence the parity is odd, J ≤ 5/2. The observed γwidth if ^{11}B*(8.93) implies Γ_{α} = 0.03 eV (compare ^{9}Be(^{3}He, p)^{11}B (1966SP02)). See also (1962BA1D, 1964BR1N, 1966RI1G, 1967KA1A, 1967LE1E).
See (1955GR18, 1961LI04, 1962TE05, 1963OP1A, 1966FR18).
Study of the pair line spectrum of the 2.12 MeV γray 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 γray (1957MC35): it exhibits < 2.0 × 10^{3} part of circular polarization; this observation places an upper limit of F^{2} ≲ 1 × 10^{7} for the intensity of the parity nonconserving part of the wave function (1958WI41). At E_{p} = 185 MeV, proton groups are observed to ^{11}B levels at 2.2 ± 0.1, 4.5 ± 0.1, 5.1 ± 0.15, 6.8 ± 0.1 (probably corresponds to ^{11}B*(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 ^{11}B*(4.44) and 90 ± 40 meV, for ^{11}B*(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 ^{10}Be in (1966LA04).
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).
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).
Angular distributions observed at E(^{3}He) = 3.0 and 5.2 MeV suggest a cluster pickup mechanism, indicating a substantial (^{8}Be + t) configuration in ^{11}B (1967YO02).
At E_{α} = 28.5 MeV, angular distributions are obtained for the elastic αparticles and the inelastic α's corresponding to ^{11}B*(2.12, 4.44, 5.02, 6.74 + 6.79, 7.30, 8.57) (1967NA06). See also (1964ST1K, 1966GE12).
For reaction (a), see (1967GU1A). For reaction (b) see (1966OE1A).
See ^{11}C.
For reaction (a) see (1962PA08, 1963WA18, 1965AL02, 1966PA05). For reaction (b) see (1962DO1A, 1962PA08, 1965AM1B, 1965CO1E). See also ^{12}C.
In the summed proton spectrum, gross structure is observed corresponding to Q = 15.6 ± 0.6 and 34.3 ± 0.8 MeV corresponding to ^{11}B_{g.s.} and an excited state with J^{π} = 1/2^{+} at E_{x} = 18.3 MeV (ejection of p and sprotons, respectively) (1965RI1A, 1966TY01). See also (1958MA1B, 1958TY49, 1960GO1M, 1961PU1A, 1962GA09, 1962GA23, 1962GO1P, 1965BE1E, 1965CO1E, 1966BE1B, 1966WA12). A high resolution experiment shows groups corresponding to ^{11}B*(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 distortedwave tmatrix approximation theory. See also (1960GO16, 1961CL09, 1961GA14, 1962CO17, 1962VA1G, 1963CL1B, 1963GR1G, 1963RI1B, 1964BO1L, 1966YU1A, 1967YU02; expt.) and (1960RI1B, 1962BA1J, 1962CL13, 1962DI1A, 1962IN1A, 1963BE42, 1963CL07, 1963YU1A, 1964BA1C, 1965YU1B, 1966LI1E, 1966NG1B, 1967JA1E; theor.).
See (1962AU1A, 1966ME03, 1967ME11).
Angular distributions with DWBA indicate l = 1 pickup for ^{11}B*(0, 2.0, 4.8). No l = 3 fit is possible for the 5/2^{} and 7/2^{} states [^{11}B*(4.3, 6.5)], suggesting a double process involving ^{12}C (2^{+}) as an intermediate stage (1966CH1K). The groundstate angular distribution has also been determined at E_{d} = 82 MeV (1967AR21). At E_{d} = 28.5 MeV, the cross sections for the (d, ^{3}He) and (d, t) reactions to the mirror ground states ^{11}B and ^{11}C are the same (1966DE1C). See also (1965PE17, 1967FI1G).
Angular distirbutions of the αparticles to the ground and first excited states of ^{11}B 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 αparticles 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).
This reaction has not been reported.
At E_{p} = 43.7 MeV, ^{3}He particles are observed corresponding to a T = 3/2 state in ^{11}B: E_{x} = 13.02 ± 0.08 MeV (Γ = 358 ± 60 keV); L = 0 (J = 1/2^{}) (1966MA2N). See also ^{11}C.
Angular distributions of groundstate αparticles 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 γdecay of the 4.44 (1955BE62, 1958RA13) and 5.02 MeV states (1963AL21) is also reported. See also (1959EL43, 1965NE10, 1966KL06, 1966KL1E, 1966KL1F) and ^{15}N in (1970AJ04).
Angular distributions of the αparticles to the first four states of ^{11}B have been determined at E_{p} = 18 MeV (1962BR34). See also (1967EL1D).
See (1958DO63, 1959GA14, 1959HA13, 1963MO04, 1963SE08, 1964MO1D, 1966CS1B, 1966MA2M, 1967MO21) and ^{15}N in (1970AJ04).
