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GENERAL: See also Table 11.1 [Table of Energy Levels] (in PDF or PS).

Theory: See (1956KU1A, 1957KU58, 1958FR1C).

1. 7Li(α, γ)11B

Qm = 8.670

Three resonances are reported below E_α = 2.5 MeV (1951BE13, 1954HE22): see Table 11.2 (in PDF or PS). Study of α-γ and γ-γ angular correlations, taken together with the relative γ-intensities, leads to the following assignments: 9.28 MeV level, J = 5/2⁺; 9.19 MeV, J = 5/2^-; 8.93 MeV, J = 3/2 or 5/2; 6.81 MeV, J = 3/2^-; 4.46 MeV, J = 5/2^- ((1952JO1B) and D.H. Wilkinson, private communication). The strength of the transition (8.92 → g.s.) implies E1 radiation (1958BI31). Angular distributions of several gamma rays at each resonance are tabulated by (1957ME1D); no terms higher than cos²θ are indicated. The absence of the transition (9.28 → 2.14) speaks for J = 1/2^- for the latter (1957WI26). Angular distributions of γ-rays from the 9.28 MeV level have been measured by (1958FE70). The results are in agreement with assignments J = 5/2⁺ and 5/2^- for ¹¹B*(9.28, 4.46), respectively. The angular distribution of the transition 9.28 → 6.76 strongly favors J = 7/2^- for the latter. See also (1958ME77): ¹¹B(γ, α)⁷Li, and ¹⁰B(d, p)¹¹B.

2. 7Li(α, n)10B

Qm = -2.793

Eb = 8.670

For E_α < 5.8 MeV, two resonances are observed; at E_α = 4.7 MeV (broad), and 5.15 ± 0.08 MeV (Γ = 0.22 MeV) corresponding to ¹¹B*(11.68 ± 0.10, 11.95 ± 0.08) (1957BI84). A further resonance at E_α = 7.15 MeV, ¹¹B*(13.22), is reported by (1958MA1J, 1959GI47). Calculation of σ(¹⁰B(n, α)⁷Li) from the observed yield of ⁷Li(α, n)¹⁰B gives good agreement for E_n = 0 to 0.8 MeV. The 5.15 MeV resonance corresponds to that reported in σ(n, α) at 0.52 MeV: E_x = 11.95 MeV. It is concluded that the resonance is formed by s or p-wave neutrons, J = 5/2⁺ or 3/2^-, Γ_n ≈ 20 keV and Γ_α ≈ 300 keV (1959GI47). See also (1950HO80).

3. 7Li(α, p)10Be

Qm = -2.566

Eb = 8.670

See (1937EC1A).

4. 7Li(α, α')7Li*

Eb = 8.670

Observed resonances in the yield of 0.48 MeV γ-radiation are exhibited in Table 11.3 (in PDF or PS) (1954HE22, 1954LI48, 1957BI84). Sum rule limits give J ≤ 5/2 for the 9.88 MeV level and J ≤ 7/2 for the 10.26 MeV level (1954LI48).

5. 9Be(d, γ)11B

Qm = 15.822

This reaction has not been observed: at E_d = 0.9 MeV, σ < 1.8 μb; at E_d = 1.5 MeV, σ < 20 μb (1955AL16).

6. 9Be(d, n)10B

Qm = 4.358

Eb = 15.822

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 broad resonance at E_d = 1 MeV (1949EV1A, 1955BO1A, 1957SH65). 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. Angular distributions change markedly through the resonance except for that corresponding to ¹⁰B*(3.58), which is dominated by stripping throughout (1957SH65). On the other hand, (1958NE38, 1959NE1A) have obtained integrated cross sections for three separate neutron groups from E_d = 0.5 to 2.0 MeV and find no evidence of a resonance near 1 MeV. See also ¹⁰B.

7. 9Be(d, d)9Be

Eb = 15.822

In the range E_d = 1.02 to 1.44 MeV, two resonance anomalies are reported by (1956JU17) at E_d = 1.162 and 1.348 MeV corresponding to ¹¹B*(16.77, 16.93) (Γ ≈ 70 and 120 keV, respectively). See also ⁹Be.

8. (a) 9Be(d, p)10Be	Qm = 4.585	Eb = 15.822
(b) 9Be(d, α)7Li	Qm = 7.152
(c) 9Be(d, t)8Be	Qm = 4.592
(d) 9Be(d, 2α)3H	Qm = 4.686
(e) 9Be(d, tn)7Be	Qm = -14.307

Reaction (a) exhibits a simple Gamow dependence to 250 keV (1953SA1A). Angular distributions for E_d < 1.5 MeV are reported by (1952DE24, 1955JU10, 1955JU1B, 1957HY1A, 1957SM78, 1958JU38). The distributions of long-range protons for E_d = 0.1 to 0.2 MeV are analyzed in terms of two ¹¹B states with J = 1/2^- and 1/2⁺ or J = 3/2^- and 1/2⁺ (1957SM78). (1952CA19) reports broad maxima in the 90° yield of ground-state protons at E_d ≈ 0.9, (1.3) and 2.1 MeV. (1957MC35) observe broad resonances at 1.3 and possibly at 1.8 MeV in the yield of 3.37 MeV γ-rays, 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 cross section for production of ¹⁰Be (reaction (a)) rises to a peak value of ≈ 0.34 b at ≈ 4 MeV and then falls almost linearly to ≈ 0.08 b at ≈ 21.5 MeV (1955HE83). See also (1957CO54).

The cross section for reaction (b) shows a simple Gamow rise to E_d = 250 keV (1953SA1A). Angular distributions have been measured for E_d = 0.3 to 0.7 MeV by (1951RE01): see also ⁷Li. 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), and at several energies in the range E_d = 3 to 19 MeV by (1955HE83). The forward yield of tritons shows a peak at E_d = 1.38 MeV (1955JU10, 1955JU1B). There seems also the possibility of a resonance at E_d = 0.87 MeV (1958JU38). Triton angular distributions for E_d = 0.1 to 0.2 MeV are analyzed in terms of two ¹¹B states with J = 5/2^- and 3/2⁺ (1957SM78). See also (1957HY1A) and ⁸Be.

Relative yields for the various groups from reactions (a), (b) and (c) are given by (1953GE01). See also (1957JA37).

The direct three-body reaction (d) does not appear to occur (1953GE01). The cross section for reaction (e) has been measured from threshold to E_d ≈ 21.5 MeV (σ ≈ 80 μb) (1955HE83).

9. 9Be(t, n)11B

Qm = 9.564

Not reported.

10. 9Be(3He, p)11B

Qm = 10.329

Angular distributions of the protons to the ground state and several excited states of ¹¹B have been determined at various bombarding energies from 2 to 6 MeV: see ¹²C. See also (1956HL01, 1956WO1A, 1957JO1B).

Gamma rays from the first nine excited states have been observed at E(³He) = 2.1 MeV in coincidence with proton groups. The direct ground state gamma-transition is observed for all the levels. In addition the cascade through the 2.14 MeV state is observed from the 5.03, 6.81, 7.99 and 8.57 MeV states and, possibly, from the 6.76 and 8.92 MeV states, generally with an intensity comparable with that of the corresponding ground state transition. The gamma-ray width, Γ_γ, of the 8.92 MeV level is found to be comparable with its Γ_α. The decay scheme derived from this work is shown in Fig. 17 (1957FE1B, 1958FE70). The branching of the 5.03 and 7.30 MeV levels agrees with the shell-model assignments 3/2^- and 5/2^- (1957KU58, 1958FE70). At E(³He) = 5.7 MeV, proton groups are reported to levels at 2.126 ± 0.010, 4.459 ± 0.010, 5.037 ± 0.010, 6.756 ± 0.010, 6.807 ± 0.010, 7.296 ± 0.010, 7.987 ± 0.010, 8.569 ± 0.010, 8.927 ± 0.010, 9.191 ± 0.010, 9.278 ± 0.010 and 9.87 ± 0.02 MeV. The 9.87 MeV state is broad, Γ ≈ 150 keV (S. Hinds and R. Middleton, private communication). See also (1954MO1E, 1958BR1D, 1958SW63) and ⁷Li(α, γ)¹¹B.

11. 9Be(α, d)11B

Qm = -8.022

Deuteron groups have been observed at E_α = 21.6 MeV to the ground and 2.14 MeV states of ¹¹B. A search in the region E_x = 0.4 to 1.0 MeV showed no deuteron groups with intensity greater than 0.1 of the intensity of the two observed groups (1955RA41).

12. 10B(n, γ)11B

Qm = 11.464

The thermal neutron capture cross section is 0.5 ± 0.2 b. Observed capture γ-rays are listed in Table 11.4 (in PDF or PS). The relative weakness of the ground state transition suggests J = 7/2⁺ for the capturing level.

13. 10B(n, n)10B

Eb = 11.464

The epithermal scattering cross section (free) is 3.6 ± 0.2 b (1958HU18). Broad maxima appear in the total cross section at E_n = 1.9 and 2.8 MeV (1951BO45) and at 4 MeV (1957HU1D); additional peaks near 0.2 and 0.4 MeV may be indicated (1951BO45). Differential cross sections have been measured at E_n = 0.55, 1.00 and 1.50 MeV: derived phase shifts are δ₀ = -53.5° at E_n = 0.55 MeV, δ₀ = -60.7°, δ₁ = -4.0° at E_n = 1.00 MeV, and δ₀ = -66.9°, δ₁ = -10.3°, δ₂ = -2.9° at E_n = 1.50 MeV (1955WI25). The total cross section decreases from ≈ 1.9 b at 4.4 MeV to 1.6 b at 5.6 MeV and then remains approximately constant at ≈ 1.5 b from 6 to 9.7 MeV (1954NE1A, 1956BE98). At E_n = 14 MeV it is 1.47 ± 0.03 b (1952CO41) and it remains nearly constant to 18 MeV (1954CO16: σ = 1.45 ± 0.02 b). See (1957HU1D).

14. 10B(n, n')10B*

Eb = 11.456

See (1952PH01) and (1956DA23).

15. 10B(n, p)10Be

Qm = 0.227

Eb = 11.464

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

16. 10B(n, d)9Be

Qm = -4.358

Eb = 11.464

At E_n = 14 MeV, the integrated cross sections (0° to 90°, c.m.) for the transitions to the ground and the 2.4 MeV states of ⁹Be are 21 ± 3 mb and 16 ± 2 mb, respectively (1954RI15). See also (1956FR18).

17. 10B(n, t)8Be

Qm = 0.234

Eb = 11.464

For E_n = 5.20 MeV, production of tritons appears to be mainly via ¹⁰B(n, α)⁷Li*(4.7) and direct three-body breakup (1956FR18). Cross sections at E_n = 4, 5.6, 9.6 and 14.1 MeV are 95 ± 10, 230 ± 25, 125 ± 15 and 85 ± 6 mb, respectively (1958WY67).

18. 10B(n, α)7Li

Qm = 2.793

Eb = 11.464

Recent values for the thermal neutron absorption cross section in natural boron are 749 ± 4 b (1953CA45), 755 ± 3 b (1953HA1C), 744 ± 20 b (1954SC87), 764 ± 3 b (1954VO1A) and 760 ± 3 b (1956CO1E). (1958HU18) give 755 ± 2 b for the thermal absorption cross section in "U. S. standard" boron and 3813 b for the thermal isotropic cross section; see also (1957HU1D). The cross section follows the 1/v law from 7 × 10^-4 eV to 100 keV (1955HU1B, 1957BI84). (1957BI1F) report σ_total = 642/√E_n + 2.45 b for E_n = 3 to 70 keV. The data from E_n = 0 to 250 keV can be satisfactorily interpreted in terms of the ¹¹B levels at 11.46 and 11.68 MeV (E_n = 0 and 140 keV) observed in ⁷Li(α, α')⁷Li* (1957BI84). (1957BE71) find, on the other hand, that deviations from the 1/v law for E_n < 1 MeV indicate a single broad level at E_n ≈ 250 keV with J = 5/2⁺ or 7/2⁺, Γ_α ≈ 400 keV, Γ_n ≈ 200 keV. A pronounced resonance is observed at E_n = 1.86 MeV: Γ_c.m. = 0.45 MeV ((1957BI84) and (1951PE18); see also (1950ST1A) and (1952BI1A)). There are indications of less pronounced resonances at 0.53, 2.8 and 4.1 MeV (with Γ_c.m. = 0.10, 0.3 and 0.5 MeV) in the energy range to E_n = 4.8 MeV (1957BI84). The ratio of ground state to excited state transition varies strongly with energy: see (1952AJ38, 1954DE38, 1958BU02).

Cross sections for production of 2α + t either through the 4.6 MeV level of ⁷Li or via three-body breakup have been determined for E_n = 4 to 19.5 MeV. A strong maximum near E_n = 5.6 MeV may indicate a resonance near ¹¹B*(16.6) (1956FR18, 1958WY66). See also (1955AJ61).

19. 10B(d, p)11B

Qm = 9.237

Proton groups reported by (1951VA1A) and (1953EL12) are listed in Table 11.5 (in PDF or PS). No other levels are observed below E_x = 11.46 MeV: the known levels observed in ⁷Li(α, α')⁷Li are presumably too wide to be seen here. See also (1954KH1A, 1955KH35).

The angular distribution of protons leading to the ground state (J = 3/2^-) shows a well-developed l_n = 1 stripping pattern at all energies ≳ 2.0 MeV (1954EV1A, 1958EV01: 7.7 MeV), (1953HO48: 8 MeV), (1956ZE1A: 10 MeV), (1957LE1F: 15.1 MeV), (1956MA69: 1.0 to 3.0 MeV); see, however, (1957CO54). Even below E_d = 1 MeV, stripping appears to play an important role in formation of this level (1954BU06, 1954PA28, 1957HA1H). The relatively large neutron capture probability suggests a single-particle character (1953HO48, 1954EV1A). See also (1957CO54, 1957HA1H). The polarization has been studied by (1958HE47, 1958HI74).

For the 2.1 MeV state, the evidence is not so clear: the pattern though generally of an l_n = 1 shape (see, however, (1954PA28, 1957LE1F)) shows strong variations with energy (1954EV1A, 1956MA69, 1956ZE1A, 1957CO54, 1957LE1F, 1958EV01). An l_n = 1 formation implies 3/2^- ≤ J ≤ 9/2^-, in contradiction to the shell-model expectation that the state should have J = 1/2^-; however to form such a state requires l_n = 3, involving rearrangement of several nucleons and hence a low probability (1956MA69, 1958EV01). The more probable mode of formation would appear to involve a nucleon exchange (1958EV01) or a spin reversal of the outgoing proton (1957WI26). The observation that the polarization of protons for this state is opposite to those corresponding to the ground state is consistent with either point of view, and permits 1/2^- ≤ J ≤ 11/2^- (1958HE47). Support for the assignment J = 1/2 is found in the observed isotropy of the p-γ correlation (see below): see also ¹¹B(p, p')¹¹B* and (1957WI26, 1958BO1C).

The 4.46, 5.03 and 6.76 MeV states are also formed by l_n = 1. The large neutron capture probability for the 6.76 MeV state indicates that it has a single-particle character (1954EV1A, 1958BI31). See also (1957CO54, 1957SJ1C). The next four states appear only weakly and probably arise from configuration mixing (1958BI31).

For the 8.92 MeV state, l_n = 2 with a small admixture of l_n = 0 is indicated; J = 5/2⁺, 7/2⁺. The large γ-width suggests J = 5/2⁺. The 9.19 and 9.28 MeV state are formed with l_n = 0, J = 5/2⁺ or 7/2⁺; the intensity ratio is consistent with J(9.19) = 7/2⁺, J(9.28) = 5/2⁺. Again, the high relative intensities suggest that these three are single-particle states, formed by direct capture into the 1d, 2s, shell (1958BI31); see also ⁷Li(α, γ)¹¹B.

Gamma rays reported by (1955BE81) and (1955SA1B) are listed in Table 11.6 (in PDF or PS). The p-γ angular correlation through the 2.14 MeV state is isotropic to ≈ 4%, consistent with J = 1/2: see (1953TH1B, 1955GO1D, 1956GO1L, 1956GO1M, 1956GO39, 1957GA1B). The angular correlation through 4.46 MeV state is consistent with J = 3/2^- or 5/2^-; that through the 6.76 MeV state rules out J = 3/2 and suggest J = 9/2 is unlikely for that state (1957CO54). See also (1956VA17).

20. 10B(t, d)11B

Qm = 5.205

Not reported.

21. 10B(α, 3He)11B

Qm = -9.114

Not reported.

22. 11Be(β-)11B

Qm = 11.48

The decay properties of ¹¹Be are exhibited in Table 11.7 (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 transition probabilities to ¹¹B_g.s., J = 3/2^-, and ¹¹B*(2.1), J = 1/2^-, suggest J = 1/2^- for ¹¹Be, but it is not clear why the transition should be so much inhibited as compared with other allowed transitions (1959WI49).

23. 11B(γ, γ)11B

The mean life of the 4.46 MeV level, determined by resonance absorption and scattering is τ_m = 1.17 ± 0.17 × 10^-15 sec, assuming J = 5/2. On the same assumption, the intensity ratio of quadrupole to dipole transitions is ≤ 0.2 (1958RA14). A mean life of ≈ 1.5 × 10^-15 sec is calculated by (1957KU58).

A similar experiment yields τ_m = (4.6 ± 0.6) × 10^-15 sec for the 2.1 MeV state, assuming J = 1/2. The result does not distinguish J = 1/2^- from J = 1/2⁺, but the shortness of the lifetime excludes J > 1/2 (1958ME79): see (1957WI26: ¹¹B(p, p')¹¹B*). A calculation in intermediate coupling, assuming an M1 transition yields τ_m = (2.5 to 5) × 10^-15 sec (1957KU58). See also (1958MC1D).

24. 11B(γ, n)10B

Qm = -11.464

See (1951SH63) and (1955TI1A).

25. 11B(γ, t)4He + 4He

Qm = -11.136

See (1955AJ61).

26. 11B(γ, α)7Li

Qm = -8.670

Resonance absorption of 9.19 MeV radiation yields Γ < 100 eV, (2J + 1)Γ_γ ≈ 0.8 eV for ¹¹B*(9.19) (1958ME77).

27. 11B(n, n')11B*

At E_n = 4.5 MeV, a 2.2 MeV γ-ray is reported (1955GR18, 1956DA01). See also (1954SC85).

28. 11B(p, p')11B*

At E_p = 3.58 MeV, a 2.134 ± 0.005 MeV γ-ray is observed (1957MC35); see also (1953HU29). The mean lifetime of the 2.14 MeV state has been determined by a Doppler shift measurement to be < 4 × 10^-14 sec (1957WI26): see ¹¹B(γ, γ)¹¹B. It is pointed out that the observed isotropy in ¹⁰B(d, pγ)¹¹B requires a nearly pure E2 transition if J = 3/2^- and the present lifetime value excludes E2. On the other hand, the lifetime is quite consistent with M1 (1957WI26). The 2.14 MeV γ-ray 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, inelastic groups with Q = -4.7, -6.6 and -8.5 MeV are observed; the latter shows strong forward peaking and is attributed to a spin flip of a target nucleon, indicating J = 1/2^-, 3/2^- or 5/2^- (1958TY46). See also (1955AJ61, 1956ST1D) and ¹²C.

29. 11B(d, d')11B*

Ground state deuterons have been observed at E_d = 4.2 MeV (1955KH35).

30. 11C(β+)11B

Qm = 1.981

See ¹¹C.

31. 12C(γ, p)11B

Qm = -15.958

See ¹²C.

32. 12C(p, 2p)11B

Qm = -15.958

At E_p = 185 MeV, the summed proton spectrum shows peaks attributed to removal of p- and s-protons (1958MA1B, 1958TY47).

33. (a) 12C(n, d)11B	Qm = -13.731
(b) 12C(d, 3He)11B	Qm = -10.465

Not reported.

34. 12C(t, α)11B

Qm = 3.855

This reaction has been observed at E_t = 1.4 MeV (1955CU17). See also (1958JA06).

35. (a) 13C(n, t)11B	Qm = -12.419
(b) 13C(p, 3He)11B	Qm = -13.184

Not reported.

36. 13C(d, α)11B

Qm = 5.167

Alpha-particle groups have been observed corresponding to ¹¹B*(2.107 ± 0.017) (1951LI29) and ¹¹B*(4.45, 6.83) (1953SP1A). A 4.46 MeV γ-ray observed by (1955BE62) in (¹³C + d) is definitely assigned to the present reaction by (1958RA13). See also (1955AJ61).

37. 14C(p, α)11B

Qm = -0.780

Not reported.

38. 14N(n, α)11B

Qm = -0.152

Q₀-values of -0.12 ± 0.06 and -0.18 ± 0.05 MeV are reported by (1958DO63). See also (1952LI24).