A=12B (1980AJ01)

The half-life of ¹²B is 20.20 ± 0.02 msec (1978AL01): see Table 12.2 (in PDF or PS) of (1968AJ02) for a summary of earlier values. The decay is complex. ¹²B decays to ¹²C*(0, 4.4, 7.7, 10.3): see Table 12.15 (in PDF or PS). The transitions to ¹²C*(0, 4.4) are allowed: hence the J^π of ¹²B_g.s. is 1⁺.

2. ⁶Li(⁷Li, p)¹²B Q_m = 8.337

At E(⁷Li) = 2 MeV eleven groups of protons are reported to known states of ¹²B (1959MO12). Angular distributions have been measured at E(⁶Li) = 3.5 to 5.95 MeV. The distributions are generally featureless: see (1975AJ02).

3. ⁷Li(⁷Li, d)¹²B Q_m = 3.311

Angular distributions have been measured at E(⁷Li) = 2.10 to 5.75 MeV (1969CA1A: d₀, d₁, d₂, d₃₊₄). The mean lifetimes of ¹²B*(0.95, 2.62) are 295 ± 37 fsec and < 48 fsec, respectively (1969TH01). For γ-decay results see (1975AJ02).

4. ⁹Be(t, n)¹¹B Q_m = 9.5586 E_b = 12.928

Thirteen resonances have been reported corresponding to 13.6 < E_x < 14.7 MeV: see Table 12.3 (in PDF or PS) in (1975AJ02). See also (1977MA1N) and ¹¹B.

5. (a) ⁹Be(t, p)¹¹Be Q_m = -1.167 E_b = 12.928
(b) ⁹Be(t, d)¹⁰Be Q_m = 0.5545
(c) ⁹Be(t, t)⁹Be
(d) ⁹Be(t, α)⁸Li Q_m = 2.926
(e) ⁹Be(t, ⁶He)⁶Li Q_m = -5.383

Yields of elastically scattered tritons have been measured for E_t = 0.60 to 2.1 MeV: see (1975AJ02). Differential cross sections and analyzing power for elastic tritons have been measured at E_t-bar = 15 and 17 MeV (1978SC02). The yield of α₀ and α₁ (reaction (d)) have been obtained for E_t = 0.52 to 1.70 MeV (1969NA04). There is no evidence of the resonance structure reported in reaction 4. The analyzing powers of the reactions leading to ⁶He_g.s. and ⁶Li*(0, 3.56) have been measured at E_t-bar = 17 MeV (1979FL03). See also ⁶He, ⁶Li, ⁸Li and ⁹Be in (1979AJ01) and ¹¹Be here.

6. ⁹Be(α, p)¹²B Q_m = -6.886

See (1968AJ02).

7. ⁹Be(⁷Li, α)¹²B Q_m = 10.462

Observed α-particle groups are displayed in Table 12.3 (in PDF or PS). Angular distributions have been measured at E(⁷Li) = 3.3 to 6.2 MeV, at 30.3 MeV [see (1975AJ02)] and at 20 MeV (1975AJ03). Angular distributions to the first seven states are rather featureless and have approximate symmetry about 90°. The integrated cross sections go as 2J_f + 1 consistent with a compound nucleus mechanism for the transitions populating the low-lying states of ¹²B. It is suggested that the sharp states of ¹²B at high excitation energies correspond to states of high angular momenta with cluster configurations (1975AJ03).

8. (a) ¹⁰Be(d, p)¹¹Be Q_m = -1.722 E_b = 12.374
(b) ¹⁰Be(d, α)⁸Li Q_m = 2.372

The cross sections for production of ⁸Li (reaction (b)) and of ¹¹Be (reaction (a)) have been measured for E_d = 0.67 to 3.0 MeV and 2.3 to 12 MeV: the yields for both reactions vary smoothly with energy. No resonances are observed (1970GO11, 1973GO09).

9. ¹⁰B(t, p)¹²B Q_m = 6.343

Observed excited states are displayed in Table 12.4 (in PDF or PS). Angular distributions have been studied at E_t = 10 (1964MI04) and 23 MeV (1978AJ02). See also (1977ST1N) and (1975AJ02).

10. ¹¹B(n, γ)¹²B Q_m = 3.370

The thermal neutron capture section is 5 ± 3 mb (1962IM01) [(1973MU14) adopt 5.5 ± 3.3 mb]. The capture cross section shows a resonance at E_n = 20.8 ± 0.5 keV (see also reaction 11) with Γ_γ = 0.025 ± 0.008 eV (1969MO10). In the range 140 to 2325 keV, resonances are observed at E_n = 0.43, 1.03, 1.28 and 1.78 MeV, with radiation widths of 0.3, 0.3, 0.2 and 0.9 eV, respectively ( ± 50%) (1962IM01). See also (1976GAYV).

11. ¹¹B(n, n)¹¹B E_b = 3.370

The thermal (bound) scattering cross section is 3.9 ± 0.2 b. The scattering amplitude (bound) is a = 6.1 ± 0.1 fm (1973MU14). Parameters of observed resonances in σ_tot are shown in Table 12.5 (in PDF or PS).

Comparison of ¹¹B + n and of data from ¹¹B(d, p) shows that the E_n = 20.8 keV resonance is d-wave and that ¹²B*(3.389) has J^π = 3^-. The neutron width [3.1 ± 0.6 eV] is about the Wigner limit. The 0.43 MeV resonance [¹²B*(3.76)] is formed by l = 1; γ²_S=1 = γ²_S=2; J^π = 2⁺.

The polarization and differential cross sections have been measured for 0.075 ≤ E_n ≤ 2.2 MeV by (1970LA21) as has σ_t for 0.3 ≤ E_n ≤ 2.05 MeV. A two-channel R-matrix analysis fits both σ(θ) and P(θ) assuming broad 2^- (l = 0) and 4^- (l = 2) states at E_x = 4.37 and 4.54 MeV [E_n = 1.09 and 1.28 MeV] in addition to the sharp state ¹²B*(4.31) fitted with J^π = 1^-. The analysis also confirms J^π = 1⁺ for ¹²B*(5.00) (1970LA21). Differential cross sections have also been measured for 2.2 < E_n < 4.5 MeV by (1973NE19) and for 4.0 to 8.0 MeV by (1977WHZZ, 1978WH1B). See also (1976LA1C, 1977WH1A).

Recent additional measurements (1978WH1B) and R-matrix analysis for 2.6 < E_n < 4.0 MeV confirm J^π = 1^- (l_n = 0, 2) for the ¹²B* state at E_x = 5.8 - 6.0 MeV, and give 1^- (l_n = 0, 2) for ¹²B*(6.9) instead of 1⁺ (1973NE19). In the region 7.5 < E_x < 8.5 MeV 1^- and 2^- states of l_n = 0, 2 are present (1977WHZZ, 1978WH1B) and (R. Lane, private communication). Assignments of states at higher energies are displayed in Table 12.5 (in PDF or PS) (1977WHZZ, 1978WH1B). See also (1975AJ02).

Total cross sections from E_n = 3.4 to 15.5 MeV (1961FO07) and from 1 to 14 MeV (1979AU07) have been studied: see Table 12.5 (in PDF or PS). There is no evidence of sharp structure in the range 9.7 < E_x < 17.3 MeV. Limitations of statistical accuracy exclude observation of J = 0 levels above E_n = 4 MeV, and of J = 1 levels above E_n = 12 MeV in this work (1961FO07). The σ_t for natural boron has been measured for E_n = 2.5 to 15 MeV (1971FO1P, 1971FO24). Other cross section measurements have been reported at E_n = 7.55 to 14.5 MeV [see (1975AJ02)] and 14.1 MeV (1974HY01). See also ¹¹B and (1976GAYV).

12. (a) ¹¹B(n, p)¹¹Be Q_m = -10.726 E_b = 3.370
(b) ¹¹B(n, d)¹⁰Be Q_m = -9.0041
(c) ¹¹B(n, t)⁹Be Q_m = -9.5586
(d) ¹¹B(n, α)⁸Li Q_m = -6.633

The cross section for reaction (a) has been measured for E_n = 14.7 to 16.9 MeV: see (1975AJ02). See also (1974BO1E). For reaction (b) see (1976SL2A). For reaction (c) see (1978QA01). See also (1973BI1B) and (1976SL2A). The cross section for reaction (d) has been measured in the range E_n = 12.6 to 20.0 MeV and at E_n = 25 and 38 MeV: see (1975AJ02). No resonances are observed. See also (1974BO1E, 1974CA1J, 1976SL2A) and (1976GAYV).

13. ¹¹B(d, p)¹²B Q_m = 1.145

Observed proton groups and γ-rays are displayed in Table 12.6 (in PDF or PS). The J^π assignments for ¹²B*(0.95, 1.67) are derived as follows [see (1968AJ02) for detailed listing of earlier references]: 0.95 MeV: l_n = 1 leads to J^π = 0⁺, 1⁺, or 3⁺. The γ-radiation is anisotropic and therefore J ≠ 0 (1963WA20, 1968CO14). τ_m is too short for pure E2 and hence J ≠ 3, which is confirmed by studies of the polarization of γ₁, most recently by (1968GO17: E_d = 0.5 to 5.5 MeV). The results are consistent with J^π = 1⁺ or 2⁺. The latter is fixed by γ - γ correlations in the cascade 1.67 → 0.95 → g.s. (1968CH05). The mixing ratio δ = -0.08 ± 0.06 (1968GO17). Γ_γ = 2.2 ± 0.25 meV (1968OL01). See also (1968GO18, 1974KA29); 1.67 MeV: l_n = 0 and therefore J^π = 1^- or 2^-. The state decays primarily to ¹²B_g.s.. Gamma-gamma correlations lead to J^π = 2^- (1968CH05). An assignment of 1^- to ¹²B*(2.62) is made in a similar manner.

(1971MO14) have analyzed existing ¹¹B(d, p)¹²B and ¹¹B + p reactions and have listed the properties of the first seven T = 1 states in ¹²B and ¹²C: see Table 12.12 (in PDF or PS). Neutron reduced widths γ²_{λ_n} for the first six excited states in ¹²B were calculated from spectroscopic factors and compared with 2γ²_{λ_p} for the corresponding ¹²C states. The agreement was quite good once new values for the partial widths of ¹²C*(16.11) [see (1974AN19)] became available (1971MO14). For the polarization of ¹²B_g.s. see (1977PO1B) and reaction 15.

The j mixing A_{ls_3/2}/A_{ls_1/2} = -0.11 ± 0.03 or -0.90 ± 0.06 for ¹²B_g.s. and +0.12 ± 0.02 for ¹²B*(0.95) (1976TA07). See also (1975HU1H, 1975MC1E, 1975MI1F, 1976MI1J, 1977KA1V), (1976HA1J), (1977SA25; theor.) and ¹³C in (1981AJ01).

14. ¹¹B(α, ³He)¹²C Q_m = -17.208

See (1979CHZP).

15. ¹²Be(β^-)¹²B Q_m = 11.708

See ¹²Be.

16. (a) ¹²C(γ, π⁺)¹²B Q_m = -152.936
(b) ¹²C(e, eπ⁺)¹²B Q_m = -152.936
(c) ¹²C(π^-, γ)¹²B Q_m = 126.197

π⁺ electroproduction has been studied at E_π ≈ 17 and 29 MeV to ¹²B*(0.95, 1.7, 2.6, 4.5) (1979PA06). See also (1979MI06) and reaction 39 in ¹²C. At E_e = 195 MeV, angular distributions are reported for the π⁺ to ¹²B_g.s. and to possibly unresolved excited states (1977SH14), including ¹²B*(4.5) (1979SH1R). For reaction (c) see (1979AL1M). See also (1975HU1D, 1978FU04, 1978FU09; theor.).

17. ¹²C(μ^-, ν)¹²B Q_m = 92.290

Observations of γ-transitions have led to the determination of the capture rates to ¹²B*(0, 0.95, 1.67, 2.62); those to ¹²B*(0.95, 1.67) are consistent with zero (1972MI15). The polarization of ¹²B_g.s., P_av = 0.452 ± 0.042 (1977PO1B). The longitudinal polarization, P_L = -0.83 ± 0.21 (1979TR05). These two values lead to a neutrino polarization h_ν = -0.89 ± 0.23 [left-handed] (1979TR05). See also (1976SU03, 1978KO31; theor.).

18. ¹²C(n, p)¹²B Q_m = -12.587

At E_n = 45 to 64 MeV strong excitation of ¹²B*(0, 4.3, 7.7) is reported (1977FI1B, 1977SU1C). See also (1975MC19, 1976KI1D), (1976SL2A) and ¹³C in (1981AJ01).

19. ¹²C(⁷Li, ⁷Be)¹²B Q_m = -14.231

At E(⁷Li) = 52 MeV the population of ¹²B*(0, 0.95, 1.71, 2.70, 2.87) and ⁷Be(0) [and in the case of ¹²B(0), of ⁷Be*(0.43)] is reported by (1973BA34).

20. ¹³C(γ, p)¹²B Q_m = -17.533

At E_bs = 15 to 44 MeV the cross section for transitions to ¹²B*(0.95) has been measured by (1975PA09). See also ¹³C in (1981AJ01) and (1977MA06; theor.).

21. ¹³C(d, ³He)¹²B Q_m = -12.040

Angular distributions have been measured for the transitions to ¹²B*(0, 0.95) at E_d = 24.1, 26.2 and 27.5 MeV (1977LI02), 28 MeV (1972BR27) and 52 MeV (1975MA41; also to ¹²B*(2.72, 3.76, 5.00)) and at E_d = 29 MeV (1979CO08). (1977LI02) find S = 1.1 ± 0.2 and 2.0 ± 0.5 for the spectroscopic factors to ¹²B*(0, 0.95). C²S = 1.09 [assuming 1p_3/2], 2.17, 0.14, 0.07, 0.22 [assuming 1p_1/2] for ¹²B*(0, 0.95, 2.72, 3.76, 5.00) (1975MA41). See also (1979CO08). For a discussion of analog states of ¹²B and ¹²C see reaction 73 in ¹²C and (1977LI02, 1979CO08). See also (1977RI08) and (1979CO08) in ¹⁵N (1981AJ01).

22. ¹⁴C(p, ³He)¹²B Q_m = -17.992

At E_p = 54 MeV, in addition to transitions to ¹²B*(0, 0.95, 5.61), the population of T = 2 states at E_x = 12.72 ± 0.07 and 14.82 ± 0.10 MeV is reported. The angular distribution of ³He ions to ¹²B*(12.72) is fitted by L = 0; that to ¹²B*(14.82) is rather featureless [its T = 2 character is assigned from the energies of the analog states]: both states have Γ_c.m. ≲ 200 keV (1976AS01). See also (1975AJ02), and reaction 80 in ¹²C.

23. ¹⁴C(d, α)¹²B Q_m = 0.361

See (1968AJ02).

24. ¹⁴N(¹²C, ¹⁴O)¹²B Q_m = -18.514

At E(¹⁴N) = 118 MeV the excitation of ¹²B*(0, 0.95) is reported (1974AN36). See also (1975NA11) in ¹⁴O.

25. (a) ¹⁵N(n, α)¹²B Q_m = -7.621
(b) ¹⁸O(¹¹B, ¹⁷O)¹²B Q_m = -4.675

See (1975AJ02).