A=12B (1975AJ02)

The half-life of ¹²B is 20.41 ± 0.06 msec: see Table 12.2 (in PDF or PS) here and Tables 12.1 (in PDF or PS) and 12.2 (in PDF or PS) in (1968AJ02). The decay is complex; ¹²B decays to ¹²C*(0, 4.4, 7.7, 10.3): see Table 12.16 (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 MeV (1967GA06: p₀ → p₃) and E(⁷Li) = 3.78 to 5.95 MeV (1967KI03: p₀, p₁, p₂, p₃₊₄, p₅). Except for p₂ the distributions are nearly isotropic. See also (1968AJ02).

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 gamma decay of the first four excited states has been studied by (1963CA09): ¹²B*(0.95) decays of course to the ground state. So, primarily, do ¹²B*(1.67) [> 98%] and ¹²B*(2.72) [> 80%], while ¹²B*(2.62) decays [> 90%] via ¹²B*(0.95, 1.67). [See also Table 12.7 (in PDF or PS).] The mean lifetimes of ¹²B*(0.95, 2.62) are 295 ± 37 fsec and < 48 fsec, respectively (1969TH01). See also (1967CA1D, 1974CE06).

4. ⁹Be(t, n)¹¹B Q_m = 9.5591 E_b = 12.928

Reported resonances in the yield of neutrons at θ = 0° are listed in Table 12.3 (in PDF or PS) (1961VA1C). See also ¹¹B.

5. (a) ⁹Be(t, d)¹⁰Be Q_m = 0.5544 E_b = 12.928
(b) ⁹Be(t, t)⁹Be
(c) ⁹Be(t, α)⁸Li Q_m = 2.926

Yields of elastically scattered tritons have been measured for E_t = 0.60 to 1.70 MeV (1969NA04) and 1.0 to 2.1 MeV (1970CO04). The yields of α-particles [α₀, α₁] have been obtained for E_t = 0.52 to 1.70 MeV by (1969NA04). See also (1970CO04). There is no evidence of the resonance structure observed in reaction 4. See also ⁸Li and ⁹Be in (1974AJ01). For reaction (a) see (1969NA04) and ¹⁰Be in (1974AJ01).

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 12.4 (in PDF or PS) (1961HO19, 1969GL07, 1971AJ1B). Angular distributions have been measured at E(⁷Li) = 3.3, 3.5, 3.75 MeV (1961HO19: α₀ → α₄), 5.6 to 6.2 MeV (1969SN02: α₀ → α₄) and 30.3 MeV (1969GL07: to most states listed in Table 12.3 (in PDF or PS)). See also (1970OG1A).

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

Excited states of ¹²B observed by (1960JA17) at E_t = 5.5 MeV and by (1964MI04) at E_t = 10 MeV are displayed in Table 12.5 (in PDF or PS). See also (1968CO1H), (1967OG1A) and (1969SO02, 1970BA58, 1970KA38, 1970MA04, 1970MA38, 1970NE1F, 1974GU1D; theor.).

10. ¹¹B(n, γ)¹²B Q_m = 3.369

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). For astrophysical implications see (1968FOZY).

11. ¹¹B(n, n)¹¹B E_b = 3.369

The thermal (bound) scattering cross section is 3.9 ± 0.2 b. The scattering amplitude (bound) is a = 6.1 ± 0.1 fm (1973MU14). See also (1969BA1P). Parameters of observed resonances in σ_tot are shown in Table 12.6 (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*(3.388) has J^π = 3^-. The neutron width [3.1 ± 0.6 eV] is about the Wigner limit (1969MO10). The 0.43 MeV resonance [¹²B*(3.76)] is formed by l = 1; γ²_S=1 = γ²_S=2; J^π = 2⁺ (1955WI25, 1962EL01, 1970LA21).

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*(4.30) fitted with J^π = 1^-. The analysis also confirms J^π = 1⁺ for ¹²B*(4.99) (1970LA21). Differential cross sections have also been measured for 2.2 < E_n < 4.5 MeV by (1973NE1F, 1973NE19) and analyzed by a three-level R-matrix calculation. The fit is quite good if assignments 1^- and (1⁺) are made for broad states of ¹²B at E_x = 5.8 and 6.8 MeV, respectively [E_n = 2.7 and 3.8 MeV]. ¹²B*(5.61, 5.73, 6.6) are assigned J^π = 3⁺, 3^- and (1⁺), respectively (1973NE19). See also (1974BI07; theor.). For a study of the excitation function of ¹¹B(n, n'γ₁) see (1961LI04).

Total cross sections from E_n = 3.4 to 15.5 MeV have been studied by (1961FO07): see Table 12.6 (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). Cross section measurements are also reported at E_n = 7.55 MeV (1969HO1G: elastic, and inelastic to ¹¹B*(2.12, 4.45)), 9.72 MeV (1970CO12: elastic, and inelastic to ¹¹B states below 6.8 MeV), 14.1 MeV (1970AL08: elastic, and inelastic to ¹¹B states below 8.6 MeV) and 14.5 MeV (1970AN1F: ^natB). See also (1972LA1F), (1969AN1E, 1969MA39, 1969RO1F, 1970PO1E) and (1967BE1F; theor.).

12. (a) ¹¹B(n, p)¹¹Be Q_m = -10.726 E_b = 3.369
(b) ¹¹B(n, d)¹⁰Be Q_m = -9.005
(c) ¹¹B(n, t)⁹Be Q_m = -9.5591
(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 (1962KA37, 1966ST17, 1967FL16, 1967NA1C). See also (1971CU1B, 1971PR09, 1972ED01). For reaction (b) see ¹⁰Be in (1974AJ01). For reaction (c) see (1958WY67, 1972BI1E). See also ⁹Be in (1974AJ01). The cross section for reaction (d) has been measured by (1956AR21, 1959SA04, 1970SC29, 1973BO26) in the range E_n = 12.6 to 20.0 MeV, and at E_n = 25 and 38 MeV (1972KI19): no resonances are observed. See also ⁸Li in (1974AJ01) and (1968AJ02).

13. ¹¹B(d, p)¹²B Q_m = 1.145

Observed proton groups and gamma rays are displayed in Table 12.7 (in PDF or PS).

Angular distributions have been studied at many energies: see (1968AJ02) for earlier references and Table 12.7 (in PDF or PS). Recent interest has centered on the first unbound state in ¹²B, at E_x = 3.39 MeV: a DWBA analysis, when combined with information from ¹¹B + n (see reactions 10 and 11), finds l_n = 2 and is consistent with J^π = 3^- for ¹²B*(3.39) (1969FO10). See also (1971BU02; theor.). Assuming l_n = 2 to this state (1972DZ06, 1973DO02) analyzed the data in terms of a peripheral stripping model and calculated Γ_n = (1.9^+0.8_-0.6) eV for ¹²B*(3.39) [see also Table 12.6 (in PDF or PS)]. The probability p_3/2 for transfer of a neutron with angular momentum 3/2 has been determined for the p₀ and p₁ groups using vector polarized deuterons with E_d = 10 and 12 MeV (1970FI07).

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⁺, 2⁺ 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 12.13 (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).

See also (1967SP09, 1967TI1A, 1970WI17, 1973HOYD), (1973FI1C) and (1970VO09; theor.).

14. ¹¹B(t, d)¹²B Q_m = -2.888

Not reported.

15. ¹¹B(α, ³He)¹²B Q_m = -17.209

Not reported.

16. ¹²C(μ^-)¹²B Q_m = 92.289

Observation of γ-transitions has led to the determination of the capture rates to ¹²B*(0, 0.95, 1.67, 2.62) (1970BU1B, 1972MI15); those to ¹²B*(0.95, 1.67) are consistent with zero (1972MI15). Using polarized muons, (1974PO05) have determined the average polarization of ¹²B_g.s. to be 0.43 ± 0.10. See also (1970HI09).

17. ¹²C(n, p)¹²B Q_m = -12.588

At E_n = 54 MeV strong excitation of ¹²B*(0, 4.4, 7.8) is reported (1973KI1K). See also (1968AJ02) and ¹³C in (1976AJ04).

18. ¹²C(t, ³He)¹²B Q_m = -13.352

Not reported.

19. ¹²C(⁷Li, ⁷Be)¹²B Q_m = -14.232

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 = -17.534

At E_bs = 15 to 40 MeV, ¹²B*(0.95) is weakly excited (1971WI1N). See also (1973KI1J; theor.) and ¹³C in (1976AJ04).

21. ¹³C(d, ³He)¹²B Q_m = -12.041

At E_d = 28 MeV angular distributions have been measured for the ³He groups to ¹²B*(0, 0.95) (1972BR27). [See reaction 66 in ¹²C for a discussion of the population of the analog states in ¹²C in the mirror reaction ¹³C(d, t)¹²C.]

22. ¹³C(t, α)¹²B Q_m = 2.280

Not reported.

23. ¹⁴C(n, t)¹²B Q_m = -17.229

Not reported.

24. ¹⁴C(p, ³He)¹²B Q_m = -17.993

At E_p = 63.4 MeV, the excitation of the lowest T = 2 state in ¹²B is stated to be at E_x = 12.710 ± 0.020 MeV (1971NE1B, 1971NE1E: unpublished). This state has also been observed at E_p = 54 MeV as has another at E_x = 14.7 ± 0.1 MeV. The angular distribution of the lower state is consistent with L = 0; that for the higher state is rather featureless (D. Ashery, private communication) [see also reaction 70 in ¹²C]. See also (1970OL1B).

25. ¹⁴C(d, α)¹²B Q_m = 0.361

See (1968AJ02).

26. ¹⁴N(¹²C, ¹⁴O)¹²B Q_m = -18.515

At E(¹⁴N) = 118 MeV the excitation of ¹²B*(0, 0.95) is reported by (1974AN36).

27. ¹⁵N(n, α)¹²B Q_m = -7.622

See (1948JE03).

28. ¹⁸O(¹¹B, ¹⁷O)¹²B Q_m = -4.678

See (1974SW04).