A=12B (1959AJ76)

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¹²B (1959AJ76)

(See the Energy Level Diagram for ¹²B)

GENERAL: See also Table 12.1 [Table of Energy Levels] (in PDF or PS).

Theory: See (1956KU1A, 1958FR1C).

1. ¹²B(β^-)¹²C Q_m = 13.376

The spectrum is complex: see ¹²C. The transition to ¹²C_g.s. is allowed; hence J(¹²B) = 1⁺.

2. ⁶Li(⁷Li, p)¹²B Q_m = 8.338

Three groups of protons are reported, corresponding to the ground state and to the excited states at 0.95 and 1.67 MeV. At E(⁷Li) = 2.0 MeV, θ = 90° (lab), the relative intensities are 1 : 1.1 : 0.8 (1957NO14). See also (1957NO17).

3. ⁷Li(⁷Li, d)¹²B Q_m = 3.311

See ¹⁴C.

4. ⁹Be(α, p)¹²B Q_m = -6.884

At E_α = 21.7 MeV, proton groups are observed corresponding to ¹²B*(0, 0.95, 1.65, 3.38, 3.82) (1951MC57, 1955RA41).

5. ⁹Be(⁷Li, α)¹²B Q_m = 10.463

See (1957NO17).

6. ¹⁰B(t, p)¹²B Q_m = 6.344

At E_t = 0.90 MeV, proton groups are observed corresponding to ¹²B*(0.94, 1.65, 2.61, 3.37, 3.75, 4.46) (1955BI26: ± ≈ 0.1 MeV).

7. ¹¹B(n, γ)¹²B Q_m = 3.365

σ_th < 50 mb (1958HU18). See also (1953WI1C).

8. ¹¹B(n, n)¹¹B E_b = 3.365

The parameters of observed resonances at E_n = 0.43, 1.28, 1.78, 2.45 and 2.58 MeV are exhibited in Table 12.2 (in PDF or PS). The rise of the cross section at low energies may indicate a broad level formed by s-wave neutrons (1951BO45). The angular distributions of elastically scattered neutrons have been studied for E_n = 0.43 to 1.50 MeV by (1955WI25). It is found that the 0.43-MeV resonance has J = 2⁺, formed by p-waves, either all in channel spin 1 or all in channel spin 2. The 1.28 MeV resonance had J = 3^-, formed by d-waves, with the level width of channel spin 2 about 10 times that of channel spin 1. Potential scattering at E_n = 1.5 MeV is nearly all s-wave: δ₀ = -90° (1955WI25).

The total cross section for natural boron shows no sharp discontinuities for E_n = 4.4 to 5.6 MeV (σ ≈ 1.6 b) and for E_n = 7.8 to 8.6 MeV (σ ≈ 1.4 b) (1956BE98). The total cross section has also been measured for E_n = 6 to 9.7 MeV (1954NE1A) and from E_n = 14.1 to 18.0 MeV by (1952CO41, 1954CO16); see (1955HU1B). See also (1955HI1C, 1956LA1C, 1957LA14, 1958HU18). At E_n = 14.5 MeV the non-elastic cross section for natural boron is 0.64 ± 0.04 b (1956FL1B).

9. (a) ¹¹B(n, d)¹⁰Be Q_m = -9.010 E_b = 3.365
(b) ¹¹B(n, t)⁹Be Q_m = -9.564
(c) ¹¹B(n, α)⁸Li Q_m = -6.636
(d) ¹¹B(n, p)¹¹Be Q_m = -10.69

The cross section for reaction (c) decreases from 27 mb at E_n = 12.6 MeV to 16 mb at E_n = 20.0 MeV (1956AR21). At E_n = 14.1 MeV, the cross section for reaction (b) is 15 ± 5 mb (1958WY67). Reaction (a) has not been reported. See also (1954HE1B). For reaction (d) see ¹¹Be.

10. ¹¹B(d, p)¹²B Q_m = 1.138

Proton groups observed at E_d = 4.0 to 8.5 MeV are listed in Table 12.3 (in PDF or PS). No other groups are observed for E_x = 0 to 3.15 MeV with an intensity greater than 4% of the ground-state group, or from 3.15 to 3.5 MeV excitation with an intensity greater than 8% (1953EL12). See also (1954KH1A, 1955KH35). Angular distributions and absolute cross sections have been determined at E_d = 8 MeV. Analysis by stripping theory leads to the assignments indicated in Table 12.3 (in PDF or PS). Neutron capture probabilities are compared with expected single-particle values to eliminate certain spin possibilities (1953HO48). At E_d = 1.05 MeV, γ-rays with energy 0.94 and 1.64 MeV are observed with an intensity ratio of 2 : 1 (1954TH1B). See also (1955RA41, 1956KA1A, 1956TA07, 1957CH25, 1957CO59).

11. ¹¹B(t, d)¹²B Q_m = -2.894

Not reported.

12. ¹¹B(α, ³He)¹²B Q_m = -17.213

Not reported.

13. ¹²C(n, p)¹²B Q_m = -12.593

See (1948JE03).

14. ¹²C(t, ³He)¹²B Q_m = -13.358

Not reported.

15. ¹³C(γ, p)¹²B Q_m = -17.539

See ¹³C.

16. ¹³C(d, ³He)¹²B Q_m = -12.045

Not reported.

17. ¹³C(t, α)¹²B Q_m = 2.274

Not reported.

18. ¹⁴C(n, t)¹²B Q_m = -17.228

Not reported.

19. ¹⁴C(p, ³He)¹²B Q_m = -17.993

Not reported.

20. ¹⁴C(d, α)¹²B Q_m = 0.358
Q₀ = 0.362 ± 0.0015 (1956DO41).