A=12B (1968AJ02)

TUNL Nuclear Data
Evaluation Home Page

Information on mass
chains and nuclides

3 4

5 6

7 8

9 10

11 12

13 14

15 16

17 18

19 20

Group Info

Publications

HTML

General Tables

Level Diagrams

Tables of EL's

NSR Key# Retrieval

ENSDF

Excitation Functions

Thermal N Capt.

G.S. Decays

Half-Lives Table

TUNL Dissertations

NuDat at BNL

Useful Links

Citation Examples

Home

Sitemap

Directory

Email Us

WWW TUNL

¹²B (1968AJ02)

(See Energy Level Diagrams for ¹²B)

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

See (1956KU1A, 1959FL41, 1960TA1C, 1963RE1C, 1963RU1C, 1964MA2A, 1964NA1G, 1964ST1B, 1965UB1C, 1966MA1P, 1967HA10, 1967KE1K, 1967KE1L, 1967MO1R, 1968HI1C).

μ = +1.003 ± 0.001 nm (1967SU03).

1. ¹²B(β^-)¹²C Q_m = 13.370

Measured values of the half-life are displayed in Table 12.2 (in PDF or PS). The decay is complex; ¹²B decays to the ground state of ¹²C and to several excited states: see ¹²C. The transition to ¹²C_g.s. and (4.4) are allowed: hence J(¹²B) = 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). At E(⁷Li) = 2.6 MeV, a 1.67 MeV γ-ray is reported by (1962BE24). Angular distributions of protons have been determined by (1967GA06: E(⁶Li) = 3.5 MeV; p₀, p₁, p₂, p₃) and by (1967KI03: E(⁷Li) = 3.78 to 5.95 MeV; p₀, p₁, p₂, p₃₊₄, p₅). Except for p₂, the distributions are nearly isotropic. See also (1957NO14, 1962BE16).

3. ⁷Li(⁷Li, d)¹²B Q_m = 3.309

The gamma decay of the first four excited states has been studied by (1963CA09): besides the 0.95 MeV state, the states at 1.67 and 2.72 MeV decay primarily to the ground state ( > 98% and > 80%, respectively), while the 2.62 MeV state decays primarily via cascades through the 0.95 or 1.67 MeV states ( > 80%). τ_m(¹²B*(0.95)) = 295 ± 40 fsec; τ_m(¹²B*(1.67)) < 50 fsec (1967THZX). See also ¹¹B(d, p)¹²B. See also (1962BE24, 1967WY1B) and ¹⁴C in (1970AJ04).

4. ⁹Be(t, n)¹¹B Q_m = 9.561 E_b = 12.930

Reported resonances in the yield of neutrons at θ = 0° are listed in Table 12.3 (in PDF or PS) (1961VA1C). See also (1962SE1A).

5. ⁹Be(α, p)¹²B Q_m = -6.884

See (1951MC57, 1955RA41, 1962WE1C).

6. ⁹Be(⁷Li, α)¹²B Q_m = 10.463

At E(⁷Li) = 3.5 MeV, α-groups are seen to the ground state of ¹²B and to levels at 0.90, 1.61, 2.58, 3.27, 3.60, 4.22, 4.39, 4.90, 5.60, 5.80, 6.61, 7.00, 7.42, 7.77, 8.05, 8.34 and 9.06 MeV. Angular distributions have been obtained for the first five states for E(⁷Li) = 3.3, 3.5 and 3.75 MeV. The total cross sections range from 1.1 to 2.3 mb. All angular distributions are characterized by backward maxima (1961HO19). See also (1966RO1E).

7. ⁹Be(¹¹B, 2α)¹²B Q_m = 1.799

See (1963HO1E).

8. ¹⁰B(t, p)¹²B Q_m = 6.343

Eleven excited states of ¹²B have been observed by (1960JA17) at E_t = 5.5 MeV and by (1964MI04) at E_t = 10 MeV. Widths and J^π values derived from angular distribution analyses (1964MI04) are displayed in Table 12.4 (in PDF or PS). See also (1963HO19) and (1965SH1E, 1966SH1F, 1967BA1E; theor.).

9. ¹¹B(n, γ)¹²B Q_m = 3.369

The thermal neutron capture cross section is 5 ± 3 mb (1962IM01). The excitation function of β^- particles (from ¹²B decay) shows a resonance at E_n = 20 keV, with ωΓ_γ ≈ 0.4 eV, Γ < 10 keV (1964MO07). 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).

10. ¹¹B(n, n)¹¹B E_b = 3.369

The thermal (bound) scattering cross section for B is 4.4 ± 0.2 b (1958HU18, 1961WI1A). The scattering amplitude (bound) is a = 6.6 ± 0.3 fm (1965DO14), 6.53 ± 0.35 fm (1966DO11). Parameters of observed resonances in σ_tot are listed in Table 12.5 (in PDF or PS). The resonance at E_n = 20 keV (1966MO09) is also observed in ¹¹B(n, γ)¹²B (1964MO07). Angular distributions near the E_n = 0.43 MeV resonance (J = 2) show cosθ terms, indicating interference with s-wave potential scattering. The best fit to the data is obtained with l = 1 formation of the resonance, either all channel spin 1 or all channel spin 2 (1955WI25). Polarization results can be explained by interference of s- and p-wave neutrons at this resonance (1962EL01). The E_n = 1.28 MeV resonance can be fitted with J = 3, l = 2 with the partial width in channel spin 2 equal to 10 times that in channel spin 1. Potential scattering at E_n = 1.5 MeV is nearly all s-wave, δ₀ = -90° (1955WI25). A resonance not seen in earlier work is reported by (1962IM01) at E_n = 1.027 MeV. The observed cross section is consistent with s-wave formation, J^π = (1)^-. Polarization and differential cross section measurements have been carried out at 70 neutron energies from 0.075 to 2.25 MeV. Large polarizations are observed from the resonance at E_n = 1.28 MeV up to 2.25 MeV. Resonance behavior of the interference terms indicates that the parities of ¹²B*(4.54) and (5.00) must be opposite (1967LA1N).

Total cross sections from E_n = 3.4 to 15.5 MeV have been studied by (1961FO07): 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. Total cross sections from E_n = 14.1 to 18.0 MeV are reported by (1954CO16).

See also (1963BA1F, 1963KU1F, 1963NE1H, 1965MO1J, 1967MA1K) and (1963LU10, 1966AG1A; theor.) and (1959AJ76).

11. (a) ¹¹B(n, d)¹⁰Be Q_m = -9.004 E_b = 3.369
(b) ¹¹B(n, t)⁹Be Q_m = -9.561
(c) ¹¹B(n, α)⁸Li Q_m = -6.632
(d) ¹¹B(n, p)¹¹Be Q_m = -10.731

Reaction (a) has not been reported. At E_n = 14.1 MeV, the cross section for reaction (b) is 15 ± 5 mb (1958WY67). 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 is 35 ± 7 mb (1959SA04; see also (1962KA37, 1963CH20, 1966MO09)). The cross section for reaction (d) has been measured for E_n = 14.7 to 16.9 MeV (1962KA37, 1966ST17). See also (1959AL83, 1964ST25).

12. ¹¹B(d, p)¹²B Q_m = 1.144

Observed proton groups and gamma rays are displayed in Table 12.6 (in PDF or PS). Angular distributions of protons leading to the ground and 0.95 MeV states are of special interest because of the low Q-value: see studies by (1953HO48, 1961GO27, 1961GO28, 1961PU1B, 1962GO24, 1963RO22, 1963SE1F, 1963SE1G, 1964FI1D, 1964TI03, 1965BE1V, 1965FI05, 1965GA02, 1965LO02, 1965SA15, 1966GA09, 1966HA10, 1967BO17, 1967MO1Q, 1967SC29). Spectroscopic factors are listed by (1965GA02, 1966GA09, 1967MO1Q, 1967SC29). Polarization of the recoil ¹²B is reported by (1959CH1D, 1967SU03).

The 0.95 MeV level is formed by p-wave capture, J^π = 0⁺, 1⁺, 2⁺ or 3⁺. The observed anisotropy of the γ-radiation (1960KO03, 1963WA20, 1965BE1V) excludes J = 0. The mean life of the state is 0.30 ± 0.033 psec (1968OL01). So short of a life excludes pure E2 radiation and hence J ≠ 3, and limits δ² ≡ E2/M1 intensity ratio to < 0.02 for J = 1 or 2 (1963WA20). The observed polarization of the γ-ray also excludes J = 3 (1965BE1V). Gamma-γ correlations in the cascade 1.67 → 0.95 → g.s. fix J = 2; the amplitude mixing ratio δ ≡ E2/M1 for γ (0.95) is in the range -0.124 → 0.00 (1968CH05). The energy of the level is 953.14 ± 0.60 keV (1966WI01). The observed Γ_γ = 2.2 ± 0.25 meV and the mixing rates E2/M1 are in satisfactory agreement with IPM predictions (1968OL01). See also (1961GO27, 1961GO28, 1966BE31, 1967BO17).

The 1.67 MeV state is formed by s-wave capture, J^π = 1^- or 2^-. The gamma decay is mainly direct, with a (3.2 ± 0.5)% (1968OL01), 3.0 ± 0.6% (1968CH05) branch via ¹²B*(0.95): τ_m < 50 fsec (1968OL01). See also (1964CH04, 1963WA20, 1965GA02). Gamma-γ correlations lead to an assignment J^π = 2^- (1964CH04, 1965GA02, 1968CH05). The energy of the level is 1673.65 ± 0.60 keV (1966WI01).

The 2.62 MeV level is formed by s-wave capture, J^π = 1^- or 2^- (1962GO24, 1965GA02). The level decays mainly via ¹²B*(0.95) (80 ± 3)%. The ground-state branch is (6 ± 1)% (1968OL01): τ_m < 70 fsec (1968OL01). See also (1963WA20, 1965GA02). Gamma-γ correlations lead to J^π = 1^-. E_x = 2620.8 ± 1.2 keV (1968OL01), 2618.5 ± 3.5 keV (1964CH04, 1966WI01). See also (1965GA02).

The 2.72 MeV level is only weakly excited; most probably l_n = 1, J^π < / = 3⁺, although l_n = 0, 2 are not excluded (1965GA02). The decay is mainly, if not entirely, ( > 85%) to the g.s. (1968OL01): see also ⁷Li(⁷Li, d)¹²B.

The 3.39 MeV state is formed by l_n = 1 (1953HO48); Γ_γ/Γ < 0.1 (1965GA02). See also (1963BR16, 1966BE1E, 1966GO1L, 1966SC23, 1967CH19).

13. ¹¹B(t, d)¹²B Q_m = -2.888

Not reported.

14. ¹¹B(α, ³He)¹²B Q_m = -17.209

Not reported.

15. ¹²C(n, p)¹²B Q_m = -12.588

See (1948JE03, 1959AL83, 1967ME11) and ¹³C in (1970AJ04).

16. ¹²C(t, ³He)¹²B Q_m = -13.352

Not reported.

17. ¹³C(γ, p)¹²B Q_m = -17.535

See (1963NE02) and ¹³C in (1970AJ04).

18. ¹³C(d, ³He)¹²B Q_m = -12.041

Not reported.

19. ¹³C(t, α)¹²B Q_m = 2.280

Not reported.

20. ¹⁴C(n, t)¹²B Q_m = -17.229

Not reported.

21. ¹⁴C(p, ³He)¹²B Q_m = -17.993

Not reported.

22. ¹⁴C(d, α)¹²B Q_m = 0.361

See (1950HU72, 1956DO41).

23. ¹⁴N(n, ³He)¹²B Q_m = -17.366

Not reported.

24. ¹⁵N(n, α)¹²B Q_m = -7.623

See (1948JE03).