(See 12.5 (in PDF or PS) and Energy Level Diagrams for 12B and Isobar Diagram)
Q = 1.32 ± 0.03 fm2 (1993OH05). See also 1.34 ± 0.14 fm2 (1978MI19).
< r2matter >1/2 ≈ 2.31 - 2.35 fm; i.e., see (1988TA10, 2010LI18, 2014ES07).
The half-life of 12B is 20.20 ± 0.02 ms (1978AL01); earlier values are reported in (1968AJ02). 12B decays to 12C*(0, 4.4, 7.7, 10.3, 12.7); states in 12C above Ex = 7366 keV are unbound to α-decay: see details in 12.24 (in PDF or PS). The transitions to 12Cg.s.[Jπ = 0+] and 12C*(4.4[Jπ = 2+]) are allowed; hence the Jπ of 12Bg.s. is 1+.
Values of the magnetic dipole moment, μ = 1.0002 ± 0.0028 μN (2003ZH32), μ = 1.003 ± 0.001 μN (1997MA21) and μ = 1.001 ± 0.017 μN (2010ZH03), were measured using β-NMR techniques, and the (electric) quadrupole moment, Q = 13.22 ± 0.26 mb (1993MI36, 1993OH05, 1994OH03) was measured using β-NQR techniques; these compare well with the presently adopted values: see (2016ST14). A β-Level Mixing Resonance method, which simultaneously gives information on the nuclear alignment, μ and Q values, is applied to 12B in (1997NE01, 1999CO09, 2001CO09).
See other theoretical work in (1993KI05, 1993KI22, 2012YU07, 2014RA17), and see discussion on methods for polarizing 12B in (1984KO25, 1985DE54, 1990NO14, 1993SH37, 1997CO15, 1997MA21, 1998MA27, 1999MA24, 2002MO44, 2004NA37, 2007GR23) and references cited in (1985AJ01, 1990AJ01). See discussion on using TiO2 (2001OG12, 2002OG08) and superfluid 4He (1995SH22, 1996TA12, 1997TA13) as nuclear spin dewars. Quadrupole coupling constants of polarized 12B in Mg and Zn were measured in (1993OH11).
The G-parity irregular induced tensor coefficient in the weak nucleon axial vector current 2MfT/fA = -0.21 ± 0.09 (stat.) ± 0.07 (sys.) ± 0.05 (theory) (2002MI03) was deduced from the alignment correlation terms in spin aligned 12B and 12N decay. When combined with reanalyzed results from (1998MI14, 1999MI41, 2000MI11) the new analysis gives 2MfT/fA = -0.15 ± 0.12 ± 0.05 (theory) (2002MI03, 2002MI49, 2003MI24); see also (1987MI20) and (1995KO28: theory).
The axial charge in the weak nucleon axial vector current y = 4.96 ± 0.09 (stat.) ± 0.05 (sys.) (2002MI01, 2002MI36) was deduced from the alignment correlation terms in spin aligned 12B and 12N decay. When combined with reanalyzed results from (1993MI32, 1994MO23, 1998MA27, 1999MI04, 1999MI41, 2000MI11) the new analysis gives y = 4.90 ± 0.10 (2002MI01). The large mesonic enhancement to the axial charge observed in the A = 12 triad may suggest an "in-medium" nucleon mass reduction of ≈ (16 ± 4)% (2002MI01). See also (2003SM02).
The β- spectral shape following 12B decay was measured (1987NA08, 1990CA10, 2000ST19) and compared with the β+ spectral shape following 12N decay to determine the weak magnetism correction to the beta spectra (1990CA10). Shape factors for β and ν spectra are compiled in (2015MO10). See Knight shifts measurements reported in (2007MI49) and other discussion in (1992BA11, 1993CH06).
At E(14C) = 17.1 MeV/A , 12B states at Ex = 0, 953, 3759, 5000 and 5612 were populated using (d, α) reactions in inverse kinematics. The high spin selectivity of the reaction, which favors states with large J values, strongly populated the 12B*(5612) Jπ = 3+ state (2014WU10).
Eleven groups of protons are reported to the known states at Ex ≤ 5.6 MeV (1959MO12). Angular distributions have been measured at E(6Li) = 3.5 to 5.95 MeV. The distributions are generally featureless.
Angular distributions have been measured at E(7Li) = 2.10 to 5.75 MeV (1969CA1A: d0, d1, d2, d3+4). The γ-decay of the first four excited states has been studied by (1963CA09): 12B*(0.95) decays 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 12.7 (in PDF or PS) in (1975AJ02). The mean lifetimes of 12B*(0.95, 2.62) are 295 ± 37 fsec and <48 fsec, respectively (1969TH01).
At E(7Li) = 58 MeV the 7Li(7Li, 12B*) → (9Be + t and 8Li + α) reactions were studied (2005CU06); see 12.6 (in PDF or PS). Observations indicate α+Li clusters play an important role in the boron isotopes. See also (1984KO25).
Reaction cross sections have been measured at Ecm = 0.6 to 2.7 MeV (2004HA54, 2006IS04), Ecm = 0.6 to 5 MeV (2016DE02), Ecm = 0.64 to 2.2 MeV (1995GU02), Ecm = 0.9 to 2.8 MeV (2004MI34), Ecm = 1.05 MeV (2008LA08, 2010LA07), Ecm = 1.25 MeV, Ecm = 1.5 to 7 MeV (2000MI34) and E(8Li) = 10 to 20 MeV (1992BO06). Various unresolved 12B resonances are observed. Rates for the reaction path 8Li(α, n)11B(n, γ)12B(β-)12C are crucial for computing the formation of A > 12 nuclei in inhomogeneous Big Bang Nucleosynthesis (1992BO06, 1993DE30, 2000MI34, 2004CH22). Early estimates for the 8Li(α, n) reaction rate were based on the inverse reaction, 11B(n, α), which only samples the 8Li(α, n0) rate. The direct measurements indicate the total σ to all 11B excited states is roughly five times larger than the branch that feeds only 11Bg.s. (1992BO06). Systematic issues are evident when comparing inclusive (8Li, n) and exclusive (8Li, n + 11B) results: see (2006IS04). A novel experiment approached the issue by impinging a 8Li beam on a 4He gas target that was located inside a zero-energy-threshold 4π 3He proportional counter embedded in a polyethylene moderator (2004CH22, 2008LA08, 2010LA07). See (2000MI34) for branching ratios to n0 through n9. Also see discussion in (1990DE21, 1992RA04, 1993OB01, 1994KU28, 1996DE02, 2012CO01, 2012LA20, 2016DE02). The fusion barrier is studied in (2016DE02).
Elastic α scattering on 8Li was measured in thick target inverse kinematics by impinging a Ecm = 10.2 MeV 8Li on a 4He gas cell and detecting the scattered α-particles (2011TO05, 2012DI22). Broad structures at Ex ≈ 13.6, 14.4, and 15.8 MeV dominate the excitation function.
The role of 9Li(α, n)12B(β-)12C in astrophysical processes is evaluated in (2010HO09).
Thirteen resonances have been reported in reaction (a) corresponding to 13.6 < Ex < 14.7 MeV: see 12.7 (in PDF or PS). Optical potentials for 9Be + t are analyzed in (2007LI55, 2009PA07, 2015PA10). The yield of 2.12 MeV γ-rays has been measured for Et = 1.5 to 3.3 MeV, Et = 2.96 to 11.46 MeV (2001GE16), and E(9Be) = 10 to 16 MeV: no resonances are observed. This is also the case for the yields of 0.32 MeV (reaction (b)), 0.98 MeV (reaction (e)) and 0.48 MeV γ-rays (from the (t, αn) reaction). Elastically scattered tritons have been studied for Et = 0.60 to 2.1 MeV and Epol. t = 15 and 17 MeV (also Ay). The yields of α0 and α1 have also been reported for Et = 0.52 to 1.70 MeV: see (1975AJ02). The analyzing powers of the reactions leading to 6Heg.s. and 6Li*(0, 3.56) have been measured at Epol. t = 17 MeV. For references see (1985AJ01). See also (1988AJ01).
Observed proton groups, above Ex = 7.6 MeV are displayed in 12.8 (in PDF or PS). Early studies of low-lying states were carried out at Eα = 21.7 MeV (1951MC57, 1955RA41). The later studies at Eα = 29, 35.2 and 39.7 MeV (1994MA05, 1994MA06), Eα = 50.29 (1991KU31) and Eα = 65 MeV (1991KU10, 1992BO16) evaluated neutron unbound states that can participate in the astrophysically important 8Li(α, n) and 9Li(t, n) reactions. In (1991KU31, 1994MA06) the scattered protons, which determine the 12B excitation energy, are measured in coincidence with neutrons, and the angular distributions of the n0-3-decay neutrons are analyzed to constrain l and Jπ values. The work of (1994MA06) studies the astrophysical significance of 12B*(10.119 to 11.571) states by considering Γ, Γn0-3, Γn, Γα, and allowed spin values deduced in their analysis. Of particular importance (1994MA05) find no evidence for a state at Ex ≈ 10.6 MeV with Γ ≈ 200 keV that is reported by (1990PA22) and is suggested to dominate the S-factor. See also unpublished work cited in (1985AJ01).
At E(6Li) = 32 MeV 12B*(0, 0.95, 1.67, 3.38, 3.76) and some unresolved states are populated (1986AS02).
Observed α-particle groups are displayed in 12.9 (in PDF or PS). Angular distributions have been measured at E(7Li) = 3.3 to 6.2 MeV, at 20 MeV and at 30.3 MeV: see (1975AJ02, 1980AJ01). At E(7Li) = 20 MeV angular distributions to the first seven states are rather featureless and have approximate symmetry about 90°. The integrated cross sections go as 2Jf + 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.
At E(7Li) = 52 MeV states at 12B*(10.9, 11.6, 13.4, (14.1), 15.7, (17.7)) were observed in the complete kinematic reconstruction of 2α + 8Li ejectiles from 9Be(7Li, 12B* → α + 8Li)α reactions (2003SO22, 2003SO29).
Total reaction and interaction cross sections are reported at E(12B) = 54.4 MeV/A on natSi (2010LI18), at E(12B) = 64 MeV/A on natC (2004SA14), at E(12B) = 67 MeV/A on natC (2000SA47), at E(12B) = 790 MeV/A on 9Be, natC, 27Al (1988TA10), at E(12B) = 920 MeV/A on 12C (1999BO46), at E(12B) = 930 MeV/A on natC (2000CH20), and on Cu (1989SA10). Glauber model analyses suggest Rmatterrms ≈ 2.33 fm (2010LI18) and 2.31 ± 0.07 fm (2014ES07). See also (1990LI39, 1990LO10, 1999KN04, 2000BH09, 2000CA33, 2001OZ04, 2002BR01, 2003CA07, 2004CA45, 2006BH01, 2006SH20, 2011KU06).
The cross sections for production of 8Li (reaction (b)) and of 11Be (reaction (a)) have been measured for Ed = 0.67 to 3.0 MeV and 2.3 to 12 MeV, respectively: the yields for both reactions vary smoothly with energy. No resonances are observed: see discussion in (1975AJ02). See also (2012UP01).
Observed excited states are displayed in 12.9 (in PDF or PS). Angular distributions have been studied at Et = 10 and 23 MeV: see (1980AJ01). The angular distributions are analyzed in a search for manifestation of a 12B neutron or dineutron halo (2008GA09, 2009GA33). See also (2012GA20: theory).
The thermal neutron capture cross section, σth = 9.09 ± 0.10 mb, is reported by (2016FI06). This compares with σth = 5.5 ± 3.3 mb [see (1981MUZQ, 2003MOZU); see also the value σ = 9.07 ± 0.22 mb from (2008FIZZ)]. In (2016FI06), the thermal capture state is reported to decay to 12B*(0, 953) with Iγ = (70.8 ± 0.5)% and (29.2 ± 0.5)%, respectively.
The capture cross section was deduced by measuring the 12B decay activity and shows resonances at En = 20.8 ± 0.5 keV and at 0.43, 1.03, 1.28 and 1.78 MeV, with Γγ = 25 ± 8 meV and 0.3, 0.3, 0.2 and 0.9 eV (± 50%): see 12.10 (in PDF or PS) and (1968AJ02). For a summary and the ENDF projections see (2010PR07, 2012PR13). See also (1988MA1U, 2010HU11, 2012CO01, 2014DU09: astrophys.).
The thermal (bound) scattering cross section is 3.9 ± 0.2 b. The scattering amplitude (bound) is a = 6.65 ± 0.04 fm, σ(free) = 4.84 ± 0.04 b (1983KO17). The neutron spectroscopic factor is analyzed in (2009TI11). Total cross-section measurements have been reported for En = 0.3 to 18.0 MeV: see (1995DO36) and references in (1968AJ02, 1980AJ01, 1985AJ01). Parameters of analyzed resonances are shown in 12.10 (in PDF or PS). See additional structures observed in (1979AU07, 1995DO36). For a summary and the ENDF projections see (2010PR07, 2012PR13). High energy results are discussed in (2001AB14: En ≤ 600 MeV) and (2011SU23). For differential cross sections see 11B. Polarization measurements have been carried out at En = 75 keV to 2.2 MeV [see references in (1980AJ01)].
The cross sections for reaction (a) have been measured for En = 14.7 to 16.9 MeV and those for reaction (b) have been investigated for En = 12.6 to 20.0 MeV and at 25 and 38 MeV: see (1975AJ02). Reaction (d) was measured for En = 7.6 to 12.6 MeV (1990PA22, 1991PA26) in an effort to evaluate the inverse 8Li(α, n0) reaction via the detailed balance theorem; a resonance at Ecm(res) = 580 keV with Γcm ≈ 200 keV is reported to dominate the cross section; however such a resonance has not been observed in other studies; see (1994MA06) and 12B reaction 8Li(α, n). Earlier measurements are reported at En = 14.4 MeV (1979AN18), and at En = 12 to 38 MeV : see (1975AJ02); no resonances were observed. For a summary and the ENDF projections see (1988MCZT).
The cross section for π+ production near threshold has been measured. At Ep = 200 MeV 12B*(0, 0.95, 1.67, 2.62, 3.39, 3.76, 4.30 + 4.52, 5.00, 5.61) are reported: see (1985AJ01).
The 12B nucleus was first identified in the analysis of β-decay species produced using this reaction (1935CR02, 2012TH01). Observed proton groups and γ-rays are displayed in 12.11 (in PDF or PS). Angular distributions of cross sections to 12Bg.s. were measured at Ed = 76 to 144 keV (1997YA02, 1997YA08). A study in (2010LE02) analyzed angular distributions for protons leading to 12B*(0, 0.95, 1.67, 2.62, 3.39, 4.30); revised spectroscopic factors were deduced for 12B*(3.39, 4.30) and a partial width of Γn/Γγ = 95 ± 5 was obtained for 12B*(3.39); implications on the 11B(n, γ) astrophysical reaction rate are discussed. See also (2012CO01). At Ed = 26.3 MeV angular distributions of protons to 12B*(10.199, 10.564, 10.880) were analyzed to find total widths and to evaluate the spin quantum numbers via DWBA analysis (1994MA05); widths of Γ = 9 ± 3 keV, 11 ± 4 keV and 16 ± 6 keV are deduced, respectively (1994MA05).
Discussion of this reaction in (1968AJ02) justifies Jπ = 2+, 2- and 1- assignments for 12B*(0.95, 1.67, 2.62), respectively. See 12.10 (in PDF or PS) in (1980AJ01) for a comparison of reduced widths and spectroscopic factors of the first seven T = 1 states in 12B and in 12C. Earlier work is referenced in 12.13 (in PDF or PS) of (1975AJ02).
The 11B + n → 12B*(0, 2.62, 2.73) asymptotic normalization coefficients were deduced from DWBA analysis of angular distribution measurements at Ed = 11.8 MeV (2001LI42, 2001LI45); analysis suggests a neutron halo structure for the two higher states. In (2003LI50) analysis of the ANCs provides a result for the direct capture component of the 11B(n, γ) reaction at astrophysical energies; see also reaction 11B(n, γ). In (2007GU01), the existing 11B(d, p) data is analyzed to extract ANCs for 11B + n → 12B*(0, 0.95, 1.67); then, using charge symmetry, the ANC for 12N → 11C + p is deduced and used to determine the direct capture component for 11C(p, γ); see also (2010TI04, 2012OK02, 2013TI05) and 12N reaction 11C(p, γ).
At E(7Li) = 34 MeV angular distributions to 12B*(0, 0.95, 1.67, 2.62 + 2.72, 3.39, 4.52, 5.61 + 5.73) are measured, and spectroscopic factors are deduced (1987CO16).
Observation of 4.44 MeV γ-rays from 12Bg.s. decay to 12C and β-delayed neutrons from 12B* decay to 11B + n provide evidence that at least two 12B states are fed in 12Be decay; however no detailed decay scheme has been experimentally deduced (1994KE06). Using the 12Be half-life, 21.46 ± 0.05 ms (see 12Be reaction 1), and assuming a (99.50 ± 0.03)% branching ratio to the ground state (1999BE53) gives log ft = 3.7952 ± 0.0017 for that decay.
For reaction (a), angular distributions for the ΔS = 1, ΔT = 1 spin-isospin flip excitation states at 12B*(0, 0.95, 4.5, 7.5, 10, 13) were measured using tagged Ebrem = 187 MeV (1990SO06) and 191 MeV (1994CH39, 1994CH43) beams. DWIA calculations of the angular distributions are used to analyze the transition multipolarities for states up to Ex = 7.5 MeV. Earlier work with Eγ = 210 to 381 MeV (1982AR06) measured the total cross section for π+ emission and the spectra of the positive pions; the Eγ = 381 MeV data show the influence of quasi-free pion production and FSI processes. See also DWIA (1990ER03, 1991OD04, 1995DO24), PWIA (2007TR04), Shell Model (1991ER06) and many-body (1992CA16) analyses.
At Ee = 195 to 205 MeV the π+ energy distributions show contributions from 12B*(0, 0.95, ≈ 4.5, 7.0): see (1986SH14, 1988SH36) and references in (1985AJ01). The 2- and 4- states at Ex ≈ 4.5 MeV have been compared with their isobaric analogs in 12C at Ex ≈ 19.5 MeV (1980MI08). At Ee = 400 MeV, π+ with Eπ = 32 MeV have been studied: double differential cross sections are obtained for the transitions to 12B*(0, 0.95, 1.67), and single differential cross sections to 12B*(0, 0.95) (1983SC03, 1983SC11); the cross section (at θ = 54°) is the same whether virtual or real photons are used in producing the pions (1983SC03). At Eγ = 176 to 187 MeV the giant resonance region, as well as some lower groups, has been studied by (1987MIZZ). Nuclear transparency vs. Q2 was studied at Ee ≈ 5.8 GeV (2007CL04, 2009KA02, 2010QI02). See also (1988SH36, 1997GI13, 2002DI04, 2016LA08). Differential cross sections for photoproduction of two pions were analyzed for Eγ = 400 to 460 MeV using a tagged Bremsstrahlung beam (2002ME22); see theoretical analysis in (2003ME32, 2003RO20, 2003VI09, 2003VI11, 2004MU17, 2006SC18).
Strangeness electro-production measurements and discussion of nuclear medium effects are given in (1994MA42, 1994MO49, 1995YA10, 1998LE23) for reaction (a) and (1992AD09, 1998HI15, 2003MI11, 2004FU34, 2006YU03, 2007IO02) for reaction (b).
Theoretical analysis is given on the neutrino induced Charge Current reactions 12C(νe, e+)ν̄ (1982MI05, 1992KO07, 1995KO40, 2002JA03, 2005BO44, 2006CO15, 2006CO16, 2011SA04, 2013SO15) and 12C(νμ, μ+)̄ν (1982MI05, 1995KO40, 1996EN06, 1996KO03, 2002JA03, 2008IV01, 2011KI06, 2014KI06, 2014PA06, 2016PA43). See also 12N reactions 9 and 10 for more discussion.
Observations of γ-transitions have led to the determination of the capture rates to 12B*(0[Jπ = 1+], 0.95[2+], 1.67[2-], 2.62[1-]) (1981GI08, 1981RO15); see also (1972MI15). The branching ratios for a variety of nuclides populated in 12C + μ-stopped reactions is reported in (2016AB02). See theoretical discussions in (1998MU17, 1998SI11, 2000HA17, 2002AU01, 2002JA03, 2005AM08, 2005NI01, 2006AM06, 2006VA09).
The ratio of the polarization of 12Bg.s., Pave, and of the longitudinal polarization, PL, has been determined by (1981RO05, 1981RO15, 1982RO13): this ratio leads to a neutrino helicity, hν = -1.06 ± 0.11 (1981RO15), in agreement with the partial conservation of axial-vector current (PCAC) hypothesis. The polarization of 12B has also been directly measured by (1984KU20): Pave is deduced to be 0.462 ± 0.053 yielding a ratio of the induced pseudoscalar to the axial vector coupling constant in the hadronic weak current, gp/ga = 10.1+2.4-2.6, which is consistent with the prediction of ≈ 7 from Parity Conserved Axial-vector Current (1984KU20). See earlier measurements of Pave and PL in (1974PO05, 1977PO1B, 1979TR05) and (1989KA35, 1994KO27, 2002AU01: theory).
The branching ratio for "radiative muon capture" (reaction (b)) is Rγ = (2.33 ± 0.17) × 10-5 when compared with the dominant process of "ordinary muon capture" (reaction (a)) (1991AR02). The branching ratio for radiative capture depends on the induced pseudoscalar coupling constant, gp, and measurements on 12C, 16O and 40Ca show strong target dependence for the gp/ga values deduced from radiative capture (16.2+1.3-0.7, 13.6+1.6-1.9, and 4.6 ± 1.8, respectively: 1991AR02 [in this result, renormalization is not strongly advocated, but rather more consistency in the theoretical treatment of the nuclear response]). See other results in (1988DO05) and (1989NA01, 1990GM01, 1990RO04, 2000KO06: theory).
The photon spectrum from stopped pions is dominated by peaks corresponding to 12B*(0, 4.4, 7.9) (1970BI10). Branching ratios have been obtained for these and other unresolved transitions; that to 12Bg.s. is (6.22 ± 0.35)% (absolute branching ratio per stopped pion) (1986PE05); see also (1997AM04: theory). The branching ratio for 12C(π-, 2γ) is (1.2 ± 0.2) × 10-5 (1980MA39); see also (1995GI09: theory).
At Eπ = 165 MeV, excitation of the 12N and 12B isovector analog giant E1 resonances, built on 12Cg.s., is observed (1994HA41). Transitions to the ground states of 12B and 12N, via 12C + π∓, are discussed as a means to understand the difference in ft-values for 12B and 12N decay to 12Cg.s. (1970HI10). Studies of (π±, π0) evaluate the A and isospin dependence of the cross section for the Δ-nucleus interaction in (1983AS01, 1984AS05, 1990BE41); see also (1987CL02) for a study of delta production at Eπ- = 475 MeV. Analysis of scaling and scaling systems is given in (2013PE24). See (1996NA04) for a measurement with stopped pions.
Experimental studies at Eπ+ = 283 MeV (1996BO09, 1999BO25, 2000BO38, 2000GR28, 2005GR28), Eπ- = 292 MeV (1991RA08), Eπ- = 408 MeV/c (2000ST31) and Eπ- = 750 MeV/c (2003ST28) have analyzed the nuclear medium effect on the π-π system. See also (2001CA53).
At En = 59.6 MeV (1982BR04) have determined the angular distribution of the p0 group. The 0° differential cross section to 12Bg.s. at En = 198 MeV has been measured; its ratio to that for the H(n, p) reaction, R, is 0.180 ± 0.006 (1988JA01). The angular distribution of the Jπ = 4- 12B*(4.52) 1p-1h "stretched" state was studied at En = 300 MeV (1993PO05). See (1991BR10: En = 60 and 65 MeV) for analysis of cross sections to 12B*(0, 0.95, 4.4, 7.7) and a comparison of the lowest 1+ and 2+ states populated in 12C(n, p), (p, p) and (p, n) reactions; see also (1990MI10: En = 280 MeV), (2000DA22: En = 98 MeV) and measurements reported in (1975AJ02, 1980AJ01, 1990AJ01). At En = 60 to 260 MeV, differential cross sections were analyzed for data up to Ex ≈ 40 MeV; results on ground state population are analyzed to determine the volume integral of the spin-isospin term of the effective N-N interaction (1992SO02), while the Giant Dipole strength is analyzed via DWIA analysis (1993YA11). A similar review article describing measurements at En = 98 MeV gives additional details on the dipole and spin-dipole strength distributions (1993OL03, 1996OL01). Results from an En = threshold to 10 GeV white source activation experiment are given in (2014ZU03, 2016ZU01). See also (2002KL14, 2008SU21).
This reaction has been measured at Ed = 55 to 270 MeV; see 12.12 (in PDF or PS). The θ ≈ 0° cross section for population of 12Bg.s. is evaluated to analyze the correlation with the Gamow-Teller matrix element for β-decay transitions (1993OH01, 2002RA12). At Epol. d = 270 MeV the state at Ex = 7.5 MeV is dominated by Jπ = 2- strength, while Jπ = 0- is supported for a peak at Ex = 9.3 MeV (1996SA11, 2002OK02). To resolve uncertainty of the 12B*(7.7 MeV) state character, 12B* states were populated using 200 MeV deuterons (1998IN02); the decay neutrons were detected in coincidence with the 2He ejectiles. Analysis of the neutron angular distributions confirm the Jπ = 1- character of 12B*(7.7 MeV). Subsequent studies at Epol. d = 170 MeV measured the angular distributions of cross section and analyzing powers for structures up to Ex < 11 MeV and analyzed the isovector spin-dipole resonance strength distribution; Jπ = 0-, 1- and 2- strength that was observed near Ex = 4.0 and 9.3 MeV, Ex = 7.85 MeV, and Ex = 4.5 and 7.5 MeV, respectively. Further analysis decomposes the structures around 4.4 MeV with Ex = 4.21 ± 0.01 MeV and 4.47 ± 0.01 MeV with Γ ≈ 260 and 209 keV respectively, and indicates Γ ≈ 330 keV for 12B*(9.3), and there is evidence for Jπ = 1- strength at Ex = 10.05 ± 0.08 MeV with Γ ≈ 470 keV (2007DE28, 2008WOZZ). See also (1992SA07, 1999OK02, 1999RU07: theory), and see proton-pair spin correlation studies in (2004HA12, 2004PO03).
This reaction was studied at Et = 129 MeV (2006GU02, 2007GU21), Et = 345 MeV (2006CO14, 2011PE12), Et = 350 MeV (1999SH30) and Et = 381 MeV (1996FU06, 1997DA28, 1998DA05) for θcm(3He) < 10°. Groups are observed at 12B*(0, 2.6, 4.5, 7.3) with Jπ = 1+, 1-, 2-, 1-, respectively. Studies have shown a relation between the σ(θ = 0°) cross sections for Gamow-Teller transitions and the B(GT) value for β-decay transitions such as the 12Bg.s.(1+) to 12Cg.s.(0+) transition; notably (2011PE12) analyzed data for targets up to 120Sn and found a simple relation between the unit cross sections and the target masses for G-T transitions: σ̂GT = 109/A0.65. Discussion in (1999SH30) evaluates the Jπ = 2- spin-flip dipole resonance at Ex = 4.45 MeV, while (1997DA28) finds that the strength near Ex = 7.3 MeV can be separated into a narrower spin-flip component that is populated in (d, 2He) reactions and a broader non-spin-flip component that is populated in (t, 3He) reactions.
At E(7Li) = 82 MeV, a study of the angular distributions for 12B*(0, 0.95, 1.67, 2.62, 4.5, 5.7, 7.6) states deduced that, at this low energy, 2-step processes are dominant (2006SA28). A measurement at E(7Li) = 14 to 26 MeV/A and θ = 0° populated states at 12B*(0, 0.95, 1.67, 2.62, 3.39, 3.76, 4.30, 4.37 4.5, 5.7, (6.2), 7.6); DWBA analysis suggests the reactions proceed via 1-step processes at incident energies above 21 MeV/A (1990NA03, 1990NA24).
Using the spin selectivities of the ΔT = 1 (7Li, 7Beg.s.[Jπ = 3/2-]) and (7Li, 7Be*(0.42[Jπ = 1/2-])γ) reactions the spinflip (ΔS = 1) and non-spinflip (ΔS = 0) components of the cross sections are analyzed at E(7Li) = 26 MeV; the peak at ≈ 4.5 MeV is attributed to Spin Dipole Resonance (SDR) states at 12B*(4.37[Jπ = 2-]) and 12B*(4.52[Jπ = 4-]) while the peak at ≈ 7.6 MeV is attributed to a Jπ = 1- SDR at Ex = 7.6 MeV with Γ = 2.1 MeV and the Giant Dipole Resonance (GDR) at Ex = 7.8 MeV with Γ = 3.2 MeV (1991NA12, 1991NA17, 1994NA17); see also the E(7Li) = 50 MeV/A measurements of (1996JA08, 1999AN13). Further analysis of the E(7Li) = 26 MeV data reveals the GDR at Ex = 7.8 with Γ = 4.0 ± 0.5 MeV (12C*(23.0 ± 0.5 MeV)), the Isovector Giant Monopole Resonance (IVGMR) at Ex = 17.8 ± 1.5 with Γ = 3.5 ± 1.5 MeV (12C*(33 ± 1.5)) and the Isovector Giant Quadrupole Resonance at Ex = 12.8 ± 0.5 MeV with Γ = 3.5 ± 0.5 MeV (12C*(28.0 ± 0.5)) (1992NA13); see also (1987NA16) who found resonances with slightly lower excitation energies. Later studies at E(7Li) = 65 MeV/A (1998NA14, 1998NA16, 1999NA36, 2001NA18) analyzed the θ = 0° cross sections, which are found to be proportional to the GT strengths deduced from β-decay. The reaction is found to be a good spin probe for isovector excitations. See also (1996WI05).
Particle decay spectroscopy was used to reconstruct the excitation energies of 12B T = 2 particle unbound states at Ex = 12.74 ± 0.05 MeV (Γ < 40 keV, Jπ = 0+) and 14.82 ± 0.05 MeV (Γ < 100 keV, Jπ = 2+) (2008CH28). Discussion suggests that the 12B*(12.74) state observed here in the α + 8Li breakup channel is a different state than the one observed in 9Be(7Li, α) (1975AJ03). The 12B*(14.82) state is observed to have breakup cross sections of σ = 522 ± 150, 190 ± 57 and 59 ± 17 μb into the p + 11Be, α + 8Li and 3H + 9Be decay channels, respectively.
This reaction has been studied at energies between 30 and 900 MeV/A, see (1999BO26: E = 357 MeV), (1991AN12: 70 MeV/A), (1994IC01, 1994IC03, 1995IC01: E = 135 MeV/A) and references in (1990AJ01). At E(12C) = 357 MeV states are populated at 12B*(0, 0.95, 1.67, 2.62, 3.39, 4.46[u], 4.52[u], 5.6, 7.4, 8.14, 10.5, 13.4).
Forward-angle differential cross sections have been measured for the groups to 12B*(0, 0.95, 1.67, 4.5[u]); a broad peak near Ex = 7.8 MeV is also populated. The unresolved groups near Ex ≈ 4.5 MeV dominate the spectra, see (1986WI05: 35 MeV/A) and (1999BO26: 30 MeV/A). At E(12C) = 70 MeV/A the Jπ = 0+ → 1+ cross sections, at small angles, were analyzed to determine the correlation between θ ≈ 0° cross section and B(GT) strength (1991AN12); a slight A dependence was observed. At E(12C) = 135 MeV/A the angular distribution for the GT transition to the 12B ground state was analyzed and found to still be dominated by L = 0 components (1994IC01), subsequent analysis of transitions to the Ex = 4.5 and 7.5 MeV states (1994IC03, 1995IC01) indicate the Jπ = 2- and 4- strength for the states near 12B*(4.5) and a dominant Jπ = 2- strength at the 12B*(7.5) Spin Dipole Resonance with some additional Jπ = 0- and 1- strength. See theoretical analysis of the 12B*(0, 0.95) angular distributions in (1999MA18), and see comments on the excitation of the Δ-resonance in (1986BA16, 1988RO1H, 1988RO17: and references therein).
At E(13C) = 29.2 MeV/A and θ ≤ 2° states at 12B*(0, 0.95, 1.67, 2.62, 3.39, 4.46, 7.77) are populated (1988VO06, 1999BO26). The E(13C) = 30 MeV/A differential cross sections at θ = 1.8° are evaluated for the groups to 12B*(0, 0.95, 4.5[u]) and to structures at Ex ≈ 5.5, 7.8, 10.1 and 18.2 MeV (1987AD07); See also (1986VO02, 1988VO08). At E(13C) = 50 MeV/A forward-angle differential cross sections have been measured for θ < 10° for 12B*(0, 0.95, 7.7) (1989BE50, 1993BE19); the GDR peak is located at 7.7 ± 0.1 MeV with Γcm = 1.9 ± 0.1 MeV. The spin transfer selectivity of the Jπ = 1/2- → 1/2- (ΔS = 0, 1, ΔT = 1) 12C(13C, 13N) reaction and the Jπ = 0+ → 1+ (ΔS = ΔT = 1) 12C(12C, 12N) reaction are compared in (1999BO26, 1995IC01); exploiting these two reactions permits the determination of the spin-flip and non-spin-flip isovector excitations. The spin selectivity appears to identify the Ex ≈ 7.5 MeV peak observed in the 12C(12C, 12N) as the Spin Dipole Resonance, while the Ex ≈ 8 MeV peak observed in the 12C(13C, 13N) reaction is identified as the GDR (1995IC01). See also (1999MA18: theory).
The isospin components of the 13C GDR are deduced in (1993MC02) by analyzing the 13C(γ, p)12B*(0, 0.95) data of (1975PA09, 1983ZU02) and the photo-neutron cross section data of (1975PA09, 1977WO04, 1979JU01).
Angular distributions have been measured for the transitions to 12B*(0, 0.95) at Ed = 24.1 to 29 and at 52 MeV; see references in (1980AJ01). Analysis of the 12B*(2.72, 3.76, 5.00) states at Ed = 52 MeV lead to C2S = 1.09 [assuming 1p3/2], 2.17, 0.14, 0.07, 0.22 [assuming 1p1/2] for 12B*(0, 0.95, 2.72, 3.76, 5.00): see (1975MA41). The spectroscopic factors for 12B*(0, 0.95) are S = 1.1 ± 0.2 and 2.0 ± 0.5 (1977LI02). For a summary of information on analog states of 12B and 12C see 12.12 (in PDF or PS) in (1980AJ01).
At Ep = 54 MeV, in addition to transitions to 12B*(0, 0.95, 5.61), the population of T = 2 states at Ex = 12.72 ± 0.07 and 14.82 ± 0.10 MeV is reported. The angular distribution of 3He ions to 12B*(12.75) 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 Γcm ≲ 200 keV (1976AS01).