
^{12}B (2017KE05)(See 12.5 (in PDF or PS) and Energy Level Diagrams for ^{12}B and Isobar Diagram)
Q = 1.32 ± 0.03 fm^{2} (1993OH05). See also 1.34 ± 0.14 fm^{2} (1978MI19). < r^{2}_{matter} >^{1/2} ≈ 2.31  2.35 fm; i.e., see (1988TA10, 2010LI18, 2014ES07).
The halflife of ^{12}B is 20.20 ± 0.02 ms (1978AL01); earlier values are reported in (1968AJ02). ^{12}B decays to ^{12}C*(0, 4.4, 7.7, 10.3, 12.7); states in ^{12}C above E_{x} = 7366 keV are unbound to αdecay: see details in 12.24 (in PDF or PS). The transitions to ^{12}C_{g.s.}[J^{π} = 0^{+}] and ^{12}C*(4.4[J^{π} = 2^{+}]) are allowed; hence the J^{π} of ^{12}B_{g.s.} is 1^{+}. Values of the magnetic dipole moment, μ = 1.0002 ± 0.0028 μ_{N} (2003ZH32), μ = 1.003 ± 0.001 μ_{N} (1997MA21) and μ = 1.001 ± 0.017 μ_{N} (2010ZH03), were measured using βNMR techniques, and the (electric) quadrupole moment, Q = 13.22 ± 0.26 mb (1993MI36, 1993OH05, 1994OH03) was measured using βNQR techniques; these compare well with the presently adopted values: see (2016ST14). A βLevel Mixing Resonance method, which simultaneously gives information on the nuclear alignment, μ and Q values, is applied to ^{12}B in (1997NE01, 1999CO09, 2001CO09). See other theoretical work in (1993KI05, 1993KI22, 2012YU07, 2014RA17), and see discussion on methods for polarizing ^{12}B in (1984KO25, 1985DE54, 1990NO14, 1993SH37, 1997CO15, 1997MA21, 1998MA27, 1999MA24, 2002MO44, 2004NA37, 2007GR23) and references cited in (1985AJ01, 1990AJ01). See discussion on using TiO_{2} (2001OG12, 2002OG08) and superfluid ^{4}He (1995SH22, 1996TA12, 1997TA13) as nuclear spin dewars. Quadrupole coupling constants of polarized ^{12}B in Mg and Zn were measured in (1993OH11). The Gparity irregular induced tensor coefficient in the weak nucleon axial vector current 2Mf_{T}/f_{A} = 0.21 ± 0.09 (stat.) ± 0.07 (sys.) ± 0.05 (theory) (2002MI03) was deduced from the alignment correlation terms in spin aligned ^{12}B and ^{12}N decay. When combined with reanalyzed results from (1998MI14, 1999MI41, 2000MI11) the new analysis gives 2Mf_{T}/f_{A} = 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 ^{12}B and ^{12}N 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 "inmedium" nucleon mass reduction of ≈ (16 ± 4)% (2002MI01). See also (2003SM02). The β^{} spectral shape following ^{12}B decay was measured (1987NA08, 1990CA10, 2000ST19) and compared with the β^{+} spectral shape following ^{12}N 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(^{14}C) = 17.1 MeV/A , ^{12}B states at E_{x} = 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 ^{12}B*(5612) J^{π} = 3^{+} state (2014WU10).
Eleven groups of protons are reported to the known states at E_{x} ≤ 5.6 MeV (1959MO12). Angular distributions have been measured at E(^{6}Li) = 3.5 to 5.95 MeV. The distributions are generally featureless.
Angular distributions have been measured at E(^{7}Li) = 2.10 to 5.75 MeV (1969CA1A: d_{0}, d_{1}, d_{2}, d_{3+4}). The γdecay of the first four excited states has been studied by (1963CA09): ^{12}B*(0.95) decays to the ground state. So, primarily, do ^{12}B*(1.67) [> 98%] and ^{12}B*(2.72) [> 80%], while ^{12}B*(2.62) decays [> 90%] via ^{12}B*(0.95, 1.67). See also 12.7 (in PDF or PS) in (1975AJ02). The mean lifetimes of ^{12}B*(0.95, 2.62) are 295 ± 37 fsec and <48 fsec, respectively (1969TH01). At E(^{7}Li) = 58 MeV the ^{7}Li(^{7}Li, ^{12}B*) → (^{9}Be + t and ^{8}Li + 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).
At E(^{9}Be) = 70 MeV αcluster states at ^{12}B*(10.9, 11.6, 13.4, 14.1, 15.7, 17.4) were observed in the α + ^{8}Li_{g.s.} breakup channel (2004SO19); see also reaction 10.
Reaction cross sections have been measured at E_{cm} = 0.6 to 2.7 MeV (2004HA54, 2006IS04), E_{cm} = 0.6 to 5 MeV (2016DE02), E_{cm} = 0.64 to 2.2 MeV (1995GU02), E_{cm} = 0.9 to 2.8 MeV (2004MI34), E_{cm} = 1.05 MeV (2008LA08, 2010LA07), E_{cm} = 1.25 MeV, E_{cm} = 1.5 to 7 MeV (2000MI34) and E(^{8}Li) = 10 to 20 MeV (1992BO06). Various unresolved ^{12}B resonances are observed. Rates for the reaction path ^{8}Li(α, n)^{11}B(n, γ)^{12}B(β^{})^{12}C are crucial for computing the formation of A > 12 nuclei in inhomogeneous Big Bang Nucleosynthesis (1992BO06, 1993DE30, 2000MI34, 2004CH22). Early estimates for the ^{8}Li(α, n) reaction rate were based on the inverse reaction, ^{11}B(n, α), which only samples the ^{8}Li(α, n_{0}) rate. The direct measurements indicate the total σ to all ^{11}B excited states is roughly five times larger than the branch that feeds only ^{11}B_{g.s.} (1992BO06). Systematic issues are evident when comparing inclusive (^{8}Li, n) and exclusive (^{8}Li, n + ^{11}B) results: see (2006IS04). A novel experiment approached the issue by impinging a ^{8}Li beam on a ^{4}He gas target that was located inside a zeroenergythreshold 4π ^{3}He proportional counter embedded in a polyethylene moderator (2004CH22, 2008LA08, 2010LA07). See (2000MI34) for branching ratios to n_{0} through n_{9}. Also see discussion in (1990DE21, 1992RA04, 1993OB01, 1994KU28, 1996DE02, 2012CO01, 2012LA20, 2016DE02). The fusion barrier is studied in (2016DE02). Elastic α scattering on ^{8}Li was measured in thick target inverse kinematics by impinging a E_{cm} = 10.2 MeV ^{8}Li on a ^{4}He gas cell and detecting the scattered αparticles (2011TO05, 2012DI22). Broad structures at E_{x} ≈ 13.6, 14.4, and 15.8 MeV dominate the excitation function. The role of ^{9}Li(α, n)^{12}B(β^{})^{12}C in astrophysical processes is evaluated in (2010HO09).
Thirteen resonances have been reported in reaction (a) corresponding to 13.6 < E_{x} < 14.7 MeV: see 12.7 (in PDF or PS). Optical potentials for ^{9}Be + t are analyzed in (2007LI55, 2009PA07, 2015PA10). The yield of 2.12 MeV γrays has been measured for E_{t} = 1.5 to 3.3 MeV, E_{t} = 2.96 to 11.46 MeV (2001GE16), and E(^{9}Be) = 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 γrays (from the (t, αn) reaction). Elastically scattered tritons have been studied for E_{t} = 0.60 to 2.1 MeV and E_{pol. t} = 15 and 17 MeV (also A_{y}). The yields of α_{0} and α_{1} have also been reported for E_{t} = 0.52 to 1.70 MeV: see (1975AJ02). The analyzing powers of the reactions leading to ^{6}He_{g.s.} and ^{6}Li*(0, 3.56) have been measured at E_{pol. t} = 17 MeV. For references see (1985AJ01). See also (1988AJ01).
Observed proton groups, above E_{x} = 7.6 MeV are displayed in 12.8 (in PDF or PS). Early studies of lowlying states were carried out at E_{α} = 21.7 MeV (1951MC57, 1955RA41). The later studies at E_{α} = 29, 35.2 and 39.7 MeV (1994MA05, 1994MA06), E_{α} = 50.29 (1991KU31) and E_{α} = 65 MeV (1991KU10, 1992BO16) evaluated neutron unbound states that can participate in the astrophysically important ^{8}Li(α, n) and ^{9}Li(t, n) reactions. In (1991KU31, 1994MA06) the scattered protons, which determine the ^{12}B excitation energy, are measured in coincidence with neutrons, and the angular distributions of the n_{03}decay neutrons are analyzed to constrain l and J^{π} values. The work of (1994MA06) studies the astrophysical significance of ^{12}B*(10.119 to 11.571) states by considering Γ, Γ_{n03}, Γ_{n}, Γ_{α}, and allowed spin values deduced in their analysis. Of particular importance (1994MA05) find no evidence for a state at E_{x} ≈ 10.6 MeV with Γ ≈ 200 keV that is reported by (1990PA22) and is suggested to dominate the Sfactor. See also unpublished work cited in (1985AJ01).
At E(^{6}Li) = 32 MeV ^{12}B*(0, 0.95, 1.67, 3.38, 3.76) and some unresolved states are populated (1986AS02).
Observed αparticle groups are displayed in 12.9 (in PDF or PS). Angular distributions have been measured at E(^{7}Li) = 3.3 to 6.2 MeV, at 20 MeV and at 30.3 MeV: see (1975AJ02, 1980AJ01). At E(^{7}Li) = 20 MeV 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 lowlying states of ^{12}B. It is suggested that the sharp states of ^{12}B at high excitation energies correspond to states of high angular momenta with cluster configurations. At E(^{7}Li) = 52 MeV states at ^{12}B*(10.9, 11.6, 13.4, (14.1), 15.7, (17.7)) were observed in the complete kinematic reconstruction of 2α + ^{8}Li ejectiles from ^{9}Be(^{7}Li, ^{12}B* → α + ^{8}Li)α reactions (2003SO22, 2003SO29).
Total reaction and interaction cross sections are reported at E(^{12}B) = 54.4 MeV/A on ^{nat}Si (2010LI18), at E(^{12}B) = 64 MeV/A on ^{nat}C (2004SA14), at E(^{12}B) = 67 MeV/A on ^{nat}C (2000SA47), at E(^{12}B) = 790 MeV/A on ^{9}Be, ^{nat}C, ^{27}Al (1988TA10), at E(^{12}B) = 920 MeV/A on ^{12}C (1999BO46), at E(^{12}B) = 930 MeV/A on ^{nat}C (2000CH20), and on Cu (1989SA10). Glauber model analyses suggest R^{matter}_{rms} ≈ 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).
Systematics for ^{12}B and other unstable isotope beam production are measured in, for example, (2000FA06, 2000OZ01, 2007NO13, 2012KW02, 2015MO17).
The cross sections for production of ^{8}Li (reaction (b)) and of ^{11}Be (reaction (a)) have been measured for E_{d} = 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 E_{t} = 10 and 23 MeV: see (1980AJ01). The angular distributions are analyzed in a search for manifestation of a ^{12}B neutron or dineutron halo (2008GA09, 2009GA33). See also (2012GA20: theory).
The thermal neutron capture cross section, σ_{th} = 9.09 ± 0.10 mb, is reported by (2016FI06). This compares with σ_{th} = 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 ^{12}B*(0, 953) with I_{γ} = (70.8 ± 0.5)% and (29.2 ± 0.5)%, respectively. The capture cross section was deduced by measuring the ^{12}B decay activity and shows resonances at E_{n} = 20.8 ± 0.5 keV and at 0.43, 1.03, 1.28 and 1.78 MeV, with Γ_{γ} = 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 crosssection measurements have been reported for E_{n} = 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: E_{n} ≤ 600 MeV) and (2011SU23). For differential cross sections see ^{11}B. Polarization measurements have been carried out at E_{n} = 75 keV to 2.2 MeV [see references in (1980AJ01)]. Results from Rmatrix analysis are displayed in 12.10 (in PDF or PS) (1983KO03). For a discussion of the earlier work see 12.5 (in PDF or PS) in (1980AJ01). See also (1995XI06: theory).
The cross sections for reaction (a) have been measured for E_{n} = 14.7 to 16.9 MeV and those for reaction (b) have been investigated for E_{n} = 12.6 to 20.0 MeV and at 25 and 38 MeV: see (1975AJ02). Reaction (d) was measured for E_{n} = 7.6 to 12.6 MeV (1990PA22, 1991PA26) in an effort to evaluate the inverse ^{8}Li(α, n_{0}) reaction via the detailed balance theorem; a resonance at E_{cm}(res) = 580 keV with Γ_{cm} ≈ 200 keV is reported to dominate the cross section; however such a resonance has not been observed in other studies; see (1994MA06) and ^{12}B reaction ^{8}Li(α, n). Earlier measurements are reported at E_{n} = 14.4 MeV (1979AN18), and at E_{n} = 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 E_{p} = 200 MeV ^{12}B*(0, 0.95, 1.67, 2.62, 3.39, 3.76, 4.30 + 4.52, 5.00, 5.61) are reported: see (1985AJ01).
The ^{12}B nucleus was first identified in the analysis of βdecay species produced using this reaction (1935CR02, 2012TH01). Observed proton groups and γrays are displayed in 12.11 (in PDF or PS). Angular distributions of cross sections to ^{12}B_{g.s.} were measured at E_{d} = 76 to 144 keV (1997YA02, 1997YA08). A study in (2010LE02) analyzed angular distributions for protons leading to ^{12}B*(0, 0.95, 1.67, 2.62, 3.39, 4.30); revised spectroscopic factors were deduced for ^{12}B*(3.39, 4.30) and a partial width of Γ_{n}/Γ_{γ} = 95 ± 5 was obtained for ^{12}B*(3.39); implications on the ^{11}B(n, γ) astrophysical reaction rate are discussed. See also (2012CO01). At E_{d} = 26.3 MeV angular distributions of protons to ^{12}B*(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 J^{π} = 2^{+}, 2^{} and 1^{} assignments for ^{12}B*(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 ^{12}B and in ^{12}C. Earlier work is referenced in 12.13 (in PDF or PS) of (1975AJ02). The ^{11}B + n → ^{12}B*(0, 2.62, 2.73) asymptotic normalization coefficients were deduced from DWBA analysis of angular distribution measurements at E_{d} = 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 ^{11}B(n, γ) reaction at astrophysical energies; see also reaction ^{11}B(n, γ). In (2007GU01), the existing ^{11}B(d, p) data is analyzed to extract ANCs for ^{11}B + n → ^{12}B*(0, 0.95, 1.67); then, using charge symmetry, the ANC for ^{12}N → ^{11}C + p is deduced and used to determine the direct capture component for ^{11}C(p, γ); see also (2010TI04, 2012OK02, 2013TI05) and ^{12}N reaction ^{11}C(p, γ). Cross sections useful for boron depth profile studies were measured at E_{d} = 0.7 to 3.4 MeV (2000EL08: γ_{1,2}), E_{d} = 0.6 to 2 MeV (2006SZ07: p_{0} and p_{1} + γ), E_{d} = 0.9 to 1.2 MeV (2009KO09: p_{0}).
At E(^{7}Li) = 34 MeV angular distributions to ^{12}B*(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).
The cross sections for ^{12}B*(0.95, 1.67) deexcitation γrays were measured at E_{cm} = 1.4 to 4.4 MeV (1984DA17, 1986CU02).
Observation of 4.44 MeV γrays from ^{12}B_{g.s.} decay to ^{12}C and βdelayed neutrons from ^{12}B* decay to ^{11}B + n provide evidence that at least two ^{12}B states are fed in ^{12}Be decay; however no detailed decay scheme has been experimentally deduced (1994KE06). Using the ^{12}Be halflife, 21.46 ± 0.05 ms (see ^{12}Be 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 spinisospin flip excitation states at ^{12}B*(0, 0.95, 4.5, 7.5, 10, 13) were measured using tagged E_{brem} = 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 E_{x} = 7.5 MeV. Earlier work with E_{γ} = 210 to 381 MeV (1982AR06) measured the total cross section for π^{+} emission and the spectra of the positive pions; the E_{γ} = 381 MeV data show the influence of quasifree pion production and FSI processes. See also DWIA (1990ER03, 1991OD04, 1995DO24), PWIA (2007TR04), Shell Model (1991ER06) and manybody (1992CA16) analyses. At E_{e} = 195 to 205 MeV the π^{+} energy distributions show contributions from ^{12}B*(0, 0.95, ≈ 4.5, 7.0): see (1986SH14, 1988SH36) and references in (1985AJ01). The 2^{} and 4^{} states at E_{x} ≈ 4.5 MeV have been compared with their isobaric analogs in ^{12}C at E_{x} ≈ 19.5 MeV (1980MI08). At E_{e} = 400 MeV, π^{+} with E_{π} = 32 MeV have been studied: double differential cross sections are obtained for the transitions to ^{12}B*(0, 0.95, 1.67), and single differential cross sections to ^{12}B*(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 E_{γ} = 176 to 187 MeV the giant resonance region, as well as some lower groups, has been studied by (1987MIZZ). Nuclear transparency vs. Q^{2} was studied at E_{e} ≈ 5.8 GeV (2007CL04, 2009KA02, 2010QI02). See also (1988SH36, 1997GI13, 2002DI04, 2016LA08). Differential cross sections for photoproduction of two pions were analyzed for E_{γ} = 400 to 460 MeV using a tagged Bremsstrahlung beam (2002ME22); see theoretical analysis in (2003ME32, 2003RO20, 2003VI09, 2003VI11, 2004MU17, 2006SC18).
Strangeness electroproduction 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 ^{12}C(ν_{e}, e^{+})ν̄ (1982MI05, 1992KO07, 1995KO40, 2002JA03, 2005BO44, 2006CO15, 2006CO16, 2011SA04, 2013SO15) and ^{12}C(ν_{μ}, μ^{+})̄ν (1982MI05, 1995KO40, 1996EN06, 1996KO03, 2002JA03, 2008IV01, 2011KI06, 2014KI06, 2014PA06, 2016PA43). See also ^{12}N reactions 9 and 10 for more discussion.
Observations of γtransitions have led to the determination of the capture rates to ^{12}B*(0[J^{π} = 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 ^{12}C + 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 ^{12}B_{g.s.}, P_{ave}, and of the longitudinal polarization, P_{L}, has been determined by (1981RO05, 1981RO15, 1982RO13): this ratio leads to a neutrino helicity, h_{ν} = 1.06 ± 0.11 (1981RO15), in agreement with the partial conservation of axialvector current (PCAC) hypothesis. The polarization of ^{12}B has also been directly measured by (1984KU20): P_{ave} 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, g_{p}/g_{a} = 10.1^{+2.4}_{2.6}, which is consistent with the prediction of ≈ 7 from Parity Conserved Axialvector Current (1984KU20). See earlier measurements of P_{ave} and P_{L} in (1974PO05, 1977PO1B, 1979TR05) and (1989KA35, 1994KO27, 2002AU01: theory). The branching ratio for "radiative muon capture" (reaction (b)) is R_{γ} = (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, g_{p}, and measurements on ^{12}C, ^{16}O and ^{40}Ca show strong target dependence for the g_{p}/g_{a} 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 ^{12}B*(0, 4.4, 7.9) (1970BI10). Branching ratios have been obtained for these and other unresolved transitions; that to ^{12}B_{g.s.} is (6.22 ± 0.35)% (absolute branching ratio per stopped pion) (1986PE05); see also (1997AM04: theory). The branching ratio for ^{12}C(π^{}, 2γ) is (1.2 ± 0.2) × 10^{5} (1980MA39); see also (1995GI09: theory).
At E_{π} = 165 MeV, excitation of the ^{12}N and ^{12}B isovector analog giant E1 resonances, built on ^{12}C_{g.s.}, is observed (1994HA41). Transitions to the ground states of ^{12}B and ^{12}N, via ^{12}C + π^{∓}, are discussed as a means to understand the difference in ftvalues for ^{12}B and ^{12}N decay to ^{12}C_{g.s.} (1970HI10). Studies of (π^{±}, π^{0}) evaluate the A and isospin dependence of the cross section for the Δnucleus interaction in (1983AS01, 1984AS05, 1990BE41); see also (1987CL02) for a study of delta production at E_{π} = 475 MeV. Analysis of scaling and scaling systems is given in (2013PE24). See (1996NA04) for a measurement with stopped pions.
Experimental studies at E_{π+} = 283 MeV (1996BO09, 1999BO25, 2000BO38, 2000GR28, 2005GR28), E_{π} = 292 MeV (1991RA08), E_{π} = 408 MeV/c (2000ST31) and E_{π} = 750 MeV/c (2003ST28) have analyzed the nuclear medium effect on the π^{}π system. See also (2001CA53).
At E_{n} = 59.6 MeV (1982BR04) have determined the angular distribution of the p_{0} group. The 0° differential cross section to ^{12}B_{g.s.} at E_{n} = 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 J^{π} = 4^{} ^{12}B*(4.52) 1p1h "stretched" state was studied at E_{n} = 300 MeV (1993PO05). See (1991BR10: E_{n} = 60 and 65 MeV) for analysis of cross sections to ^{12}B*(0, 0.95, 4.4, 7.7) and a comparison of the lowest 1^{+} and 2^{+} states populated in ^{12}C(n, p), (p, p) and (p, n) reactions; see also (1990MI10: E_{n} = 280 MeV), (2000DA22: E_{n} = 98 MeV) and measurements reported in (1975AJ02, 1980AJ01, 1990AJ01). At E_{n} = 60 to 260 MeV, differential cross sections were analyzed for data up to E_{x} ≈ 40 MeV; results on ground state population are analyzed to determine the volume integral of the spinisospin term of the effective NN interaction (1992SO02), while the Giant Dipole strength is analyzed via DWIA analysis (1993YA11). A similar review article describing measurements at E_{n} = 98 MeV gives additional details on the dipole and spindipole strength distributions (1993OL03, 1996OL01). Results from an E_{n} = threshold to 10 GeV white source activation experiment are given in (2014ZU03, 2016ZU01). See also (2002KL14, 2008SU21).
This reaction has been measured at E_{d} = 55 to 270 MeV; see 12.12 (in PDF or PS). The θ ≈ 0° cross section for population of ^{12}B_{g.s.} is evaluated to analyze the correlation with the GamowTeller matrix element for βdecay transitions (1993OH01, 2002RA12). At E_{pol. d} = 270 MeV the state at E_{x} = 7.5 MeV is dominated by J^{π} = 2^{} strength, while J^{π} = 0^{} is supported for a peak at E_{x} = 9.3 MeV (1996SA11, 2002OK02). To resolve uncertainty of the ^{12}B*(7.7 MeV) state character, ^{12}B* states were populated using 200 MeV deuterons (1998IN02); the decay neutrons were detected in coincidence with the ^{2}He ejectiles. Analysis of the neutron angular distributions confirm the J^{π} = 1^{} character of ^{12}B*(7.7 MeV). Subsequent studies at E_{pol. d} = 170 MeV measured the angular distributions of cross section and analyzing powers for structures up to E_{x} < 11 MeV and analyzed the isovector spindipole resonance strength distribution; J^{π} = 0^{}, 1^{} and 2^{} strength that was observed near E_{x} = 4.0 and 9.3 MeV, E_{x} = 7.85 MeV, and E_{x} = 4.5 and 7.5 MeV, respectively. Further analysis decomposes the structures around 4.4 MeV with E_{x} = 4.21 ± 0.01 MeV and 4.47 ± 0.01 MeV with Γ ≈ 260 and 209 keV respectively, and indicates Γ ≈ 330 keV for ^{12}B*(9.3), and there is evidence for J^{π} = 1^{} strength at E_{x} = 10.05 ± 0.08 MeV with Γ ≈ 470 keV (2007DE28, 2008WOZZ). See also (1992SA07, 1999OK02, 1999RU07: theory), and see protonpair spin correlation studies in (2004HA12, 2004PO03).
This reaction was studied at E_{t} = 129 MeV (2006GU02, 2007GU21), E_{t} = 345 MeV (2006CO14, 2011PE12), E_{t} = 350 MeV (1999SH30) and E_{t} = 381 MeV (1996FU06, 1997DA28, 1998DA05) for θ_{cm}(^{3}He) < 10°. Groups are observed at ^{12}B*(0, 2.6, 4.5, 7.3) with J^{π} = 1^{+}, 1^{}, 2^{}, 1^{}, respectively. Studies have shown a relation between the σ(θ = 0°) cross sections for GamowTeller transitions and the B(GT) value for βdecay transitions such as the ^{12}B_{g.s.}(1^{+}) to ^{12}C_{g.s.}(0^{+}) transition; notably (2011PE12) analyzed data for targets up to ^{120}Sn and found a simple relation between the unit cross sections and the target masses for GT transitions: σ̂_{GT} = 109/A^{0.65}. Discussion in (1999SH30) evaluates the J^{π} = 2^{} spinflip dipole resonance at E_{x} = 4.45 MeV, while (1997DA28) finds that the strength near E_{x} = 7.3 MeV can be separated into a narrower spinflip component that is populated in (d, ^{2}He) reactions and a broader nonspinflip component that is populated in (t, ^{3}He) reactions.
At E(^{7}Li) = 82 MeV, a study of the angular distributions for ^{12}B*(0, 0.95, 1.67, 2.62, 4.5, 5.7, 7.6) states deduced that, at this low energy, 2step processes are dominant (2006SA28). A measurement at E(^{7}Li) = 14 to 26 MeV/A and θ = 0° populated states at ^{12}B*(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 1step processes at incident energies above 21 MeV/A (1990NA03, 1990NA24). Using the spin selectivities of the ΔT = 1 (^{7}Li, ^{7}Be_{g.s.}[J^{π} = 3/2^{}]) and (^{7}Li, ^{7}Be*(0.42[J^{π} = 1/2^{}])γ) reactions the spinflip (ΔS = 1) and nonspinflip (ΔS = 0) components of the cross sections are analyzed at E(^{7}Li) = 26 MeV; the peak at ≈ 4.5 MeV is attributed to Spin Dipole Resonance (SDR) states at ^{12}B*(4.37[J^{π} = 2^{}]) and ^{12}B*(4.52[J^{π} = 4^{}]) while the peak at ≈ 7.6 MeV is attributed to a J^{π} = 1^{} SDR at E_{x} = 7.6 MeV with Γ = 2.1 MeV and the Giant Dipole Resonance (GDR) at E_{x} = 7.8 MeV with Γ = 3.2 MeV (1991NA12, 1991NA17, 1994NA17); see also the E(^{7}Li) = 50 MeV/A measurements of (1996JA08, 1999AN13). Further analysis of the E(^{7}Li) = 26 MeV data reveals the GDR at E_{x} = 7.8 with Γ = 4.0 ± 0.5 MeV (^{12}C*(23.0 ± 0.5 MeV)), the Isovector Giant Monopole Resonance (IVGMR) at E_{x} = 17.8 ± 1.5 with Γ = 3.5 ± 1.5 MeV (^{12}C*(33 ± 1.5)) and the Isovector Giant Quadrupole Resonance at E_{x} = 12.8 ± 0.5 MeV with Γ = 3.5 ± 0.5 MeV (^{12}C*(28.0 ± 0.5)) (1992NA13); see also (1987NA16) who found resonances with slightly lower excitation energies. Later studies at E(^{7}Li) = 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 βdecay. 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 ^{12}B T = 2 particle unbound states at E_{x} = 12.74 ± 0.05 MeV (Γ < 40 keV, J^{π} = 0^{+}) and 14.82 ± 0.05 MeV (Γ < 100 keV, J^{π} = 2^{+}) (2008CH28). Discussion suggests that the ^{12}B*(12.74) state observed here in the α + ^{8}Li breakup channel is a different state than the one observed in ^{9}Be(^{7}Li, α) (1975AJ03). The ^{12}B*(14.82) state is observed to have breakup cross sections of σ = 522 ± 150, 190 ± 57 and 59 ± 17 μb into the p + ^{11}Be, α + ^{8}Li and ^{3}H + ^{9}Be 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(^{12}C) = 357 MeV states are populated at ^{12}B*(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). Forwardangle differential cross sections have been measured for the groups to ^{12}B*(0, 0.95, 1.67, 4.5[u]); a broad peak near E_{x} = 7.8 MeV is also populated. The unresolved groups near E_{x} ≈ 4.5 MeV dominate the spectra, see (1986WI05: 35 MeV/A) and (1999BO26: 30 MeV/A). At E(^{12}C) = 70 MeV/A the J^{π} = 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(^{12}C) = 135 MeV/A the angular distribution for the GT transition to the ^{12}B ground state was analyzed and found to still be dominated by L = 0 components (1994IC01), subsequent analysis of transitions to the E_{x} = 4.5 and 7.5 MeV states (1994IC03, 1995IC01) indicate the J^{π} = 2^{} and 4^{} strength for the states near ^{12}B*(4.5) and a dominant J^{π} = 2^{} strength at the ^{12}B*(7.5) Spin Dipole Resonance with some additional J^{π} = 0^{} and 1^{} strength. See theoretical analysis of the ^{12}B*(0, 0.95) angular distributions in (1999MA18), and see comments on the excitation of the Δresonance in (1986BA16, 1988RO1H, 1988RO17: and references therein).
At E(^{13}C) = 29.2 MeV/A and θ ≤ 2° states at ^{12}B*(0, 0.95, 1.67, 2.62, 3.39, 4.46, 7.77) are populated (1988VO06, 1999BO26). The E(^{13}C) = 30 MeV/A differential cross sections at θ = 1.8° are evaluated for the groups to ^{12}B*(0, 0.95, 4.5[u]) and to structures at E_{x} ≈ 5.5, 7.8, 10.1 and 18.2 MeV (1987AD07); See also (1986VO02, 1988VO08). At E(^{13}C) = 50 MeV/A forwardangle differential cross sections have been measured for θ < 10° for ^{12}B*(0, 0.95, 7.7) (1989BE50, 1993BE19); the GDR peak is located at 7.7 ± 0.1 MeV with Γ_{cm} = 1.9 ± 0.1 MeV. The spin transfer selectivity of the J^{π} = 1/2^{} → 1/2^{} (ΔS = 0, 1, ΔT = 1) ^{12}C(^{13}C, ^{13}N) reaction and the J^{π} = 0^{+} → 1^{+} (ΔS = ΔT = 1) ^{12}C(^{12}C, ^{12}N) reaction are compared in (1999BO26, 1995IC01); exploiting these two reactions permits the determination of the spinflip and nonspinflip isovector excitations. The spin selectivity appears to identify the E_{x} ≈ 7.5 MeV peak observed in the ^{12}C(^{12}C, ^{12}N) as the Spin Dipole Resonance, while the E_{x} ≈ 8 MeV peak observed in the ^{12}C(^{13}C, ^{13}N) reaction is identified as the GDR (1995IC01). See also (1999MA18: theory).
The isospin components of the ^{13}C GDR are deduced in (1993MC02) by analyzing the ^{13}C(γ, p)^{12}B*(0, 0.95) data of (1975PA09, 1983ZU02) and the photoneutron cross section data of (1975PA09, 1977WO04, 1979JU01).
Angular distributions have been measured for the transitions to ^{12}B*(0, 0.95) at E_{d} = 24.1 to 29 and at 52 MeV; see references in (1980AJ01). Analysis of the ^{12}B*(2.72, 3.76, 5.00) states at E_{d} = 52 MeV lead to C^{2}S = 1.09 [assuming 1p_{3/2}], 2.17, 0.14, 0.07, 0.22 [assuming 1p_{1/2}] for ^{12}B*(0, 0.95, 2.72, 3.76, 5.00): see (1975MA41). The spectroscopic factors for ^{12}B*(0, 0.95) are S = 1.1 ± 0.2 and 2.0 ± 0.5 (1977LI02). For a summary of information on analog states of ^{12}B and ^{12}C see 12.12 (in PDF or PS) in (1980AJ01).
At E_{p} = 54 MeV, in addition to transitions to ^{12}B*(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 ^{3}He ions to ^{12}B*(12.75) is fitted by L = 0; that to ^{12}B*(14.82) is rather featureless [its T = 2 character is assigned from the energies of the analog states]: both states have Γ_{cm} ≲ 200 keV (1976AS01).
