(See Energy Level Diagrams for 9B)
GENERAL: References to articles on general properties of 9B published since the previous review (1988AJ01) are grouped into categories and listed, along with brief descriptions of each item, in the General Tables for 9B located on our website at (www.tunl.duke.edu/nucldata/General_Tables/9b.shtml).
The low-lying levels of 9B have mainly  spatial symmetry and thus large amplitudes for breakup into α + α + p. With increasing excitation energy, these states develop large widths making it difficult to identify specific states and the analyses of often rather featureless spectra depend very much on which "known" levels are included in the fit. The relatively narrow states starting, as far as is known, with the 7/2- level at 11.65 MeV, and including the T = 3/2 states, have mainly  spatial symmetry with the T = 1/2 states acquiring their widths through small admixtures of  symmetry. States with  symmetry and L = 1, e.g. the 12.19 MeV level, can have large Gamow-Teller matrix elements for 9C(β+) decay. The analogs of two very narrow positive-parity states of 9Be appear to have been identified near 16.7 and 17.5 MeV in 9B. See reaction 7(a).
The 90° yields of γ0 and of γ to 9B*(2.36) (reaction (a)) have been measured for E(3He) = 0.6 to 1.2 MeV [as have the 2α-particles from the decay of 8Be*(16.6) (reaction (c))]: they are reported to show a resonance at E(3He) = 765 ± 5 keV [9B*(17.111)], attributed to 9B*(17.076) [T = 3/2]. The total cross section for reaction (b) increases monotonically from threshold to ≈ 7 mb at 3.8 MeV. It then decreases monotonically from E(3He) = 5.5 to 7.6 MeV and also from 8.9 to 26.5 MeV: see (1979AJ01, 1984AJ01), and 8B.
Absolute cross sections for protons (reaction (c)) to 8Be*(0, 2.9, 16.6, 16.9) as well as for the continuum protons have been measured for E(3He) = 0.5 to 1.85 MeV. Reaction rate parameters, <σv>, have been calculated for kT = 0.01 to 10.0 MeV. Excitation functions for p0 and p1 have been measured for E(3He) = 0.9 to 17 MeV, and polarization measurements are reported at E(3He) = 14 MeV. Resonances are observed at E(3He) = 1.6 and 3.0 MeV [Γ = 0.25 and 1.5 MeV]: see (1974AJ01, 1979AJ01), and 8Be. Polarization measurements are also reported at E(vec. 6Li) = 21 MeV, and vector analyzing powers for the transition to the ground state of 8Be were measured (1983KO04). Differential cross sections and analyzing powers were measured for E(3He) = 4.6 MeV (1995BA24). In the range E(3He) = 0.7 to 2.0 MeV, a resonance in the excitation function for deuterons (reaction (d)) is reported corresponding to 9B*(17.6). Polarization measurements at E(vec. 3He) = 33.3 MeV for the d0 and d1 groups are reported. Excitation functions for t0 (reaction (e)) have been measured for E(3He) = 10 to 16, and 23.3 to 25.4 MeV: see (1974AJ01). Polarization measurements are reported at E(vec. 3He) = 33.3 MeV for the t0 group as well as for the 3He ions to 6Li*(0, 2.19) (reaction (f)). The decay of 6Be levels populated by reaction (e) for E(3He) = 30.7 - 40 MeV was studied in experiments reported in (1987BO39, 1988BO38, 1989BO42, 1992BO25). The elastic scattering (reaction (f)) has also been studied for E(3He) = 0.7 to 2.0 MeV [see references cited in (1974AJ01, 1979AJ01, 1984AJ01)]. Differential cross section measurements have been reported at E(3He) = 93 MeV (1994DO32), and 50 - 72 MeV (1995BU20). See also the calculations in (1992KA06, 1993SI06) and the analyses in (1995MA57, 1995MI16). The α - α coincidences (5Lig.s. decay) (reaction (g)) have been measured for E(3He) = 1.4 to 1.8 MeV: a resonance is observed at 1.57 ± 0.02 MeV [9B*(17.63)], Γ = 70 ± 20 keV. Polarization measurements of the α-particles to 5Li*(0, 16.7) are reported at E(vec. 3He) = 33.3 MeV. See also the measurements at E(3He) = 1.5 - 3.5 MeV (1988BU04) and at E(3He) = 8 - 14 MeV (1990AR17). Reaction amplitudes for resonance scattering were calculated for E(3He) = 8 - 14 MeV by (1996FA05). For a study of the (3He, pα)4He reaction at 3.5, 4.4 and 5.5 MeV see (1987ZA07). See (1979AJ01, 1984AJ01) for references.
Angular distributions of the t0 group have been measured for E(6Li) = 4.0 to 5.5 MeV and at 7.35 and 9.0 MeV. No evidence was observed for a group corresponding to 9B*(1.6): see (1974AJ01). In an experiment reported in (1995TI06), the relative energy spectrum for 9B → 8Be + p was measured using E(6Li) = 56 MeV. The 2.36 MeV 5/2- state is absent from the spectrum because it decays into 5Li + α. The spectrum can be fitted with the 2.79 MeV 5/2+ state and a broad 1/2- state at an excitation energy of 2.3 - 3.2 MeV. The best fit occurs for an energy of 2.91 MeV and a width of 3.05 MeV, in good agreement with values deduced from an analysis of 9Be(p, n)9B: see reaction 7. The fit can be further improved below 1.5 MeV by adding a small contribution from a 1/2+ level. The reaction mechanism for E(6Li) = 2 - 16 MeV was studied by (1990LE05).
For 3He incident energies up to 12.5 MeV the only clear peaks at low excitation energy correspond to the 9B ground state and the unresolved 9B*(2.4, 2.8) states. A peak has been reported at Ex = 4.8 ± 0.1 MeV [Γ = 1.0 ± 0.2 MeV] in one experiment. At higher excitation, there is evidence for levels with energies (in MeV) and widths [Γ (in MeV) in brackets] at 12.06 ± 0.06 [0.8 ± 0.2], 14.01 ± 0.07 [0.39 ± 0.11], 14.67 ± 0.016 [< 0.045], 16.024 ± 0.025 [0.180 ± 0.016], 17.19 and 17.63 (1965DI03). 9B*(14.66) is the first T = 3/2 state in 9B. Its decay properties are displayed in 9.4 (in PDF or PS) and compared with those of 9Be*(14.40): see reaction 9 in 9Be and (1974AJ01). Angular distributions have been measured at E(3He) = 1.56 to 5.27 MeV: see (1974AJ01).
The cross section for reaction (a) for E(7Be) = 16.9 MeV is 58 ± 11 mb (1983HA17, 1985HA40). The differential cross section was measured at Ecm = 5.8 MeV (1997LI05) in order to obtain the 8B → 7Be + p asymptotic normalization coefficient (ANC), from which the astrophysical S factor for the 7Be(p, γ)8B reaction was deduced. The reaction cross section was calculated for Ecm = 5.8, 15.6, 38.9 MeV (1999FE04). For Ed = 0.75 to 1.70 MeV, resonances in the yields of protons are observed at Ed = 0.900 ± 0.025 MeV (p0, p1) and 1.475 ± 0.010 MeV (p1 only) with Γcm = 120 ± 40 and 71 ± 8 keV, respectively [9B* = 17.19 and 17.64 MeV]: see (1974AJ01). See also (1985CA41; astrophys.).
Experiments on isospin splitting in analog giant resonances excited by single pion charge exchange reactions are reviewed in (1994HA41).
For reaction (a), angular distributions have been reported at many energies in the range Ep = 3.5 to 49.3 MeV [see (1979AJ01, 1984AJ01)] and at 16.44 and 17.57 MeV (1986MU07; n0). The width of the ground state is 0.54 ± 0.21 keV: see (1974AJ01).
At Ep = 135 MeV, excitation energies, widths, and angular distributions have been measured for states up to Ex = 17.54 MeV (1985PU1A). Below Ex = 5 MeV, the dominant excitations are to the ground state and a broad 1/2- state at Ex = 2.75 ± 0.30 MeV [Γ = 3.13 ± 0.20 MeV]. The 2.36 MeV 5/2- state, the 2.788 MeV 5/2+ state, taken at 2.71 ± 0.1 MeV [Γ = 0.7 ± 0.1 MeV], and a new level at 4.3 ± 0.2 MeV [Γ = 1.6 ± 0.2 MeV] are also populated. The 0° cross sections for the 0 and 2.75 MeV states are comparable and the extracted B(GT) values for these states and the 5/2- level agree well with p-shell predictions (1987RA32, 1988MI03). States at Ex = 7.0 ± 0.1 MeV [Γ = 2.0 MeV] and 11.63 ± 0.2 MeV [not broad] are not seen at 0° and have angular distributions consistent with the 7/2- assignments from single-neutron pickup reaction on 10B. The angular distributions for states at Ex = 12.23 ± 0.1 MeV [Γ = 0.5 ± 0.1 MeV], 13.96 ± 0.1 MeV [not broad] and 14.60 ± 0.1 MeV [narrow state plus a broad component with Γ = 0.6 ± 0.1 MeV] are forward peaked with modest B(GT) values. Cross sections for the 0, 2.36, 12.2, 14.0, 14.6 MeV states and two narrow states at Ex = 16.71 ± 0.1 and 17.54 ± 0.1 MeV are compared with shell-model predictions in (1991DI03). The 16.7 and 17.5 MeV states appear to be the analogs of the 16.67 MeV (5/2+) and 17.49 MeV (7/2+) states of 9Be. There is also evidence at some angles for narrow states at 15.15 ± 0.1 MeV, 15.44 ± 0.1 MeV, and 15.86 ± 0.1 MeV (1985PU1A).
Measurements of neutron polarization for Ep = 54 MeV were reported in (1988HE08). See also the cross section measurements at Ep = 35 MeV of (1987OR02). For earlier work see (1974AJ01, 1984AJ01). Quasi-elastic scattering at Ep = 300 - 400 MeV was studied by (1994SA43), and differential cross sections for isobaric analog ΔJπ = 0+ (Fermi-type) transitions were measured at Ep = 35 MeV (2000JO17). See also the analysis and calculations of (1994GA49) for Ep = 1 GeV, and (1998IO03) for pion production at Ep = 800 MeV. A summary of monoenergetic neutron sources for En > 14 MeV is presented in (1990BR24). Application-related measurements are discussed in (1987RA23, 1996SH29).
Reaction (b) does not seem to involve states of 9B. See also (1982GU13, 1983BY02, 1984BA1R, 1987RA32, 1988BO47, 1988HE08) and the application-related work of (1984ALYS, 1987VO1F). For yield and polarization measurements see 10B.
Angular distributions have been measured for E(3He) = 3.0 to 25 MeV and at 217 MeV: see (1974AJ01, 1979AJ01). At E(3He) = 39.8 MeV, 9Bg.s. is strongly populated and 9B*(2.33, 2.83, 11.62, 12.06, 14.67, (17.19), 17.63) are also observed (1969BA06). At E(3He) = 90 MeV triton groups are reported to states at Ex = 1.16 ± 0.05 MeV [Γ = 1.3 ± 0.05 MeV], 2.32 ± 0.03, 2.72 ± 0.04 and 4.8 ± 0.03 MeV [1.5 ± 0.3 MeV], 16.7 ± 0.1 MeV [< 0.1 MeV], 18.6 ± 0.3 and 20.7 ± 0.5 MeV [1.6 ± 0.3 MeV] [Γ in brackets], in addition to known and possibly unresolved 9B*(7.0, 11.7, 12.1, 14.7, 17.64) states (1987KA36). See also (1983DJZV). (2001AK09) have fitted 0°, 2°, and 3.5° spectra at E(3He) = 450 MeV with levels fixed at excitation energies of 0, 2.361, 2.788, 4.8, and 6.97 MeV together with two levels at 1.80+0.22-0.16 and 3.82+0.23-0.22 MeV with widths of 600+300-270 and 1330+620-360 keV; see also (1994AK02) for the excitation of states above Ex = 10 MeV at 0°. Neither (1987KA36) nor (2001AK09) include in their fits the broad 1/2- level that is strongly excited in the 9Be(p, n)9B reaction.
The 9Be(3He, tα)9B reaction with E(3He) = 40.5 MeV has been used to obtain α-decay spectra from the 5/2- level at 2.36 MeV (1990BO51). The data were analyzed in terms of series expansions of the decay amplitudes in hyperspherical harmonics.
At E(6Li) = 32 MeV angular distributions are reported to 9B*(0, 2.36) (1985CO09). Measurements with E(6Li) = 32 MeV are also reported by (1988BU18). In addition to 9B*(0, 2.36) they report weak levels at Ex = 1.32 ± 0.08 MeV, Γ = 0.86 ± 0.26 MeV and Ex = 4.60 ± 0.16 MeV, Γ = 0.68 ± 0.43 MeV. See also (1984GL06; E(6Li) = 93 MeV, E(7Li) = 78 MeV).
The status of evidence for the mirror state of the 1/2+ 1.68 MeV state in 9Be was reviewed (1992CA31), and reinvestigated by 9Be(6Li, 6He)9B measurements with E(6Li) = 32 MeV. They find no evidence for the level. A measurement reported in (1993RE04) with polarized 6Li ions at 32 MeV determined polarization observables for 9B*(0, 2.36). The results were compared to coupled-channels calculations.
The previous review (1988AJ01) notes that 9C β+ decay was observed by (1988MI03) to 9B*(0, 2.36, 2.8) [Jπ = 3/2-, 5/2-, 1/2-] with branching ratios of (60 ± 10), (17 ± 6) and (11 ± 5)%, respectively. A state at Ex = 12.1 ± 0.6 MeV, Γ = 0.4 ± 0.1 MeV was also observed with the remaining strength going to it. In (2000GE09, 2001BE51), the β-delayed particle decay of 9C has been studied and secondary decays into 8B + p and 5Li + α have been observed. In (2001BE51), a value of 54.1 ± 1.5% is reported for the ground-state branch and no asymmetry is found with the corresponding transition in 9Li(β-)9Be. They determine Jπ = 5/2- for the 12.2 MeV level from a study of angular correlations and measure a large B(GT) value for the transition to the 12.2 MeV level. They observe a transition to the isobaric analog state and obtain new information on the decay of this state. In (2000GE09) a number of 9B level energies, branching ratios, and Gamow-Teller strengths were deduced using an R-matrix analysis with simplified one-level expressions. Level energies, branching ratios, B(GT) values, and other decay information obtained by combining the results of (2000GE09) and (2001BE51) are presented in 9.14 (in PDF or PS) and its footnotes. The data of (2000GE09) have also been analyzed using a multichannel, multilevel R-matrix approach and the results are described in (2001BU05). See reaction 12 in 9Be and 9.8 (in PDF or PS) for the mirror decay 9Li(β-)9Be; note the large asymmetry for the decays to the 11.81 MeV level of 9Be and 12.16 MeV level of 9B.
At Ep = 33.6 MeV (1968KU04) and 155.6 MeV (1969BA05) deuteron groups are observed to the states shown in 9.15 (in PDF or PS). All have angular distributions characteristic of ln = 1. Angular distributions are also reported for 9B*(0, 2.36) at Ep = 18.6 MeV (1985BE13).
Angular distributions have been measured at Ed = 11.8 to 28 MeV [see (1974AJ01, 1979AJ01)] and 18 MeV (1988GO02, 1988GU20; to 9B*(0, 2.36)). See also the analysis of cross section data for Ed = 8 - 50 MeV (1995GU22).
Alpha-particle spectra show the excitation of 9B*(0, 2.4, 2.8, 11.8): see (1966LA04). Measurements by (1968KR02) determine Ex = 2.361 ± 0.005 and 2.788 ± 0.030 MeV [Γ = 81 ± 5 and 548 ± 40 keV, respectively]: see 9.11 (in PDF or PS) in (1966LA04) for other values. There is some evidence for a state with Ex ≈ 1.6 MeV, Γ ≈ 0.7 MeV, but it is not conclusive. No evidence is found for any narrow levels in 9B with Γ ≤ 100 keV and 4 < Ex < 7 MeV: the upper limit to the intensity of the corresponding α-group is 1% of the intensity of the group to 9B*(2.4). Angular distributions have been determined at E(3He) = 5.5 and 33.7 MeV [see (1974AJ01)].
In reaction (b), a study of the decays of 9B*(2.4, 2.8) shows that 9B*(2.4) decays < 0.5% by proton emission to 8Beg.s. [it decays to 5Lig.s. by α-emission] while the second state, Ex = 2.71 ± 0.03 MeV [Γ = 0.71 ± 0.06 MeV], decays almost 100% by that channel (1966WI08). No evidence is found for excited states of 9B with 3.5 < Ex < 9.5 MeV which decay by proton emission to 8Beg.s. (1968KR02). In a kinematically complete experiment (reaction (c)) at E(3He) = 2.3 and 5.0 MeV, a state is reported at 4.9 ± 0.2 MeV with a width of 1.5 ± 0.3 MeV (1986AR14). Likewise, from reactions (b) and (c) a state is reported at 1.8 ± 0.2 MeV with a width of 0.9 ± 0.3 MeV (1988AR05).
At Ep = 45 MeV angular distributions have been obtained for the triton groups to 9B*(0, 2.36, 12.06, 14.01, 14.66, 16.02). In addition the spectra show some indication of the groups corresponding to 9B*(7.0, 17.19, 17.64). T = 1/2 states are reported at Ex = 15.29 ± 0.04 and 15.58 ± 0.04 MeV (1971HA10). The first two T = 3/2 states have been observed at Ex = 14.6550 ± 0.0025 (1974KA15) and 17.076 ± 0.004 MeV [Γ = 22 ± 5 keV] (1974BE66).
Angular distributions have been measured at Ep = 14.0 to 54.1 MeV [see (1974AJ01)]. At Ep = 54.1 MeV peaks are observed at 0, 2.32 ± 0.04, 6.97 ± 0.06, and 11.46 ± 0.25 MeV (1971MA2C). The angular distribution for the 6.97 MeV state is similar to other J = 7/2 transitions (1972MA21). At Ep = 42.8 MeV angular distributions for 9B*(0, 2.36, 6.98) involve l = 1, 3 and 3, respectively (1983PE07). A broad state at 2.9 ± 0.2 MeV has also been reported: see (1974AJ01). Angular distributions involving the α0 and α* groups [to 4He*(20.1), 0+] to 9Bg.s. have been studied at Ep = 42 MeV: see (1984AJ01). For reaction (c) see (1985DE17; Ep = 58 MeV). See also (1984AJ01, 1988AJ01).
Differential cross sections were measured for reaction (a) at Et = 38 MeV and for reaction (b) at E(3He) = 33 MeV by (1989SI02). Spectroscopic factors for cluster pickup were extracted. A reanalysis of the data for reaction (a) is presented in (1992CL04). Spectroscopic factors are compared with shell model and microscopic calculations. In other work on reaction (b) angular distributions were studied at E(3He) = 30.0 and 40.7 MeV [see (1974AJ01)] and at E(3He) = 33.4 MeV (1986CL1B; to 9B*(0, 2.36), and cross sections for 9B*(0, 2.36, 2.78, 6.97, 11.7) were measured by (1993MA48). Spectroscopic factors for 3H pickup were extracted and compared with shell-model predictions. See also the analysis in (1995MA57).