(See Energy Level Diagrams for 9B)
GENERAL: See (1959BA1D, 1960PH1A, 1960SP08, 1960TA1C, 1962BA1C, 1962IN02, 1964GR1J, 1964RE1C, 1964ST1B).
See also Table 9.10 [Table of Energy Levels] (in PDF or PS).
The excitation functions for protons leading to the ground and 2.9 MeV states of 8Be (p0 and p1) have been measured for E(3He) = 0.9 to 17 MeV. Resonances are reported at E(3He) = 1.6 MeV (Γ = 0.25 MeV) and E(3He) = 3.0 MeV (Γ = 1.5 MeV) (1956SC01). Above 5 MeV, the p0-yield at 0° increases monotonically with energy while that of the p1 group decreases with energy. In the backward direction, there is a broad maximum in the yield at ≈ 6.5 MeV (Γ ≈ 4 MeV) (1963MA02). The p0 angular distribution is strongly backward below 7 MeV, and strongly forward at E(3He) = 13 and 17 MeV. At 9 MeV, the p0 distribution is peaked in both the forward and the backward direction (1963MA02).
The yield of neutrons has been determined for E(3He) = 3.0 to 5.5 MeV. It increases linearly with energy above 3.4 MeV: at 5.5 MeV, the cross section is 21.5 ± 2.0 mb (1961FA04).
The ground-state threshold energy is 6.623 ± 0.020 MeV: Q = -3.974 ± 0.012 MeV. Angular distributions at Eα = 8.0, 10.0, 12.0 and 14.0 MeV all display strong forward peaking (1963ME08). At Eα = 14.4 MeV, neutron groups are observed corresponding to the ground and 2.3 MeV states: the upper limit of the cross section to a state at ≈ 1.7 MeV is 100 μb/sr or < 10% of the ground-state group (1964BA29). See also 10B.
At E(3He) = 1.2 to 2.7 MeV, the ground state neutrons and a group corresponding to unresolved 9B*(2.34, 2.81) are observed by time-of-flight, in addition to a continuum distribution. A broad maximum may indicate a level at Ex ≈ 7 MeV (1961DU1B, 1963DU12). The ground state angular distribution has been analyzed in terms of DWBA: L = 2, Jπ ≤ 7/2- is indicated (1963DU12). Analysis of the continuum in terms of plane wave stripping to 8Be + n + p is reported by (1964DU1E).
At E(3He) = 5 to 12.5 MeV, time-of-flight spectra yield evidence for levels at 12.06 ± 0.06, 14.01 ± 0.07, 14.670 ± 0.016, 16.024 ± 0.025, 17.19 and 17.63 MeV. The widths of the four lower states are 800 ± 200, 390 ± 110, < 45 and 180 ± 16 keV, respectively (1964DI1A, 1965DI03). The 14.67 MeV state is the first T = 3/2 state in 9B (1965DI03). It is observed to decay by γ-emission of about equal intensities to the ground and 2.3 MeV states of 9B (1965GR08). See also (1959LE24, 1962SE1A) and 10B.
For Ed = 0.75 to 1.70 MeV, resonances in the yields of protons are observed at 0.900 ± 0.025 MeV (p0, p1) and 1.475 ± 0.010 MeV (p1 only), with Γc.m. = 120 ± 40 and 71 ± 8 keV, respectively (9B* = 17.19 and 17.63 MeV) (1960KA17).
Neutron spectra show a level at 2.37 ± 0.04 MeV (1953AJ09: Ep = 6.59 MeV). Evidence is also reported for states at (1.4), 3.07, 4.14 and 4.93 MeV (1960SA03: Ep = 14.1 MeV), 4.7, 10.3, 11.3, 12.8, 14.7 and 16.6 MeV ((1958AD1A) and C. Waddell; private communication: ± 0.2 MeV; Ep = 31.5 MeV). See also (1961AD02, 1962BO33). At Ep = 6.3 and 7.4 MeV, the upper limit to the cross section for formation of a state at Ex ≈ 1.7 MeV is 100 μb/sr (1964BA29). Angular distributions have been obtained for Ep = 2.0 to 4.3 MeV with special reference to the elucidation of the n - p interaction (1961AL07: see also (1965WA04)). Polarizations and angular distributions of ground-state neutrons have been measured from Ep = 2.4 to 8.5 MeV by (1963KE03, 1963KE09: see also 10B). Angular distributions have also been measured at Ep = 2.3 to 2.6 MeV (1964AN1E), 3.5 to 10.9 MeV (1965WA04: measurement of the polarization for Ep = 7 to 11 MeV), 8 to 14 MeV (1960SA03), 18.5 MeV (1964AN1B). See also (1964SA1D).
For Ep = 2 to 5.8 MeV, two neutron thresholds are observed at Ep = 2.060 ± 0.003 MeV (9B(0)) and 4.645 ± 0.005 MeV (9B* = 2.326 ± 0.006 MeV + 1/2Γ) (1955MA84). A broad threshold is observed at Ep = 3.6 MeV (1955MA84, 1961TA12) but its relevance to a 9B level at ≈ 1.4 MeV is not clear (1959MA20, 1960SP08). An anomaly in the neutron yield curve at Ep = 6.55 ± 0.03 MeV is ascribed to a state in 9B at Ex = 4.04 ± 0.03 MeV (1964BA16).
The width of the ground state is < 2 keV (1951ST76), 540 ± 210 keV; θ2 < 0.25 (1964TE01).
The ground-state tritons are peaked in the forward direction at E(3He) = 4.0 and 4.4 MeV (1963BO1P), 5.7 MeV (1959HI69) and 25 MeV (1960WE04). At the higher energy, only the ground state and the excited state at 2.33 MeV are observed above the continuum up to Ex = 15 MeV; the tritons to the 2.3 MeV state show only weak diffraction maxima (1960WE04). See also (1960TA04, 1962WE1C, 1965CR1C).
Delayed protons are observed corresponding to an excited state of 9B at 12.05 ± 0.2 MeV with Γ = 800 ± 100 keV (1965HA09): see 9C.
At Ep = 18.9 MeV, deuteron groups are observed leading to the ground and 2.3 MeV states (1956RE04). Assuming J = 3/2- and 5/2-, respectively, for these two states the ratio of reduced widths is 1/0.8 (1960MA32). At Ep = 11 MeV, a broad structure is observed which may indicate a level at Ex = 1.6 to 2.0 MeV (1964FA06). At Ep = 155 MeV, deuteron groups are observed corresponding to the ground state and to excited states at 2.4, 7.1, 9.7, 11.4 and 14.7 MeV (1963BA2F). See also (1964SH07).
At Ed = 13.5 MeV, the angular distribution of the ground state tritons can be fitted by PWBA with ln = 1, R = 5.4 fm (1964FU15). See also (1956BO18).
Alpha particle spectra observed with E(3He) up to 10.5 MeV show the ground-state group and groups corresponding to levels at 2.3, 2.8 and 11.6 MeV (Table 9.11 (in PDF or PS)): no other well-defined levels appear for Ex < 10 MeV (1959PO61, 1960SP08, 1960TA12, 1963EA03, 1963FI14). A broad distribution of alpha particles is observed in the region corresponding to Ex = 1.4 MeV, variously interpreted as arising merely from a spatial localization of (8Be + p) with comparatively low disintegration energy (1960SP08), or as an actual 1/2+ level (1962BA1C). In the latter case, the level has Ex ≈ 1.2 MeV, Γ = 1 MeV, γ2p = 1 MeV, R = 4.35 fm; a ground-state reduced width γ2 = ℏ2/ma2 = 2.46 MeV is indicated (1962BA1C).
The ratio of widths for 9B*(2.3)/9Be*(2.4) suggests that both decay by l = 0 or 1 to 8Be*(2+). If Jπ = 5/2- is assumed, the fractional parentage coefficient for (8Be(0) + l = 3) is < 10-3. Comparison of 9B*(2.8)/9Be*(3.0) suggests decay either to 8Be(2+) + l = 0 or 8Be(0) + l = 2 (1960SP08). (1965WA1M) find that the decay of 9B*(2.3) is mainly via 5Li + α, while 9B*(2.8) decays mainly to 8Be(0) + p. The apparent inhibition of 9B*(2.3) → 8Be(0) indicates J ≥ 3/2 (1965WA1M). See also (1964ET02, 1965ET1A).
At Ep = 15.6 and 18.6 MeV, groups are observed leading to the ground and 2.3 MeV states, and angular distributions have been obtained for the ground state alphas (1955RE16, 1962MA40). (1955RE16) does not observe any other sharp groups up to Ex ≈ 7.9 MeV (see also (1958KN52)). The evidence concerning a broad state at Ex ≈ 1.5 MeV is not clear: see (1962SY01, 1964BA29, 1964SY02, 1965IS05). At Ep = 16.0 and 18.3 MeV, α-particles corresponding to an excited state at Ex = 2.9 ± 0.2 MeV have been observed (1964BA29). Stars presumed to arise from the reaction 12C + p → α + 9B → 3α + p have been analyzed in terms of transitions through the 9B ground and 2.3 MeV states (1955NE18, 1962VA1A, 1963VA04: Ep = 29 MeV). See also (1961SE1C).