Excited states in B 11 between 9.5 and 11 MeV were studied by use of the Li 7 (a,y)B u and Li 7 (01,0/) Li 7 * (478 keV) reactions. The thin-target excitation function of the capture reaction, which was obtained at 90° for the ground-state transition from 1.3-to 3.2-MeV bombarding energy, displays a structured peak around 2.5 MeV with a peak differential cross section of 2 /zb/sr. A transition to the first excited state was not observed, setting an upper limit for da/dQ <0.2 jub/sr. By comparing the yield with that of the C 13 (^,Y 0 )N 14 reaction, an absolute peak cross section of 22.5 jub/sr (±20%) was obtained for the 951-keV resonance. Reinvestigation of the inelastic scattering cross section over the same bombarding energy range, coupled with a Breit-Wigner analysis, yielded for the states at 9.87, 10.26, and 10.62 MeV the assignments for spin and parity of f + , i* or § ± , and J + , respectively. This is essentially in agreement with the recent work by Cusson on elastic and inelastic a scattering. Analysis of the radiative capture cross sections (assuming isotropy) with resonance parameters from the particle reactions gives the following ground-state y widths for the established states: <0.5 eV (at 9.88 MeV); 17 eV (10.26 MeV); 1 eV (10.32 MeV); <0.2 eV (10.61 MeV). There is evidence for a new state at 10.45±0.05 MeV with r(c.m.)~140 keV and (2/+l)r 7 =10 eV. Possible analog states in C 11 have been reinvestigated with the B 10 (^,y 0 )C n reaction. The 7 transition strengths observed in B 11 do not agree with present shell-model calculations.
7 transitions to the pair of J*=2+ states at 16.64 and 16.90 MeV in Be 8 have been observed in the reaction Li 7 (i>,Y)Be 8 *-> 2a. The transitions to both states are resonant at the 17.64-and 18.15-MeV states, which have /*= 1 + . The following resonant cross sections and branching ratios have been obtained: 16.90/17.6-> 16.6)= (7±2)%; 16.6)= (50± 10)%.From these transitions and the reported strengths for the transitions from the J T =1 + states to the ground and first excited states, the amount of isospin mixing in the four highly excited states has been determined using intermediate-coupling shell-model wave functions. The squared r=l components amount to 40% and 60% in the 16.6-and 16.9-MeV states, and 95% and 5% in the 17.6-and 18.2-MeV states, respectively. Using these mixing coefficients and the assumption of pure T=0 character for the ground and first excited states, a shell-model calculation accounts approximately for the strengths of most of the observed or reported magnetic dipole transitions from the 17.64-and 18.15-MeV states. Inclusion of a possible J*-1 + , T= 1 level at 19.4 MeV improves the agreement. A large nonresonant transition to the 16.6-MeV state with
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