Heavy-Particle Stripping in theBe9(He3, α)Be8Reaction and Energy Levels ofBe8

Abstract

Angular distributions of alpha particles from the ${\mathrm{Be}}^9({\mathrm{He}}^3, \alpha ){\mathrm{Be}}^8$ reaction leading to the ground state and the levels at 2.9, 16.6, 16.9, and 17.6 MeV were measured at bombarding energies of 3.00 and 4.00 MeV. Reaction alphas were momentum-analyzed with a broad-range spectrograph. Angular distributions for the ground state and the levels at 2.9 and 16.9 MeV are analyzed with a direct reaction theory which includes both the pickup and the heavy-particle stripping amplitudes. Yield measurements for the 17.6-MeV level were not made for angles larger than 100 deg. Over this limited range in angle the angular distributions for this level are in agreement with the predictions of Butler theory. The formation of the 16.6-MeV level apparently proceeds via the compound nucleus. Absolute differential cross sections were found by comparison with the known cross section for the ${\mathrm{Be}}^9(d, p){\mathrm{Be}}^{10}$ reaction. Cross sections for the ${\mathrm{Be}}^9({\mathrm{He}}^3, \alpha ){\mathrm{Be}}^8$ reaction vary from 0.5 mb/sr to 7.6 mb/sr. The level structure of ${\mathrm{Be}}^8$ was studied from the ground state up to 17.6-MeV excitation. Levels were found at excitation energies of 2.90±0.04, 16.633±0.015, 16.928±0.015, and 17.639±0.010 MeV, with the indication of a very broad level in the region of 12.5 MeV. Widths of the 2.9-, 16.6-, and 16.9-MeV levels are 1350±150, 96±20, and 80±15 keV, respectively.