Total reaction and 2n-removal cross sections of 20–60A MeV ^4,6,8He, ^6–9,11Li, and ¹⁰Be on Si

Total reaction cross sections, σ_R, of 20–60A MeV ^4,6,8He, ^6–9,11Li, and ¹⁰Be were measured by injecting magnetically separated, focused, monoenergetic, identified secondary beams of those projectiles into a Si detector telescope and measuring their energy-deposition spectra. These σ_R’s, accurate to about 3%, were compared with predictions of optical, strong absorption, and microscopic models. The latter gave the best overall fit to the data, providing long-tailed matter densities were assumed. The best available optical potentials generally overpredicted the data by about 10%. Strong absorption calculations, in which the isospin-dependent term is quite important, were often unsuccessful, especially for projectiles with large neutron excess. Two-neutron removal cross sections were measured for ⁶He and ¹¹Li; the ¹¹Li data were slightly overpredicted by a microscopic model which includes correlation effects for the ¹¹Li valence neutrons. Both 2n and 4n removal from ⁸He were observed, in about a 2:1 ratio. Subtraction analysis of the data indicates that ⁴He is a good core within ⁶He and ⁸He, as is ⁹Li within ¹¹Li. © 1996 The American Physical Society.