Li-Li azimuthal angular correlations: A test for emission from a rotating source versus instantaneous multifragmentation

Azimuthal angle correlations have been measured for Li-Li pairs from ⁴⁰Ar + ¹⁹⁷Au, ^natAg, ^natCu, ²⁷Al (17A, 27A, and 34A MeV). Many of these correlations exhibit enhancements at Δcphi of 0° and 180°, the classical pattern for evaporation from a hot, high-spin source. A very different pattern is predicted by a simple multifragmentation model, i.e., a peak at Δcphi≊60°. This peak is driven by the rapid Coulomb explosion of a nonrotating nucleus. The latter pattern is not observed experimentally, however, if collective rotation is included in the multifragmentation model, its predictions are more consistent with the observations. Such comparisons can give a promising test for sequential emission from a rotating source versus instantaneous explosive multifragmentation, but one needs a very good selection of collision centrality to reduce the role of the collective rotation. For most of these data the dominant driving forces seem to be rotational motion perturbed by final-state Coulomb repulsions for time delays of the order of 10^-22 s between successive emissions of Li fragments.