Evolution of fragment-fragment correlations in reactions of 197Au and 107,109Ag with 40Ar from 7A to 34A MeV.

Abstract

In-plane and out-of-plane angular correlations have been measured between fragments of Z>3, Li fragments, $^{3,4}\mathrm{He}$, and $^{1,2,3}\mathrm{H}$. The changing patterns for $^{40}\mathrm{Ar}$ induced reactions of 7A, 17A, 27A, and 34A MeV give an overview of the decreasing importance of mass-symmetric fissionlike reactions at the expense of a broad range of more mass-asymmetric breakups. Evidence is given that these fragments come from a central collision group of reactions that have similar violence and from which many combinations of fragments and particles are ejected. Very similar azimuthal angular correlations are observed for particles with a Li fragment and for particles with a pair of heavier fragments (Z>3). This similarity suggests comparable strengths of association with the reaction plane for single Li fragments and for fragment pairs of Z>3. Azimuthal angular correlations for Li-Li pairs exhibit distinct asymmetries; their interpretation via trajectory-model calculations indicates mean delay times of \ensuremath{\approxeq}5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}22}$ s.