Particle-Particle Correlations: A Tool for Investigating Excited States and Clustering Effects in the Decay of Excited Nuclei

In this contribution we present a selection of results from experiments performed at INFN Laboratori Nazionali di Legnaro exploiting the 4π GARFIELD + RCo apparatus. The investigated reactions are the medium-heavy 32S + 58, 64Ni, and the light 12C + 12C and 14N + 10B systems. For the first set of reactions, we extracted information on fragments in the last but one stage of the compound nucleus decay using particle-particle and fragmentfragment correlation functions. In particular, the issue of odd-even staggering was addressed. We show that the distribution of excited fragments displays odd-even effects, but reversed with respect to the asymptotic distributions. The conclusion is that the staggering cannot be only due to the pairing effect of nuclear masses, but it is also influenced by pairing and possibly isospin effects in the level density. In the light nuclei reactions the possible α-cluster states in even-even nuclei were investigated through particle-particle correlations. Thanks to this powerful technique we were able to reconstruct the particle emission sequence, thus showing that multiple α particle emission from the decay of 24Mg* and 12C* can be understood as a sequential process with an important contribution of doorway Be states. Other chosen applications of the correlation function technique are also briefly reviewed, including measurement of the size, emission time, temperature and symmetry energy of excited nuclear sources.