Search for emission of unstable ${}^8$Be clusters from hot ${}^{4}0$Ca and ${}^{5}6$Ni nuclei

Abstract

The possible occurence of highly deformed configurations is investigated in the ${}^{40}$Ca and ${}^{56}$Ni di-nuclear systems as formed in the ${}^{28}$Si + ${}^{12}$C and ${}^{28}$Si + ${}^{28}$Si reactions, respectively, by using the properties of emitted light charged particles. Inclusive as well as exclusive data of the heavy fragments (A $\ge$ 6) and their associated light charged particles (p, d, t, and $\hat{I}\pm$-particles) have been collected at the IReS Strasbourg VIVITRON Tandem facility with two bombarding energies $E_{lab}{(}^{28}$Si) = 112 and 180 MeV by using the ICARE charged particle multidetector array, which consists of nearly 40 telescopes. The measured energy spectra, velocity distributions, in-plane and out-of-plane angular correlations are analysed by Monte Carlo CASCADE statistical-model calculations using a consistent set of parameters with spin-dependent level densities. Although significant deformation effects at high spin are needed, the remaining disagreement observed in the ${}^{28}$Si + ${}^{12}$C reaction for the S evaporation residue suggests an unexpected large unstable ${}^8$Be cluster emission of a binary nature.

13 pages latex, 9 eps figures. Paper presented at the XXXIX International Winter Meeting on Nuclear Physics, Bormio(Italy) January 22-27, 2001 (to be published at Ricerca Scientifica ed Educazione Permanente)