Source size scaling of fragment production in projectile breakup

Abstract

Fragment production has been studied as a function of the source mass and excitation energy in peripheral collisions of $^{35}$Cl+$^{197}$Au at 43 MeV/nucleon and $^{70}$Ge+$^{nat}$Ti at 35 MeV/nucleon. The results are compared to the Au+Au data at 600 MeV/nucleon obtained by the ALADIN collaboration. A mass scaling, by $A_{source} \sim$ 35 to 190, strongly correlated to excitation energy per nucleon, is presented, suggesting a thermal fragment production mechanism. Comparisons to a standard sequential decay model and the lattice-gas model are made. Fragment emission from a hot, rotating source is unable to reproduce the experimental source size scaling.Comment: 13 pages LaTeX file, including 3 postscript figures (in .tar.gz fornmat), accepted in Phys. Rev. C . Also available at http://thomson.phy.ulaval.ca/ions_lourds/gil-en.htm