Reducibility and a new entropic term in multifragment charge distributions

The charge distributions and their dependence on fragment multiplicity have been studied for the multifragmentation of 30 MeV/nucleon Xe1Au, Cu. For both targets, the charge distributions are approximately independent of the fragment multiplicity n. However, a residual systematic dependence on n is detectable at the largest values of the total charge multiplicity Nc . Such n dependence obeys a simple scaling law and suggests the presence of an entropic term possibly related to the mechanism of multifragmentation. Thermal scaling between the different bins of Nc seems to occur. PACS number~s!: 25.70.Pq In the multifragmentation of Ar1Au at 110 MeV/nucleon @1# the fragment multiplicity distribution Pn , at any given event transverse energy Et5(Eisin 2 qi , was shown to be reducible to an elementary one-fragment emission probability p by means of the well known binomial equation. It was also noticed that the logarithm of the extracted p depends linearly on 1/AEt ~Arrhenius plot!. These empirical observations were confirmed at other energies and for other systems @2#. Binomial reducibility permits the reconstruction of the probability of an n-fragment event in terms of a binomial combination of a fixed one-fragment probability, and suggests that the fragments are emitted independently with constant probability p. The linearity of the Arrhenius plots in turn suggests that the probability p has a Boltzmann-like thermal dependence: