- th / 0 10 20 08 v 1 5 F eb 2 00 1 Statistical evolution of fragment ’ s isospin in nuclear
نویسنده
چکیده
The two instructive effects concerning fragment production at disintegration of finite nuclei are predicted with the statistical multi-fragmentation model: (1) a concentration of neutrons in intermediate mass fragments during the phase transition, (2) the break of the spatial symmetry of the fragment's isospin distribution, as well as of the symmetry of the fragment's emission from a statistical source, induced by the external Coulomb field. The knowledge of the isotope composition of fragments produced in nuclear multifragmentation can help in resolving the important problems: Do the fragments keep memory about the initial dynamical stage or they have statistical origin? How the isospin influences disintegration of finite nuclei and what is the difference from the case of nuclear matter? What is the isospin dependence of the nuclear equation of state? Generally, this study addresses an intriguing interdisciplinary problem of the phase transition in a finite-size two-component system (i.e. in a nucleus consisting of neutrons and protons), that is instructive for all fields dealing with finite systems. The problem was investigated within the statistical multifragmentation model (SMM) [1], which is successfully used for explanation of experimental data. A new Markov chain method of partition generation was incorporated in the model [2], that allows for considering the multifragmentation process on a solid microcanonical basis. The presented results reflect statistical properties of the fragment production and can be used for identification of the phenomenon. Presently, one of the extensively discussed topics is the isospin fraction-ation at disintegration of excited nuclei [3]. Fig. 1 shows mass distributions and neutron-to-proton ratios (N/Z) of the fragments produced after multi-fragmentation of a Au source (mass number A s =197, charge Z s =79), the 1
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تاریخ انتشار 2001