The Critical Exponent of Nuclear Fragmentation

A. BARRA~NON; R. CARDENAS; C.O. DORSO; J.A. LOPEZ

ACTA PHYSICA HUNGARICA. HEAVY ION PHYSICS

Año: 2003 vol. 17 p. 59 - 73

1219-7580

Abstract. Nuclei colliding at energies in the MeV's break into fragments in aprocess that resembles a liquid-to-gas phase transition of the excited nuclearmatter. If this is the case, phase changes occurring near the critical pointshould yield a \droplet" mass distribution of the form A􀀀 , with  (a criticalexponent universal to many processes) within 2    3. This critical phenomenon,however, can be obscured by the niteness in space of the nuclei andin time of the reaction. With this in mind, this work studies the possibility ofhaving critical phenomena in small \static" systems (using percolation of cubicand spherical grids), and on small \dynamic" systems (using molecular dynamicssimulations of nuclear collisions in two and three dimensions). This is doneinvestigating the mass distributions produced by these models and extractingvalues of critical exponents. The specic conclusion is that the obtained valuesof  are within the range expected for critical phenomena, i.e. around 2:3, andthe grander conclusion is that phase changes and critical phenomena appearto be possible in small and fast breaking systems, such as in collisions betweenheavy ions.