RPA INSTABILITIES IN FINITE NUCLEI AT LOW-DENSITY

Early development of the instabilities in a dilute nuclear source is i nvestigated using a finite temperature quantal RPA approach for differ ent systems, The growth rates of the unstable collective modes are det ermined by solving a dispersion relation, which is obtained by paramet rizing the transition density in terms of its multipole moments. Under typical conditions of a dilute finite system at moderate temperatures the dispersion relation exhibits an ultraviolet cut-off. As a result, only a finite number of multipole modes becomes unstable, and the num ber of the unstable collective modes increases with the size of the so urce. Calculations indicate that for an expanding source, unstable mod es show a transition from surface to volume character. (C) 1997 Publis hed by Elsevier Science B.V.