Eur. Phys. J. A 9, 327-343
Stability and instability of a hot and dilute nuclear droplet
I. Adiabatic isoscalar modes
W. Nörenberg1,2 - G. Papp1,3 - P. Rozmej1,4
1 Gesellschaft für Schwerionenforschung,
D-64291 Darmstadt, Germany
2 Institut für Kernphysik, Technische Universität Darmstadt,
D-64289 Darmstadt, Germany
3 Institut für Theoretische Physik, Universität Heidelberg,
D-69120 Heidelberg, Germany
4 Instytut Fizyki, Uniwersytet Marii Curie-Sk
odowskiej,
Pl-20031 Lublin, Poland
Received: 4 September 2000
Communicated by P. Schuck
Abstract
The diabatic approach to dissipative collective nuclear motion is reformulated in the
local-density approximation in order to treat the normal modes of a
spherical nuclear droplet analytically. In a first application
the adiabatic
isoscalar modes are studied and results for the eigenvalues of
compressional (bulk) and pure surface modes are presented as function of
density and temperature inside the droplet,
as well as for different mass numbers and for
soft and stiff equations of state. We find that the region of bulk
instabilities (spinodal regime) is substantially smaller
for nuclear droplets than for infinite nuclear matter.
For small densities below
30% of normal nuclear matter density and for temperatures below 5 MeV
all relevant bulk modes become unstable with similar growth rates.
The surface modes have a larger spinodal region, reaching out to
densities and temperatures way beyond the spinodal line for bulk
instabilities. Essential experimental features of multifragmentation,
like fragmentation temperatures and
fragment-mass distributions (in particular the power-law behavior)
are consistent with the instability properties of an expanding
nuclear droplet, and hence with a dynamical fragmentation
process within the spinodal regime of bulk and surface modes (spinodal
decomposition).
PACS
21.60.Ev Collective models - 21.65.+f Nuclear matter - 25.70.Mn Projectile and target fragmentation
Copyright Società Italiana di Fisica, Springer-Verlag 2000
