27 research outputs found
Freeze-out volume in multifragmentation - dynamical simulations
Stochastic mean-field simulations for multifragmenting sources at the same
excitation energy per nucleon have been performed. The freeze-out volume, a
concept which needs to be precisely defined in this dynamical approach, was
shown to increase as a function of three parameters: freeze-out instant,
fragment multiplicity and system size.Comment: Submitted to Eur. Phys. J. A - march 200
Multifragmentation of a very heavy nuclear system (I): Selection of single-source events
A sample of `single-source' events, compatible with the multifragmentation of
very heavy fused systems, are isolated among well-measured 155Gd+natU 36AMeV
reactions by examining the evolution of the kinematics of fragments with Z>=5
as a function of the dissipated energy and loss of memory of the entrance
channel. Single-source events are found to be the result of very central
collisions. Such central collisions may also lead to multiple fragment emission
due to the decay of excited projectile- and target-like nuclei and so-called
`neck' emission, and for this reason the isolation of single-source events is
very difficult. Event-selection criteria based on centrality of collisions, or
on the isotropy of the emitted fragments in each event, are found to be
inefficient to separate the two mechanisms, unless they take into account the
redistribution of fragments' kinetic energies into directions perpendicular to
the beam axis. The selected events are good candidates to look for bulk effects
in the multifragmentation process.Comment: 39 pages including 15 figures; submitted to Nucl. Phys.
Source shape determination with directional fragment-fragment velocity correlations
Correlation functions, constructed from directional projections of the
relative velocities of fragments, are used to determine the shape of the
breakup volume in coordinate space. For central collisions of 129Xe + natSn at
50 MeV per nucleon incident energy, measured with the 4pi multi-detector INDRA
at GSI, a prolate shape aligned along the beam direction with an axis ratio of
1:0.7 is deduced. The sensitivity of the method is discussed in comparison with
conventional fragment-fragment velocity correlations.Comment: 12 pages, 5 figures, subm. to Phys. Lett.