251 research outputs found
Fragment properties of fragmenting heavy nuclei produced in central and semi-peripheral collisions
Fragment properties of hot fragmenting sources of similar sizes produced in
central and semi-peripheral collisions are compared in the excitation energy
range 5-10 AMeV. For semi-peripheral collisions a method for selecting compact
quasi-projectiles sources in velocity space similar to those of fused systems
(central collisions) is proposed. The two major results are related to
collective energy. The weak radial collective energy observed for
quasi-projectile sources is shown to originate from thermal pressure only. The
larger fragment multiplicity observed for fused systems and their more
symmetric fragmentation are related to the extra radial collective energy due
to expansion following a compression phase during central collisions. A first
attempt to locate where the different sources break in the phase diagram is
proposed.Comment: 23 pages submitted to NP
Multifragmentation threshold in ^{93}Nb+{nat}Mg collisions at 30 MeV/nucleon
We analyzed the on reaction at 30 MeV/nucleon in the aim
of disentangling binary sequential decay and multifragmentation decay close to
the energy threshold, i.e. MeV/nucleon. Using the backtracing
technique applied to the statistical models GEMINI and SMM we reconstruct
simulated charge, mass and excitation energy distributions and compare them to
the experimental ones. We show that data are better described by SMM than by
GEMINI in agreement with the fact that multifragmentation is responsible for
fragment production at excitation energies around 3 MeV/nucleon.Comment: 16 pages, 12 figures, 5 tables Soumis \`a Nuclear Physics
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
Coulomb chronometry to probe the decay mechanism of hot nuclei
In 129 Xe+ nat Sn central collisions from 8 to 25 MeV/A, the three-fragment
exit channel occurs with a significant cross section. We show that these
fragments arise from two successive binary splittings of a heavy composite
system. The sequence of fragment production is determined. Strong Coulomb
proximity effects are observed in the three-fragment final state. A comparison
with Coulomb trajec-tory calculations shows that the time scale between the
consecutive break-ups decreases with increasing bombarding energy, becoming
quasi-simultaneous above excitation energy E * = 4.00.5 MeV/A. This
transition from sequential to simultaneous break-up was interpreted as the
signature of the onset of multifragmentation for the three-fragment exit
channel in this system.Comment: 12 pages; 13 Figures; 4 Table; Accepted for publication in Physical
Review
N and Z odd-even staggering in Kr + Sn collisions at Fermi energies
The odd-even staggering of the yield of final reaction products has been
studied as a function of proton (Z) and neutron (N) numbers for the collisions
84 Kr+112 Sn and 84 Kr+124 Sn at 35 MeV/nucleon, in a wide range of elements
(up to Z ~ 20). The experimental data show that staggering effects rapidly
decrease with increasing size of the fragments. Moreover the staggering in N is
definitely larger than the one in Z. Similar general features are qualitatively
reproduced by the GEMINI code. Concerning the comparison of the two systems,
the staggering in N is in general rather similar, being slightly larger only
for the lightest fragments produced in the n-rich system. In contrast the
staggering in Z, although smaller than that in N, is sizably larger for the
n-poor system with respect to the n-rich one.Comment: 6 pages, 5 figures, Revtex forma
Long lifetime components in the decay of excited super-heavy nuclei
For nuclear reactions in which super-heavy nuclei can be formed, the essential difference between the fusion process followed by fission and non-equilibrium processes leading to fission-like fragments is there action time. Quite probable non-equilibrium
Response of CsI(Tl) scintillators over a large range in energy and atomic number of ions (Part I): recombination and delta -- electrons
A simple formalism describing the light response of CsI(Tl) to heavy ions,
which quantifies the luminescence and the quenching in terms of the competition
between radiative transitions following the carrier trapping at the Tl
activator sites and the electron-hole recombination, is proposed. The effect of
the delta rays on the scintillation efficiency is for the first time
quantitatively included in a fully consistent way. The light output expression
depends on four parameters determined by a procedure of global fit to
experimental data.Comment: 28 pages, 6 figures, submitted to Nucl. Inst. Meth.
Fission time measurements: a new probe into super-heavy element stability
Accepted for publication in Physical Review LettersReaction mechanism analyses performed with a 4 detector for the systems Pb+Ge, ^{238}10^â18^{208}$Pb+Ge reactions have shorter lifetimes, close to or below the sensitivity limit of the experiment
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