1,942 research outputs found
Experimental signals of the first phase transition of nuclear matter
Vaporized and multifragmenting sources produced in heavy ion collisions at
intermediate energies are good candidates to investigate the phase diagram of
nuclear matter. The properties of highly excited nuclear sources which undergo
a simultaneous disassembly into particles are found to sign the presence of a
gas phase. For heavy nuclear sources produced in the Fermi energy domain, which
undergo a simultaneous disassembly into particles and fragments, a fossil
signal (fragment size correlations) reveals the origin of
multifragmentation:spinodal instabilities which develop in the unstable
coexistence region of the phase diagram of nuclear matter. Studies of
fluctuations give a direct signature of a first order phase transition through
measurements of a negative microcanonical heat capacity.Comment: 9 pages, 5 figures Invited talk to Bologna 2000, Structure od the
Nucleus at the Dawn of the century, Bologna, Italy, May 29 - June 3 2000, to
be published by World Scientifi
LIGHT FRAGMENT EMISSION AND MULTIFRAGMENTATION ?
Light fragments have been observed as a new class of products from heavy-ion collisions at intermediate energies. Two mechanisms which produce such light fragments are well understood but is seems difficult to characterize a third one identified within a moving source framework. From a large set of inclusive data, a few features are extracted and eventual signatures of a multifragmentation process are discussed
Isospin diffusion in semi-peripheral + collisions at intermediate energies (II): Dynamical simulations
We study isospin effects in semi-peripheral collisions above the Fermi energy
by considering the symmetric + and the asymmetric reactions
+ over the incident energy range 52-74 A MeV. A
microscopic transport model with two different parameterizations of the
symmetry energy term is used to investigate the isotopic content of
pre-equilibrium emission and the N/Z diffusion process. Simulations are also
compared to experimental data obtained with the INDRA array and bring
information on the degree of isospin equilibration observed in Ni + Au
collisions. A better overall agreement between data and simulations is obtained
when using a symmetry term which linearly increases with nuclear density
Comparison of fragment partitions production in peripheral and central collisions
Ensembles of single-source events, produced in peripheral and central
collisions and correponding respectively to quasi-projectile and quasi-fusion
sources, are analyzed. After selections on fragment kinematic properties,
excitation energies of the sources are derived using the calorimetric method
and the mean behaviour of fragments of the two ensembles are compared.
Differences observed in their partitions, especially the charge asymmetry, can
be related to collective energy deposited in the systems during the collisions.Comment: 7 pages, 2 figures, presented at the International Workshop on
Multifragmentation and Related Topics, Caen France, 4-7th november 2007
(IWM2007
What Can be Learned Studying the Distribution of the Biggest Fragment ?
In the canonical formalism of statistical physics, a signature of a first
order phase transition for finite systems is the bimodal distribution of an
order parameter. Previous thermodynamical studies of nuclear sources produced
in heavy-ion collisions provide information which support the existence of a
phase transition in those finite nuclear systems. Some results suggest that the
observable Z1 (charge of the biggest fragment) can be considered as a reliable
order parameter of the transition. This talk will show how from peripheral
collisions studied with the INDRA detector at GSI we can obtain this bimodal
behaviour of Z1. Getting rid of the entrance channel effects and under the
constraint of an equiprobable distribution of excitation energy (E*), we use
the canonical description of a phase transition to link this bimodal behaviour
with the residual convexity of the entropy. Theoretical (with and without phase
transition) and experimental Z1-E* correlations are compared. This comparison
allows us to rule out the case without transition. Moreover that quantitative
comparison provides us with information about the coexistence region in the
Z1-E* plane which is in good agreement with that obtained with the signal of
abnormal uctuations of configurational energy (microcanonical negative heat
capacity).Comment: 8 page
Break-up fragments excitation and the freeze-out volume
We investigate, in microcanonical multifragmentation models, the influence of
the amount of energy dissipated in break-up fragments excitation on freeze-out
volume determination. Assuming a limiting temperature decreasing with nuclear
mass, we obtain for the Xe+Sn at 32 MeV/nucleon reaction [J. D. Frankland et
al., Nucl. Phys. A689, 905 (2001); A689, 940 (2001)] a freeze-out volume almost
half the one deduced using a constant limiting temperature.Comment: 11 pages, 6 figure
Kinetic energy spectra for fragments and break-up density in multifragmentation
We investigate the possibility, in nuclear fragmentation, to extract
information on nuclear density at break-up from fragment kinetic energy spectra
using a simultaneous scenario for fragment emission. The conclusions we derive
are different from the recently published results of Viola et al. [Phys. Rev.
Lett. 93, (2004), 132701] assuming a sequential fragment emission and claiming
that the experimentally observed decrease of peak centroids for kinetic energy
spectra of fragments with increasing bombarding energy is due to a monotonic
decrease of the break-up density.Comment: 6 pages, 3 figure
Hanches – La Butte de Gallardon
Le Service archéologie préventive du Conseil départemental d’Eure-et-Loir a conduit, les 4 et 5 avril 2017, un diagnostic archéologique, préalablement à la réalisation de la liaison routière entre la RD 328-10 et la RD 328, sur la commune de Hanches (Eure-et-Loir). Les terrains diagnostiqués, d’une superficie de 8 936 m2, forment une bande linéaire est-ouest, au sommet de l’interfluve sis entre les vallées de la Drouette, au nord, et de la Voise, au sud. Cette opération a permis d’identifier ..
- …