Multifragmentation of a very heavy nuclear system (I): selection of single-source events

Frankland, J.D.; Bacri, C.O.; Borderie, B.; Rivet, M. F.; Squalli, M.; Auger, G.; Bellaize, N.; Bocage, F.; Bougault, R.; Brou, R.; Buchet, P.; Chbihi, A.; Colin, J.; Cussol, D.; Dayras, R.; Demeyer, A.; Doré, D.; Durand, Dominique; Galichet, E.; Genouin-Duhamel, E.; Gerlic, E.; Guinet, D.; Lautesse, P.; Laville, J.L.; Lecolley, J.F.; Légrain, R.; Neindre, N. Le; Lopez, O.; Louvel, M.; Maskay, A. M.; Nalpas, L.; Nguyen, A.D.; Pârlog, M.; Péter, J.; Plagnol, E.; Rosato, E.; Saint‐Laurent, F.; Salou, S.; Steckmeyer, J.C.; Stern, M.; Tăbăcaru, G.; Tamain, B.; Tirel, O.; Tassan‐Got, L.; Vient, E.; Volant, C.; Wieleczko, J. P.

doi:10.1016/s0375-9474(00)00606-0

Cited by 52 publications

(53 citation statements)

References 54 publications

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“…Fused systems produced in central collisions between heavy nuclei allow to address rather large pieces of nuclear matter, of about 200-400 nucleons which undergo multifragmentation [8,9]. The present paper, presenting intra-event correlations which are highly enlightening for the origin and the features of the process, enlarges and completes the comparison started in reference [9].…”

Section: Introductionsupporting

confidence: 57%

Multifragmentation of very heavy nuclear systems (III): Fragment velocity correlations and event topology at freeze-out

et al. 2006

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Kinetic energy spectra and fragment velocity correlations, simulated by means of stochastic mean-field calculations, are successfully confronted with experimental data for single multifragmenting sources prepared at the same excitation energy per nucleon in 32 AMeV 129 Xe+ nat Sn and 36 AMeV 155 Gd+ nat U central collisions. Relying thus on simulations, average freeze-out times of 200-240 fm/c are estimated The corresponding spatial distributions of fragments are more compact for the lighter system (∼3-4V 0 vs ∼8V 0 ).

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Section: Introductionsupporting

confidence: 57%

Multifragmentation of very heavy nuclear systems (III): Fragment velocity correlations and event topology at freeze-out

et al. 2006

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“…This is in qualitative agreement with the trend observed in central collisions at relativistic energies [13]. On the other side up to 10% transparency the distributions are almost identical, meaning that when the velocity difference between the quasi-projectile and the quasi-target is of this order, the debate on equilibrium based on the number of emis-sion sources [14] is an academic question. The important influence of the collective component on the cluster distributions means that, if the incoming momentum is not completely relaxed, the methods used to determine thermodynamical quantities can be strongly biased.…”

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confidence: 86%

“…Since a negative heat capacity corresponds to abnormally high partial energy fluctuations [8], Figure 2 implies that an incomplete relaxation of the incoming momentum can prevent the observation of negative heat capacity. Another important form of collective motion in heavy ion collisions is radial flow which starts to be observed in central collisions around 30 A.MeV incident energy [14] and becomes the dominant fraction of the detected energy in the relativistic domain [13]. We can describe this dynamical situation in the framework of information theory as an equilibrium with non random directions for velocities which are preferentially oriented in the radial direction.…”

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confidence: 99%

Equilibrium under flow

Gulminelli

Chomaz

2004

Nuclear Physics A

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Using information theory we derive a thermodynamics for systems evolving under a collective motion, i.e. under a time-odd constraint. An illustration within the Lattice gas Model is given for two model cases: a collision between two complex particles leading to a incomplete relaxation of the incoming momentum, and a self-similar expansion. A semi-quantitative connection with the determination of thermodynamical quantities in multifragmentation reactions is done showing that they are affected in a sizeable way only when the flow dominates the global energetic.PACS numbers: 64.10.+h, 25.75.Ld, 25.70.Pq Heavy ion collisions represent a unique opportunity to probe the interdisciplinary field of phase transitions in mesoscopic systems for which a non standard thermodynamics giving rise to negative heat capacities is predicted [1]. An indication of negative heat capacities has been experimentally found [2] in multifragmentation reactions. These results can be considered as a first step towards a quantitative determination of the nuclear phase diagram. Negative heat capacities have also been observed in simulations of self-gravitating systems [3] and in the melting and boiling of clusters [4].An important conceptual problem linked with multifragmentation experiments is that the outcomes of a nuclear collision are not confined in an external container but dynamically deexcite in the vacuum. In the absence of boundary conditions, collective flows can be present at the fragmentation time. Because of this time odd component, one may doubt about the applicability of equilibrium concepts. However, we will show that information theory allows a thermodynamically consistent description of open finite systems in evolution under a collective flow. We will apply this formalism to the Lattice Gas Model [5] for the particular cases of a memory of the entrance channel (transparency) and radial expansion. In both cases the properties of the system appear to be affected in a sizeable way when flow dominates the global energetics.In the Gibbs formulation of statistical mechanics an equilibrium is defined as a collection of different microstates all corresponding to the same macrostate (or statistical ensemble) defined through the average value of (a collection of) collective variables. A practical realization of a Gibbs ensemble is given by the collection of different snapshots of an isolated ergodic system evolving in time, provided that the observation time is much longer than a typical equilibration time . This type of statistical ensemble is not very useful for short-lived open systems as the transient excited states formed in a nuclear collisions. However, ergodicity is not the unique way to produce a Gibbs ensemble . Indeed, within information theory, an equilibrium corresponds to any ensemble of states that maximizes the entropy in a given space under the constraint of (a number of) observables known in average [9]. Therefore, if the nuclear dynamics is sufficiently sensitive to the initial conditions, the ensemble of outcomes...

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“…In order to analyse data in the framework of statistical physics, one must select well defined sources. In central collisions this was done by two techniques: either a selection of compact sources by taking events whose main direction of emission deviates by more than 60 o from the beam direction (Xe+Sn system) [1]; or for the asymmetrical Ni+Au system a discriminant analysis method [2]. In the case of "fused sources" the experimental distributions of excitation energy are narrow.…”

Section: Experimental Event Samplesmentioning

confidence: 99%

Correlations between signals of the liquid-gas phase transition in nuclei

et al. 2005

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Finite systems such as atomic nuclei present at phase transition specific features different from those observed at the thermodynamic limit. Several characteristic signals were found in samples of events resulting from heavy ion collisions at and above the Fermi energy. The concomitant observation of different signatures of a liquid-gas phase transition in nuclei on a given sample strongly supports the occurrence of this transition.

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Multifragmentation of a very heavy nuclear system (I): selection of single-source events

Cited by 52 publications

References 54 publications

Multifragmentation of very heavy nuclear systems (III): Fragment velocity correlations and event topology at freeze-out

Multifragmentation of very heavy nuclear systems (III): Fragment velocity correlations and event topology at freeze-out

Equilibrium under flow

Correlations between signals of the liquid-gas phase transition in nuclei

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