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N. Le Neindre

Publications and source records attributed to N. Le Neindre.

72 records · Page 4Linked to original sources
arXiv2005

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.

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arXiv2005

Estimate of average freeze-out volume in multifragmentation events

An estimate of the average freeze-out volume for multifragmentation events is presented. Values of volumes are obtained by means of a simulation using the experimental charged product partitions measured by the 4pi multidetector INDRA for 129Xe central collisions on Sn at 32 AMeV incident energy. The input parameters of the simulation are tuned by means of the comparison between the experimental and simulated velocity (or energy) spectra of particles and fragments.

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arXiv2005

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.

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arXiv2004

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

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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arXiv2003

Liquid-gas phase transition in hot nuclei studied with INDRA

Thanks to the high detection quality of the INDRA array, signatures related to the dynamics (spinodal decomposition) and thermodynamics (negative microcanonical heat capacity) of a liquid-gas phase transition have been simultaneously studied in multifragmentation events in the Fermi energy domain. The correlation between both types of signals strongly supports the existence of a first order phase transition for hot nuclei.

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arXiv2003

Dynamical effects in multifragmentation at intermediate energies

The fragmentation of the quasi-projectile is studied with the INDRA multidetector for different colliding systems and incident energies in the Fermi energy range. Different experimental observations show that a large part of the fragmentation is not compatible with the statistical fragmentation of a fully equilibrated nucleus. The study of internal correlations is a powerful tool, especially to evidence entrance channel effects. These effects have to be included in the theoretical descriptions of nuclear multifragmentation.

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arXiv2002

Dynamics and thermodynamics of phase transition in hot nuclei

The dynamics and thermodynamics of phase transition in hot nuclei are studied through experimental results on multifragmentation of heavy systems (A>200) formed in central heavy ion collisions. Different signals indicative of a phase transition studied in the INDRA collaboration are presented and their consistency is stressed.

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arXiv2002

Critical behaviors in central and peripheral collisions: a comparative analysis

Quasi-projectile events from peripheral 35 A.MeV Au+ Au collisions are compared to central Au + C, Au + Cu and Au + Au events in the same range of excitation energy in terms of critical partitions and critical exponents. All the different data sets coherently point to a value E*c=4.5 A.MeV for the apparent critical excitation energy. The critical exponents tau, sigma are compatible with the observation of a liquid-gas phase transition for these systems.

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arXiv2001

Mass and charge identification of fragments detected with the Chimera Silicon-CsI(Tl) telescopes

Mass and charge identification of charged products detected with Silicon-CsI(Tl) telescopes of the Chimera apparatus is presented. An identification function, based on the Bethe-Bloch formula, is used to fit empirical correlation between Delta E and E ADC readings, in order to determine, event by event, the atomic and mass numbers of the detected charged reaction products prior to energy calibration.

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arXiv2001

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.

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arXiv2001

Response of CsI(Tl) scintillators over a large range in energy and atomic number of ions (Part II): calibration and identification in the INDRA array

The light output of the 324 CsI(Tl) scintillators of INDRA has been measured over a large range both in energy: 1 - 80 AMeV and in atomic number of incident ions: Z = 1 - 60. An analytical expression for the nonlinear total light response as a function of the energy and the identity of the ion is proposed. It depends on four parameters. For three of them, connected to CsI(Tl) intrinsic characteristics, recommended fixed values are proposed. They are issued from the comparative study of the forward scintillators of INDRA, based on intermediate mass fragment data. The fourth one, related to light collection and to the gain of the associated photomultiplier, is particular and may be accurately obtained afterwards, from light charged particle data. Two applications are presented: fragment identification in telescopes using a CsI(Tl) crystal as residual energy detector and the scintillator energy calibration. The results are successfully confronted to heavy fragment experimental data.

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arXiv2001

On the reliability of negative heat capacity measurements

A global protocol for the thermostatistical analysis of hot nuclear sources is discussed. Within our method of minimization of variances we show that the abnormal kinetic energy fluctuation signal recently reported in different experimental data (M.D'Agostino et al.-Phys. Lett. B 473 (2000) 219, N. Le Neindre et al.- contr. to the XXXVIII Bormio Winter Meeting on Nucl. Phys. (2001) 404) is a genuine signal of a first order phase transition in a finite system.

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arXiv2000

Effect of the intermediate velocity emissions on the quasi-projectile properties for the Ar+Ni system at 95 A.MeV

The quasi-projectile (QP) properties are investigated in the Ar+Ni collisions at 95 A.MeV taking into account the intermediate velocity emission. Indeed, in this reaction, between 52 and 95 A.MeV bombarding energies, the number of particles emitted in the intermediate velocity region is related to the overlap volume between projectile and target. Mean transverse energies of these particles are found particularly high. In this context, the mass of the QP decreases linearly with the impact parameter from peripheral to central collisions whereas its excitation energy increases up to 8 A.MeV. These results are compared to previous analyses assuming a pure binary scenario.

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arXiv1999

Negative heat capacity in the critical region of nuclear fragmentation: an experimental evidence of the liquid-gas phase transition

An experimental indication of negative heat capacity in excited nuclear systems is inferred from the event by event study of energy fluctuations in $Au$ quasi-projectile sources formed in $Au+Au$ collisions at 35 A.MeV. The excited source configuration is reconstructed through a calorimetric analysis of its de-excitation products. Fragment partitions show signs of a critical behavior at about 5 A.MeV excitation energy. In the same energy range the heat capacity shows a negative branch providing a direct evidence of a first order liquid gas phase transition.

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arXiv1999

Thermodynamical features of multifragmentation in peripheral Au + Au Collisions at 35 A.MeV

The distribution of fragments produced in events involving the multifragmentation of excited sources is studied for peripheral Au + Au reactions at 35 A.MeV. The Quasi-Projectile has been reconstructed from its de-excitation products. An isotropic emission in its rest frame has been observed, indicating that an equilibrated system has been formed. The excitation energy of the Quasi-Projectile has been determined via calorimetry. A new event by event effective thermometer is proposed based on the energy balance. A peak in the energy fluctuations is observed related to the heat capacity, suggesting that the system undergoes a liquid-gas type phase transition at an excitation energy about 5 A.MeV and a temperature 4 - 6 MeV, dependent on the freeze-out hypothesis. By analyzing different regions of the Campi-plot, the events associated with the liquid and gas phases as well as the critical region are thermodynamically characterized. The critical exponents, tau, beta,gamma, extracted from the high moments of the charge distribution are consistent with a liquid-gas type phase transition.

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