D. Guinet

A hot expanding source in 50 A MeV Xe+Sn central reactions

The INDRA multidetector has been used to study multifragmentation processes in central collisions for the Xe + Sn reaction at 50 A MeV. A single isotropic source formed at an excitation energy of 12 A MeV exhausting most of the emitted charged products has been isolated in such collisions. The fragment kinetic energy spectra indicate a fast disintegration of the system with a radial collective motion of about 2 A MeV. The light charged particle characteristics within this scenario are also discussed.

Charge and current-sensitive preamplifiers for pulse shape discrimination techniques with silicon detectors

New charge- and current-sensitive preamplifiers coupled to silicon detectors and devoted to studies in nuclear structure and dynamics have been developed and tested. For the first time shapes of current pulses from light charged particles and carbon ions are presented. Capabilities for pulse shape discrimination techniques are demonstrated.

Characteristics of the fragments produced in central collisions of129Xe+natSnfrom 32Ato 50AMeV

Characteristics of the primary fragments produced in central collisions of 129Xe + natSn from 32 to 50 AMeV have been obtained. By using the correlation technique for the relative velocity between light charged particles (LCP) and fragments, we were able to extract the multiplicities and average kinetic energy of secondary evaporated LCP. We then reconstructed the size and excitation energy of the primary fragments. For each bombarding energy a constant value of the excitation energy per nucleon over the whole range of fragment charge has been found. This value saturates at 3 AMeV for beam energies 39 AMeV and above. The corresponding secondary evaporated LCP represent less than 40% of all produced particles and decreases down to 23% for 50 AMeV. The experimental characteristics of the primary fragments are compared to the predictions of statistical multifragmentation model (SMM) calculations. Reasonable agreement between the data and the calculation has been found for any given incident energy. However SMM fails to reproduce the trend of the excitation function of the primary fragment excitation energy and the amount of secondary evaporated LCPs.

Particle identification method in the CsI(Tl) scintillator used for the CHIMERA 4π detector

Abstract The charged particle identification obtained by the analysis of signals coming from the CsI(Tl) detectors of the CHIMERA 4 π heavy-ion detector is presented. A simple double-gate integration method, with the use of the cyclotron radiofrequency as reference time, results in low thresholds for isotopic particle identification. The dependence of the identification quality on the gate generation timing is discussed. Isotopic identification of light ions up to Beryllium is clearly seen. For the first time also the identification of Z =5 particles is observed. The identification of neutrons interacting with CsI(Tl) by ( n , α ) and ( n , γ ) reactions is also discussed.

Response of CsI(Tl) scintillators over a large range in energy and atomic number of ions. Part I: recombination and δ-electrons

Abstract 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 δ-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.

Study of intermediate velocity products in the Ar+Ni collisions between 52 and 95 A.MeV

Abstract Intermediate velocity products in Ar+Ni collisions from 52 to 95 A.MeV are studied in an experiment performed at the GANIL facility with the 4 π multidetector INDRA. It is shown that these emissions cannot be explained by statistical decays of the quasi-projectile and the quasi-target in complete equilibrium. Three methods are used to isolate and characterize intermediate velocity products. The total mass of these products increases with the violence of the collision and reaches a large fraction of the system mass in mid-central collisions. This mass is found independent of the incident energy, but strongly dependent on the geometry of the collision. Finally it is shown that the kinematical characteristics of intermediate velocity products are weakly dependent on the experimental impact parameter, but strongly dependent on the incident energy. The observed trends are consistent with a participant–spectator-like scenario or with neck emissions and/or breakup.Intermediate velocity products in Ar+Ni collisions from 52 to 95 A.MeV are studied in an experiment performed at the GANIL facility with the 4

INDEPENDENCE OF FRAGMENT CHARGE DISTRIBUTIONS OF THE SIZE OF HEAVY MULTIFRAGMENTING SOURCES

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Bimodal behavior of the heaviest fragment distribution in projectile fragmentation.

multidetector INDRA. It is shown that these emissions cannot be explained by statistical decays of the quasi-projectile and the quasi-target in complete equilibrium. Three methods are used to isolate and characterize intermediate velocity products. The total mass of these products increases with the violence of the collision and reaches a large fraction of the system mass in mid-central collisions. This mass is found independent of the incident energy, but strongly dependent on the geometry of the collision. Finally it is shown that the kinematical characteristics of intermediate velocity products are weakly dependent on the experimental impact parameter, but strongly dependent on the incident energy. The observed trends are consistent with a participant-spectator like scenario or with neck emissions and/or break-up.

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

Abstract Charged product multiplicities and Z distributions were measured for single multifragmenting sources produced in collisions between 129 Xe + nat Sn and 155 Gd + 238 U at the same available energy per nucleon. Z distributions are found identical for both reactions while fragment multiplicities scale as the charge of the total systems. A complete dynamical simulation, in which multifragmentation originates in the spinodal decomposition of a finite piece of nuclear matter resulting from an incomplete fusion of projectile and target, well accounts for this experimental observation.

Pulse-height defect in the passivated ion-implanted Si detectors of the INDRA array

The charge distribution of the heaviest fragment detected in the decay of quasiprojectiles produced in intermediate energy heavy-ion collisions has been observed to be bimodal. This feature is expected as a generic signal of phase transition in nonextensive systems. In this Letter, we present new analyses of experimental data from Au on Au collisions at 60, 80, and 100 MeV/nucleon showing that bimodality is largely independent of the data selection procedure and of entrance channel effects. An estimate of the latent heat of the transition is extracted.