J.D. Frankland

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.

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.

Universal fluctuations in heavy-ion collisions in the Fermi energy domain

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.

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

Abstract The light output of the 324 CsI(Tl) scintillators of INDRA has been measured over large ranges in energy: 1– 80 AMeV and in atomic number of incident ions: Z =1–60. An analytical expression for the non-linear total light response as a function of the energy and the identity of the ion is developed. It depends on four parameters. For three of them, connected to CsI(Tl) intrinsic characteristics, fixed values are proposed. Two applications are presented: energy calibration and fragment identification in telescopes using a CsI(Tl) crystal as residual energy detector.

Isotopic dependence of the nuclear caloric curve

We discuss the scaling laws of both the charged fragments multiplicity n fluctuations and the charge of the largest fragment Z(max) fluctuations for Xe + Sn collisions in the range of bombarding energies between 25A MeV and 50A MeV. We show at E(lab) > or similar to 32 MeV/A the transition in the fluctuation regime of Z(max) which is compatible with the transition from the ordered to disordered phase of excited nuclear matter. The size (charge) of the largest fragment is closely related to the order parameter characterizing this process.

Model-independent tracking of criticality signals in nuclear multifragmentation data

Abstract The pulse-height defect (PHD) of 36Ar, 58Ni, 129Xe, 181Ta and 197Au ions in the 180 passivated ion-implanted silicon detectors of the INDRA array has been measured. The detectors faced the target with the low electric field side. The charge encoding ensured a low ballistic deficit. Detectors with the same nominal characteristics and electric field strength show a PHD dependence on the individual silicon wafer. They are classified and calibrated by using an empirical parametrization which relates the PHD to the total energy through a Z-depending power law. A PHD analytical formula, based on a simple recombination model, is also proposed. It considers a realistic charge density variation with the position coordinate on the ion path. This new formula is successfully confronted to some experimental data.