Search

Isospin diffusion is probed as a function of the dissipated energy by studying two systems 58Ni+58Ni and 58Ni+197Au, over the incident energy range 52-74A MeV. Experimental data are compared with the results of a microscopic transport model with two different parameterizations of the symmetry energy term. A better overall agreement between data and simulations is obtained when using a symmetry term with a potential part linearly increasing with nuclear density. The isospin equilibration time at 52 A MeV is estimated to 130 ± 10 fm/c. [ABSTRACT FROM AUTHOR]

A new detector system dedicated for very/super heavy elements (VHE/SHE) detection that decay by spontaneous fission is presented. Such a decay mode of nuclei can be found e.g. in the region of Z≈100 (Fermium). Future experiments realized in the frame of French-Polish collaboration at the cyclotrons in GANIL and in the Heavy Ion Laboratory (HIL), University of Warsaw, is described. The results of test measurements made in the HIL for reactions 20Ne(8 A.MeV)+120Sn, 179Au are presented. [ABSTRACT FROM AUTHOR]

For fragments emitted in the reactions 124Sn + 64Ni and 112Sn + 58Ni at 35 AMeV, isotopic composition and velocity correlations have been studied as a function of the centrality of the collision, using the 4π Chimera multidetector. We have investigated the time scale for fragments formation, in order to distinguish between prompt dynamical and sequential statistical emission. Promptly emitted light fragments (Z ≤9) produced in the mid-rapidity domain are characterised by larger N/Z ratio and stronger angular anisotropies than those produced in sequential statistical emission. Results are compared with stochastic BNV code simulations obtained for primary fragments. Valuable information on the symmetry term of the nuclear equation of state at sub-saturation densities are obtained. [ABSTRACT FROM AUTHOR]

In the paper we present scintillation-ionization detector (SID) -- a new device for support of the superheavy elements (SHE) identification in the standard, complete fusion methods. We highlight problems with background effects in SHE production and their minimization by introducing SID to the detection set-up at GANIL. We also point possible application of this detector in alternative approach for superheavy elements production. [ABSTRACT FROM AUTHOR]

Investigations on the influence of the neutron enrichment on the decay channels of excited nuclei are presented. Characteristics of fragments with charge 6 ≤ Z ≤ 28 emitted in 78,82Kr+40Ca at 5.5 MeV/A reactions were measured at the GANIL facility. Data are compatible with an emission process from compound nucleus and are discussed in the framework of the transition state model. [ABSTRACT FROM AUTHOR]

Cross sections, kinetic energy and angular distributions of fragments with charge 6 ≤ Z ≤ 28 emitted in 78,82Kr+40C at 5.5 MeV/A reactions were measured at the GANIL facility using the INDRA apparatus. This experiment aims to investigate the influence of the neutron enrichment on the decay mechanism of excited nuclei. Data are discussed in comparison with predictions of transition state and Hauser-Feshbach models. [ABSTRACT FROM AUTHOR]

The blocking technique in single crystals has been applied to reaction time measurements for the 238U + Ge system at 6.1 MeV/nucleon. Backed up with a reaction mechanism analysis using the INDRA 4π detector, it provides a direct experimental evidence for Z = 124 compound nuclei living longer than 10-18 s, indicating thus very high fission barriers for this element. [ABSTRACT FROM AUTHOR]

The odd- Z isotope 255Lr, its daughter 251Md and grand-daughter 247Es were studied in two experiments performed at GANIL and the University of Jyväskylä. The 255Lr nuclei were produced using the cold fusion-evaporation reaction 209Bi(48Ca, 2n)255Lr at a bombarding energy of 217MeV. The single-particle structure and decay properties were investigated using α, γ and electron spectroscopy. The ground-state spin and parity could be assigned for 255Lr (1/2-) and 251Md (7/2-). States corresponding to the 7/2+[633], 7/2-[514] and 1/2-[521] Nilsson orbitals were observed. Results are compared to experimental data obtained in neighbouring isotopes and to Hartree-Fock-Bogoliubov calculations using the Skyrme interaction SLy4 and a density-dependent pairing interaction. The position of the 1/2-[521] orbital from the spherical 2 f 5/2 shell is discussed. [ABSTRACT FROM AUTHOR]

Using the 4π CHIMERA detector system we have observed a dynamical, non-equilibrated fission of projectile-like fragments as well as an equilibrated fission component in collisions 124Sn + 64Ni and 112Sn + 58Ni at 35A MeV. The velocity and angular distributions of projectile-like fission fragments were analyzed. The contribution of the "dynamical fission" component is larger in the neutron rich 124Sn + 64Ni system than in the neutron poor 112Sn + 58Ni one. [ABSTRACT FROM AUTHOR]

Ar + Ni and Ni + Ni collisions are investigated between 32 and around 100A MeV incident energy with the 4π multidetector INDRA. Fusion cross-sections are found to decrease from ∼ 180mb at 32A MeV to zero above 50A MeV. Other experimental results, for light systems, are compared. Moreover, theoretical works are discussed and fusion cross-sections, calculated from two dynamical simulations based on nuclear Boltzmann equation (Boltzmann-Nordheim-Vlasov and Landau-Vlasov models), are also compared to experimental results. [ABSTRACT FROM AUTHOR]

Directed and elliptic flow for the 197Au+197Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ NN and demonstrate the importance of angular momentum conservation in transport codes at low energies. [ABSTRACT FROM AUTHOR]

Low-energy π+ (Eπ ≲ 35 MeV) from 12C + 197Au collisions at incident energies from 300 to 1800 MeV per nucleon were detected with the Si-Si(Li)-Csl(TI) calibration telescopes of the INDRA multidetector. The inclusive angular distributions are approximately isotropic, consistent with multiple rescattering in the target spectator. The multiplicity correlations of the low-energy pions and of energetic protons (Ep ≳ 150 MeV) with intermediate-mass fragments were determined from the measured coincidence data. The deduced correlation functions 1 + R ≈ 1.3 for inclusive event samples reflect the strong correlations evident from the common impact parameter dependence of the considered multiplicities. For narrow impact parameter bins (based on charged-particle multiplicity), the correlation functions are close to unity and do not indicate strong additional correlations. Only for pions at high particle multiplicities (central collisions) a weak anticorrelation is observed, probably due to a limited competition between these emissions. Overall, the results are consistent with the equilibrium assumption made in statistical multifragmentation scenarios. Predictions obtained with intranuclear-cascade models coupled to the Statistical Multifragmentation Model are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The transport properties of the 36Ar + 58Ni system at 95 A. MeV measured with the INDRA array, are studied within the BNV kinetic equation. A general protocol of comparison between the N-body experimental fragment information and the one-body distribution function is developed using global variables, with a special focus on charge density. This procedure avoids any definition of sources and any use of an afterburner in the simulation. We shall discuss the feasibility of such an approach and the distortions induced by the finite detection efficiency and the completeness requirements of the data selection. The sensitivity of the different global observables to the macroscopic parameters of the effective nuclear interaction will be studied in detail. [ABSTRACT FROM AUTHOR]

The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function of impact parameter. The results are compared with experimental data from the 36Ar + 58Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity. [ABSTRACT FROM AUTHOR]

Proton and deuteron correlation functions have been investigated with both impact parameter and emission source selections. The correlations of the system 129Xe+NatSn at 50 AMeV have been measured with the 4π INDRA which provides a complete kinematical description of each event. The emission time scale analyzed with a quantum model reveals the time sequence of the light particles emitted by the projectile-like fragment. The short and constant emission time of the proton, independent of the impact parameter, can be attributed to a preequilibrium process. [ABSTRACT FROM AUTHOR]

Vaporized sources produced in collisions between 36Ar and 58Ni at 95 MeV per nucleon have been detected with the multidetector INDRA. Complete information concerning the deexcitation properties of quasi-projectiles, including second moments of chemical composition, is compared to a quantum statistical model describing a gas of fermions and bosons in thermal and chemical equilibrium. Inclusions in the calculation of all known discrete levels of nuclear species which deexcite into light particles and of a final state excluded volume interaction are found decisive to very well reproduce the experimental data, which strongly supports that thermodynamical equilibrium was achieved at freeze-out for such sources. [ABSTRACT FROM AUTHOR]

Fusion-fission and fully energy-damped binary processes of the 35Cl+24Mg reaction were investigated using particle-particle coincidence techniques at a 35Cl bombarding energy of Elab≈ 8 MeV/nucleon. Inclusive data were also taken in order to determine the partial wave distribution of the fusion process. The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with a relatively large multiplicity of secondary light-charged particles emitted by the two primary excited fragments in the exit channel. No evidence is observed for ternary-breakup processes, as expected from the systematics recently established for incident energies below 15 MeV/nucleon and for a large number of reactions. The binary-process results are compared with predictions of statistical-model calculations. The calculations were performed using the Hauser-Feshbach method, based on the available phase space at the scission point of the compound nucleus. This new method uses temperature-dependent level densities and its predictions are in good agreement with the presented experimental data, thus consistent with the fusion-fission origin of the binary fully-damped yields. [ABSTRACT FROM AUTHOR]

In order to verify the effect of the ablation stage on the fast abrasion mechanism, detailed evaporative calculations have been performed on the primary projectile and target-like fragments issued from the reactionsAr+Al andCa+Al. The results account for many of the experimental features observed in the projectile and target-like fragments produced at intermediate energies. However it is pointed out that, in order to get a better agreement between theory and experimental data, the primary projectile and target-like fragments should carry a more substantial excitation energy than predicted by a purely geometric abrasion model. [ABSTRACT FROM AUTHOR]

The properties of the two-body channels populated in theCl +C reaction, at a bombarding energy of 180 KeV, have been studied by means of a kinematical coincidence technique. Binary reaction products show full energy equilibration and isotropic angular distributions in the center-of-mass frame. The asymmetrical elemental distribution of the fully-damped yields, similar to that observed previously in theS +Mg reaction, suggests the occurence of fusion-fission rather than orbiting. [ABSTRACT FROM AUTHOR]

The properties of the two-body channels in theCl+Mg reaction at a bombarding energy of 275 MeV, have been investigated by using fragment-fragment coincident techniques. The exclusive data show that the majority of events arises from a binary-decay process. The rather large number of secondary light charged-particles emitted from the two excited exit fragments are consistent with the expectations of the Extended Hauser-Feshbach Method. Therefore no evidence for the occurence of ternary break-up events is observed. [ABSTRACT FROM AUTHOR]