P. Marini

Persistence of odd-even staggering in charged fragment yields from the

Odd-even staggering effects on charge distributions are investigated for fragments produced in semiperipheral and central collisions of 112Sn+58Ni at 35 MeV/nucleon. For fragments with Z<16 one observes a clear overproduction of even charges, which decreases for heavier fragments. In peripheral collisions staggering effects persist up to Z about 40. For light fragments, staggering appears to be substantially independent of the centrality of the collisions, suggesting that it is mainly related to the last few steps in the decay of hot nuclei.

^{112}Sn + ^{58}Ni

Distributions of the largest fragment charge, Zmax, in multifragmentation reactions around the Fermi energy can be decomposed into a sum of a Gaussian and a Gumbel distribution, whereas at much higher or lower energies one or the other distribution is asymptotically dominant. We demonstrate the same generic behavior for the largest cluster size in critical aggregation models for small systems, in or out of equilibrium, around the critical point. By analogy with the time-dependent irreversible aggregation model, we infer that Zmax distributions are characteristic of the multifragmentation time scale, which is largely determined by the onset of radial expansion in this energy range.

collision at 35 MeV/nucleon

In 129 Xe+ nat Sn central collisions from 8 to 25 MeV/A, the three-fragment exit channel occurs with a significant cross section. We show that these fragments arise from two successive binary splittings of a heavy composite system. The sequence of fragment production is determined. Strong Coulomb proximity effects are observed in the three-fragment final state. A comparison with Coulomb trajec-tory calculations shows that the time scale between the consecutive break-ups decreases with increasing bombarding energy, becoming quasi-simultaneous above excitation energy E * = 4.0±0.5 MeV/A. This transition from sequential to simultaneous break-up was interpreted as the signature of the onset of multifragmentation for the three-fragment exit channel in this system.

Nuclear multifragmentation time-scale and fluctuations of largest fragment size

Abstract We report on first experimental observations of nuclear fermionic and bosonic components displaying different behaviours in the decay of hot Ca projectile-like sources produced in mid-peripheral collisions at sub-Fermi energies. The experimental setup, constituted by the coupling of the INDRA 4 π detector array to the forward angle VAMOS magnetic spectrometer, allowed to reconstruct the mass, charge and excitation energy of the decaying hot projectile-like sources. By means of quantum-fluctuation analysis techniques, temperatures and local partial densities of bosons and fermions could be correlated to the excitation energy of the reconstructed system. The results are consistent with the production of dilute mixed systems of bosons and fermions, where bosons experience higher phase-space and energy density as compared to the surrounding fermionic gas. Our findings recall phenomena observed in the study of Bose condensates and Fermi gases in atomic traps despite the different scales.

Coulomb chronometry to probe the decay mechanism of hot nuclei

Abstract. Symmetry energy is a key quantity in the study of the equation of state of asymmetric nuclear matter. Heavy ion collisions at low and intermediate energies, performed at Laboratori Nazionali di Legnaro and Laboratori Nazionali del Sud, can be used to extract information on the symmetry energy coefficient Csym, which is currently poorly known but relevant both for astrophysics and for deeper knowledge of the structure of exotic nuclei.

Signals of Bose Einstein condensation and Fermi quenching in the decay of hot nuclear systems

Abstract.In the Fermi energy domain, the temperature of hot nuclei can be determined using the energy spectra of evaporated light charged particles. But this method of measurement is not without difficulties both theoretical and experimental. The present study aims to disentangle the respective influences of different factors on the quality of this measurement: the physics, the detection (a

Isotope analysis in central heavy ion collisions at intermediate energies

4\pi

Understanding the thermometry of hot nuclei from the energy spectra of light charged particles

4π detector array such as INDRA) and the experimental procedure. This analysis demonstrates the possibility of determining from an energy spectrum, with an accuracy of about 10%, the true apparent temperature felt by a given type of particle emitted from a hot nucleus. This temperature allows to deduce the initial temperature using an appropriate method. However, three conditions are necessary: a perfect particle detector, important statistics and very weak secondary emissions. According to the GEMINI event generator, for hot intermediate mass nuclei, only deuterons and tritons could meet these conditions. In this case the determination may be better than 15%. With a realistic experimental device, insufficient angular resolution and topological distortions, caused by detection, can distort spectra to the point where it is very difficult to determine the apparent temperature correctly. Experimental reconstruction of the moving frame of the hot nucleus can also be responsible for this deterioration.

Light charged clusters emitted in 32 MeV/nucleon

Nuclear particle production from peripheral to central events is presented. N/Z gradient between projectile and target is studied using the fact that two reactions have the same projectile+target N/Z and so the same neutron to proton ratio for the combined system. Inclusive data study in the forward part of the center of mass indicates that N/Z equilibration between the projectile-like and the target-like is achieved for central collisions. Particles are also produced from mid-rapidity region. 3He mean pre-equilibrium character is evidenced and 6He production at mid-rapidity implies a neutron enrichment phenomenon of the projectile target interacting zone.