492 research outputs found

    Nuclear multifragmentation time-scale and fluctuations of largest fragment size

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    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.Comment: Accepted for publication in Physical Review Letters on 8/4/201

    Observation of the lowest energy gamma-ray in any superdeformed nucleus : 196Bi

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    New results on the superdeformed 196^{196}Bi nucleus a re reported. We have observed with the EUROBALL IV γ\gamma-ray spectrometer array a superdeformed trans ition of 124 keV which is the lowest observed energy γ\gamma-ray in any superdeformed nucleus. We have de velopped microscopic cranked Hartree-Fock-Bogoliubov calculations using the SLy4 effective force and a realistic surface p airing which strongly support the Kπ=2K^\pi=2^-(π\pi[651]1/2ν\otimes \nu[752]5/2) assignment of this su perdeformed band

    Constrained caloric curves and phase transition for hot nuclei

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    Simulations based on experimental data obtained from multifragmenting quasi-fused nuclei produced in central 129^{129}Xe + nat^{nat}Sn collisions have been used to deduce event by event freeze-out properties in the thermal excitation energy range 4-12 AMeV [Nucl. Phys. A809 (2008) 111]. From these properties and the temperatures deduced from proton transverse momentum fluctuations, constrained caloric curves have been built. At constant average volumes caloric curves exhibit a monotonic behaviour whereas for constrained pressures a backbending is observed. Such results support the existence of a first order phase transition for hot nuclei.Comment: 14 pages, 5 figures, accepted in Physics Letters

    Isospin diffusion in semi-peripheral 58Ni^{58}Ni + 197Au^{197}Au collisions at intermediate energies (I): Experimental results

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    Isospin diffusion in semi-peripheral collisions is probed as a function of the dissipated energy by studying two systems 58Ni^{58}Ni + 58Ni^{58}Ni and 58Ni^{58}Ni + 197Au^{197}Au, over the incident energy range 52-74\AM. A close examination of the multiplicities of light products in the forward part of phase space clearly shows an influence of the isospin of the target on the neutron richness of these products. A progressive isospin diffusion is observed when collisions become more central, in connection with the interaction time

    Production of α\alpha-particle condensate states in heavy-ion collisions

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    The fragmentation of quasi-projectiles from the nuclear reaction 40Ca^{40}Ca + 12C^{12}C at 25 MeV/nucleon was used to produce excited states candidates to α\alpha-particle condensation. The experiment was performed at LNS-Catania using the CHIMERA multidetector. Accepting the emission simultaneity and equality among the α\alpha-particle kinetic energies as experimental criteria for deciding in favor of the condensate nature of an excited state, we analyze the 02+0_2^+ and 22+2_2^+ states of 12^{12}C and the 06+0_6^+ state of 16^{16}O. A sub-class of events corresponding to the direct 3-α\alpha decay of the Hoyle state is isolated.Comment: contribution to the 2nd Workshop on "State of the Art in Nuclear Cluster Physics" (SOTANCP2), Universite Libre de Bruxelles (Belgium), May 25-28, 2010, to be published in the International Journal of Modern Physics

    Isospin Diffusion in 58^{58}Ni-Induced Reactions at Intermediate Energies

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    Isospin diffusion is probed as a function of the dissipated energy by studying two systems 58^{58}Ni+58^{58}Ni and 58^{58}Ni+197^{197}Au, over the incident energy range 52-74\AM. 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 \AM{} is estimated to 130±\pm10 fm/cc

    Coulomb chronometry to probe the decay mechanism of hot nuclei

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    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±\pm0.5 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.Comment: 12 pages; 13 Figures; 4 Table; Accepted for publication in Physical Review
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