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Suppression of multiplicity fluctuations has been observed for three light fermions (protons, tritons and 3He) in the multifragmentation of reconstructed hot quasi-projectiles produced in collisions of 32S (45 MeV/nucleon) with 112Sn. This suppression, predicted by recent calculations, is attributed to Pauli blocking and has also been observed in experiments with trapped Fermi gases. Experimental results on nuclear temperature and density employing a quantal approach based on momentum and multiplicity fluctuations are also presented. The extracted temperatures show a noticeable reduction when compared to a similarly derived classical method. This reduction in temperature is in agreement with previous predictions indicating that classically derived methods overpredict nuclear temperature as they do not take into account the Fermi motion of the nucleons. The present results underline the role of quantum statistics in nuclear disassembly and suggest the need for proper quantum treatment when dealing with the thermodynamic properties of fragmenting heavy ions. © 2014 IOP Publishing Ltd.

The production of fragments from a broad range of reconstructed quasi-projectiles obtained in the interaction of 32S (45 MeV/nucleon) with 112Sn was studied. A good description of the experimental data on the multifragmentation of these light quasi-projectiles with a model framework based on deep inelastic transfer followed by SMM (statistical multifragmentation model) was obtained. The charge and mass distributions of the observed fragments show that the break-up of a given quasi-projectile source is highly correlated to its isospin composition. The sensitivity of the hot primary fragments to the symmetry energy was investigated in detail. It was found that for the present light systems (A30), a good description of the experimental data on the charge distributions, the N/Z distributions and the isotopic distributions of the fragments is obtained by the SMM calculations involving the standard (Csym = 25 MeV), as well as, a reduced value of the symmetry energy (Csym = 8 MeV). However, the reduced value of the symmetry energy appears to provide a better description of the isotopic distributions in most of the cases. This is in agreement with an overall reduction of the symmetry energy of primary fragments indicated by a number of multifragmentation studies of heavier systems. © 2012 IOP Publishing Ltd.

Correlations of midrapidity light charged particles (LCPs) and intermediate mass fragments (IMFs) with projectile-like fragments (PLFs) have been examined from the 35 MeV/u 70Zn+70Zn, 64Zn+64Zn, and 64Ni+64Ni reaction systems. A new method was developed to examine the flow of the particles with respect to the PLF. The invariant PLF-scaled flow allowed for the dynamics of the midrapidity Z=1-4 particles to be studied. Strong differences in the PLF-scaled flow were observed between the different isotopes. In particular, the most n-rich LCPs exhibited a negative PLF-scaled flow in comparison to the other LCPs. A classical molecular dynamics model and a three-body Coulomb trajectory simulation were both used to show that the PLF-scaled flow observable could be connected to the average order of emission of the LCPs. The experimental results suggest that the midrapidity region is preferentially populated with neutron-rich LCPs and Z=3-4 IMFs at a relatively early stage in the collision. The deuteron and 3He particles are emitted later followed, lastly, by protons and alphas. The average order of emission of the midrapidity LCPs was extracted from the constrained molecular dynamics simulations and showed good agreement with the emission order suggested by the experimental PLF-scaled flow results. © 2012 American Physical Society.

Methods of extraction of the symmetry energy (or enthalpy) coefficient to temperature ratio from isobaric and isotopic yields of fragments produced in Fermi-energy heavy-ion collisions are discussed. We show that the methods are consistent when the hot fragmenting source is well characterized and its excitation energy and isotopic composition are properly taken into account. The results are independent of the mass number of the detected fragments, which suggests that their fate is decided very early in the reaction. © 2012 American Physical Society

Peripheral collisions of Ca40 and Ca48 projectiles at 32 MeV/nucleon on Sn112 and Sn124 targets were studied in this work. The fragments of the projectile-like source (quasiprojectile) were collected with a charged-particle multidetector array. The average value of the neutron-to-proton ratio N/Z of the quasiprojectiles formed in the reactions was determined with two approaches. The first is a direct reconstruction approach using isotopically resolved fragments and is hindered by undetected neutrons leading to lower N/Z values. The second approach, based on the assumption of early fragment formation, employs yield ratios of fragment isobars and is not hindered by undetected neutrons. Using this approach, the amount of N/Z mixing that occurred in the quasiprojectiles (compared to a fully N/Z equilibrated system) was found to be approximately 53%. The experimental results were compared with model calculations. First, the phenomenological DIT (deep inelastic transfer) model was used, followed by the statistical multifragmentation model (SMM). The results of these calculations are in close agreement with the data and indicate that the mean number of undetected neutrons increases with the N/Z of the composite system, accounting for the difference observed between the two approaches of quasiprojectile N/Z determination. Second, the microscopic transport model IBUU (isospin-dependent Boltzmann-Uehling-Uhlenbeck) was employed, providing preliminary results in reasonable agreement with the data. The determination of the degree of N/Z equilibration employing the present fragment yield ratio approach may provide a valuable probe to study the isospin part of the nuclear equation of state in conjunction with detailed microscopic models of the collisions in the Fermi energy regime. © 2010 The American Physical Society.