Search

The Intermediate Mass Fragments emission probability from Projectile-Like Fragment break-up in semi-peripheral reactions has been measured in collisions of $^{124}$Xe projectiles with two different targets of $^{64}$Ni and $^{64}$Zn at the laboratory energy of 35 \amev. The two colliding systems differ only for the target atomic number Z and, consequently, for the Isospin $N/Z$ ratio. An enhancement of Intermediate Mass Fragments production for the neutron rich $^{64}$Ni target, with respect to the $^{64}$Zn, is found. In the case of one Intermediate Mass Fragment emission, the contributions of the dynamical and statistical emissions have been evaluated, showing that the increase of the effect above is due to an enhancement of the dynamical emission probability, especially for heavy IMFs (Z$\gtrsim$ 7). This proves an influence of the target Isospin on inducing the dynamical fragment production from Projectile-Like Fragment break-up. In addition, a comparison of the Xe+Ni,Zn results with the previously studied $^{112,124}Sn+^{58,64}Ni$ systems is discussed in order to investigate the influence of the projectile Isospin alone and to disentangle between Isospin effects against system-size effects on the emission probability. These comparisons suggest that the prompt-dynamical emission is mainly ruled by the $N/Z$ content of, both, projectile and target; for the cases here investigated, the influence of the system size on the dynamical emission probability can be excluded.

Data from the experiment on the 197Au + 197Au reaction at 23 AMeV are analyzed with an aim to find signatures of exotic nuclear configurations such as toroid-shaped objects. The experimental data are compared with predictions of the ETNA code dedicated to look for such configurations and with the QMD model. A novel criterion of selecting events possibly resulting from the formation of exotic freeze-out configurations, "the efficiency factor", is tested. Comparison between experimental data and model predictions may indicate for the formation of flat/toroidal nuclear systems.

A project of using a target consisting of the mixture of (249-252)Cf isotopes to be bombarded with the 48Ca beam, aimed to synthesize new isotopes of the heaviest known element Z = 118, is under way at the FLNR in Dubna. In the present work excitation functions for all the reactions: 249Cf(48Ca,xn)(297-x)118, 250Cf(48Ca,xn)(298-x)118, 251Cf(48Ca,xn)(299-x)118 and 252Cf(48Ca,xn)(300-x)118 have been calculated in the framework of the fusion-by-diffusion model, assuming fission barriers, ground-state masses and shell effects of the superheavy nuclei predicted by Kowal et al. Energy dependence of the effective cross sections for the synthesis of selected new isotopes: (293)118, (294)118, (295)118 and (296)118 is predicted for the particular isotopic composition of the Cf target prepared for the Dubna experiment., Comment: 5 pages, 2 figures

We show new data from the $^{64}$Ni+$^{124}$Sn and $^{58}$Ni+$^{112}$Sn reactions studied in direct kinematics with the CHIMERA detector at INFN-LNS and compared with the reverse kinematics reactions at the same incident beam energy (35 A MeV). Analyzing the data with the method of relative velocity correlations, fragments coming from statistical decay of an excited projectile-like (PLF) or target-like (TLF) fragments are discriminated from the ones coming from dynamical emission in the early stages of the reaction. By comparing data of the reverse kinematics experiment with a stochastic mean field (SMF) + GEMINI calculations our results show that observables from neck fragmentation mechanism add valuable constraints on the density dependence of symmetry energy. An indication is found for a moderately stiff symmetry energy potential term of EOS., Comment: Talk given by E. De Filippo at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS)

We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $<$N/Z$>$ isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio $<$N/Z$>$ distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy., Comment: 17 pages, 7 figures; submitted to Physical Rev. C

A complete set of existing data on hot fusion reactions leading to synthesis of superheavy nuclei of Z =114-118, obtained in a series of experiments in Dubna and later in GSI Darmstadt and LBNL Berkeley, was analyzed in terms of a new angular-momentum dependent version of the Fusion by Diffusion (FBD) model with fission barriers and ground-state masses taken from the Warsaw macroscopic-microscopic model (involving non-axial shapes) of Kowal et al. The only empirically adjustable parameter of the model, the injection-point distance (sinj), has been determined individually for all the reactions and very regular systematics of this parameter have been established. The regularity of the obtained sinj systematics indirectly points at the internal consistency of the whole set of fission barriers used in the calculations. Having fitted all the experimental excitation functions for elements Z = 114-118, the FBD model (with the new sinj systematics) was used to predict cross sections for synthesis of elements Z = 119 and 120. Regarding prospects to produce the new element Z = 119, our calculations prefer the 252Es(48Ca,xn)300-x119 reaction, for which the synthesis cross section of about 0.2 pb in 4n channel at Ec.m.= 220 MeV is expected. The most favorable reaction to synthesize the element Z = 120 turns out to be 249Cf(50Ti,xn)299-x120, but the predicted cross section for this reaction is only 6 fb (for 3n and 4n channels).