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Binary collisions of either stable or radioactive heavy ions at Fermi energies allow to study the nuclear reaction mechanisms under dynamical conditions of non-equilibrium and the formation of transient pieces of nuclear matter of very short mean life times at sub-normal density. An important role in the evolutionary phase of the collision is played by the gradient of the nuclear density affecting the isospin asymmetry of the reaction products by typical transport phenomena such as the isospin diffusion and drift. Experimental determination of the value of the nuclear matter density in the early phase of the collision is a crucial step towards understanding the underlying mechanism responsible for the production of clusters. In this paper a method for evaluating the nuclear density in semi-peripheral collisions in the reaction $$^{124}Sn + ^{64}Ni$$ at 35 MeV/nucleon as studied with the CHIMERA multi-particle detector is described.

Excitation functions for fusion-$xn$ evaporation reaction channels induced by $^{48}\mathrm{Ca}$ as well as by heavier projectiles (usually leading to smaller cross sections) on actinide targets were calculated in the framework of the fusion-by-diffusion (FBD) model. For the first time, in this approach, channels in which a proton ($pxn$) or alpha particle ($\ensuremath{\alpha}xn$) is evaporated have been included in the first step of the de-excitation cascade. To calculate the synthesis cross sections entry data such as fission barriers, ground-state masses, deformations, and shell effects of the superheavy nuclei calculated in a consistent way within the Warsaw macroscopic-microscopic model were used. The only adjustable parameter of the FBD model is the injection point distance ${s}_{inj}$. The systematics determined in our previous analysis of experimental cross sections for the synthesis of superheavy nuclei of $Z=114--118$ has been used. Excitation functions for the synthesis of selected (cross section above a few fb) new superheavy nuclides in the range of atomic numbers 112--120 are presented. Observation of 21 new heaviest isotopes is also predicted. A realistic discussion of the FBD model uncertainties is presented for the first time.

The FOPI Collaboration at the GSI SIS-18 synchrotron measured charged kaons from central and semicentral collisions of Ni+Ni at a beam energy of 1.91A GeV. We present the distribution of the K−/K+ ratio on the energy vs polar angle plane in the nucleon-nucleon center-of-mass frame, with and without subtraction of the contribution of ϕ(1020) meson decays to the K− yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The ratio of K− to K+ energy spectra is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate that after inclusion of the ϕ meson decay contribution to the K− production no difference between the slopes of the K− and K+ energy spectra is observed within uncertainties. For our data a linear fit to this ratio obtained after subtraction of the ϕ meson contribution still shows a decrease with kinetic energy, although a constant value cannot be rejected. The contribution of Λ(1520)→pK− decays estimated from fitting the thermal model to the experimental yields appears to be another factor of moderate relevance.

International audience; The study of nuclei properties and of collision dynamics is a very active research field whose result have implications in different domains as for example astrophysics. The present and future facilities delivering radioactive ion beams with high intensity allow to extend these studies in the region far from the stability valley. New insight has thus been found on the effects of neutron richness on reaction mechanisms as well as on nuclear structure and nuclear matter properties, as for instance, the role of symmetry energy term of the nuclear Equation of State. The presence of diverse reaction products demands for highly performing and very specialized devices, also able to disentangle among different mechanisms, from fast dynamical processes to statistical emission from equilibrated sources. Numerous studies of the effects of N/Z ratio on fusion and associated processes can be found at different energies, together with many examples of the influence of neutron richness on the reaction time scale and the competition between equilibrated and prompt processes. A survey of very recent findings obtained with the CHIMERA and FARCOS devices is presented.

In nuclear reactions at Fermi energies two and multi particles intensity interferometry correlation methods are powerful tools in order to pin down the characteristic time scale of the emission processes. In this paper we summarize an improved application of the fragment-fragment correlation function in the specific physics case of heavy projectile-like (PLF) binary massive splitting in two fragments of intermediate mass(IMF). Results are shown for the reverse kinematics reaction 124 Sn+64 Ni at 35 AMeV that has been investigated by using the forward part of CHIMERA multi-detector. The analysis was performed as a function of the charge asymmetry of the observed couples of IMF. We show a coexistence of dynamical and statistical components as a function of the charge asymmetry. Transport CoMD simulations are compared with the data in order to pin down the timescale of the fragments production and the relevant ingredients of the in medium effective interaction used in the transport calculations.

As online trigger for events containing Λ hyperons in p+p collisions at 3.1 GeV a silicon-based device has been designed and built. This system has been integrated close to the target region within the FOPI spectrometer at GSI and was also employed as a tracking device to improve the vertex reconstruction of secondary decays. The design of the detector components, read-out, the trigger capability as well as the tracking performance are presented. An enrichment factor of about 14 was achieved for events containing a Λ-hyperon candidate.

The production of K$^+$, K$^-$ and $\varphi$(1020) mesons is studied in Al+Al collisions at a beam energy of 1.9A GeV which is close or below the production threshold in NN reactions. Inverse slopes, anisotropy parameters, and total emission yields of K$^{\pm}$ mesons are obtained. A comparison of the ratio of kinetic energy distributions of K$^-$ and K$^+$ mesons to the HSD transport model calculations suggests that the inclusion of the in-medium modifications of kaon properties is necessary to reproduce the ratio. The inverse slope and total yield of $\phi$ mesons are deduced. The contribution to K$^-$ production from $\phi$ meson decays is found to be [17 $\pm$ 3 (stat) $^{+2}_{-7}$ (syst)] %. The results are in line with previous K$^{\pm}$ and $\phi$ data obtained for different colliding systems at similar incident beam energies., Comment: 16 pages, 11 figures

Author(s): Cap, T; Siwek-Wilczynska, K; Wilczynski, J; Amorini, F; Auditore, L; Cardella, G; De Filippo, E; Geraci, E; Grassi, L; Grzeszczuk, A; La Guidara, E; Han, J; Kozik, T; Lanzalone, G; Lombardo, I; Najman, R; Nicolis, NG; Pagano, A; Papa, M; Piasecki, E; Pirrone, S; Planeta, R; Politi, G; Rizzo, F; Russotto, P; Skwira-Chalot, I; Trifiro, A; Trimarchi, M; Verde, G; Zipper, W

According to the model predictions, observation of toroidal objects is expected in collisions of heavy ion at low incident energies. Comparison between experimental data and model predictions which may indicate the formation of flat/toroidal nuclear systems is shown.

We analysed the $\phi$ meson production in central Ni+Ni collisions at the beam kinetic energy of 1.93A GeV with the FOPI spectrometer and found the production probability per event of $[8.6 ~\pm~ 1.6 ~(\text{stat}) \pm 1.5 ~(\text{syst})] \times 10^{-4}$. This new data point allows for the first time to inspect the centrality dependence of the subthreshold $\phi$ meson production in heavy-ion collisions. The rise of $\phi$ meson multiplicity per event with mean number of participants can be parameterized by the power function with exponent $\alpha = 1.8 \pm 0.6$. The ratio of $\phi$ to $\text{K}^-$ production yields seems not to depend within the experimental uncertainties on the collision centrality, and the average of measured values was found to be $0.36 \pm 0.05$., Comment: 9 pages, 5 figures

Using the large acceptance apparatus FOPI, we study central and semi-central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca + 40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni + 58Ni (0.15, 0.25, 0.4), 96Ru + 96Ru (0.4, 1.0, 1.5), 96Zr + 96Zr (0.4, 1.0, 1.5), 129Xe + CsI (0.15, 0.25, 0.4), 197Au + 197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include directed and elliptic flow. The data are compared to earlier data where possible and to transport model simulations. A stiff nuclear equation of state is found to be incompatible with the data. Evidence for extra-repulsion of neutrons in compressed asymmetric matter is found.

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 complete set of 27 excitation functions for synthesis of superheavy nuclei produced in cold fusion reactions was analyzed in terms of the "Fusion by Diffusion Model" of Światecki et al., modified to account for the angular momentum dependence of the fusion hindrance factor. The data on cold fusion reactions originate from experiments carried out at GSI Darmstadt, RIKEN Tokyo and LBNL Berkeley in which 208 Pb and 209 Bi targets were bombarded with the variety of projectiles ranging from 48,50 Ti to 70 Zn .

We present results of a new analysis of the experiment carried out by the REVERSE-ISOSPIN collaboration on the 124 Sn + 64 Ni reaction at the bombarding energy of 35 MeV/nucleon. The mass numbers of the intermediate mass fragments (isotopes of Be , B and C ) could be resolved in this experiment. Angular distributions of the neck fragmentation products in the rest frame of the primary projectile-like fragment were studied. The angular dependence of the isotopic ratios of the intermediate mass fragments proves the effect of neutron enrichment of the neck region.

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): Ca-40 + Ca-40 (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), Ni-58 + Ni-58 (0.15, 0.25, 0.4), Ru-96+Ru-96 (0.4, 1.0. 1.5), (96)zr+(96)zr 1.0, 1.5), Xe-129+CsI (0.15, 0.25, 0.4), Au-197 + Au-197 (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations. (C) 2010 Elsevier B.V. All rights reserved.

In the last decade some 20–30 publications in leading journals appeared in which cross sections for production of super-heavy elements are calculated with an erroneous formula for the Γn/Γf ratio. The erroneous treatment of shell structure corrections leads to an energy-dependent fission barrier that is inserted to the expression for the fission width Γf. In this approach the shell effect in the residual nucleus that emitted the neutron is ignored. We give examples of calculations that illustrate the deviations of the erroneous formula from the correct one. The errors reach several orders of magnitude, especially for low excitation energies and those compound nuclei for which large ground-state shell effect exceeds the neutron binding energy.

Detailed characteristics of a new reaction mechanism of fast ternary break-up in collisions of a heavy nucleus-nucleus system 197 Au + 197 Au at 15 MeV/nucleon, studied in experiments at the INFN LNS Laboratory in Catania by using the multidetector array CHIMERA are presented. Results of an analysis of mass and energy correlations complement our earlier report that demonstrated the mechanism of aligned re-separation of the Au + Au system into three massive fragments in semi-peripheral collisions.

Calculations of the evaporation-residue cross sections for production of super-heavy elements of Z = 114–118 in hot fusion (3n and 4n) reactions induced by 48 Ca projectiles on Pu , Am , Cm and Cf targets are presented. Results of calculations are compared with the cross sections measured by Oganessian et al. in the experiments in which the Z = 114–118 elements had been discovered. Calculations were done for the ground-state masses and fission saddle-point energies of Myers and Swiatecki and Sobiczewski et al. Considerable differences in the theoretical masses result in large differences (of several orders of magnitude) in the predicted cross sections. The ground-state masses and fission barriers of Sobiczewski et al. seem to well reproduce the experimental cross sections.

A set of 28 reactions of heavy and superheavy systems for which measured evaporation cross sections are available in the literature was analyzed with the aim to extract information on the fusion hindrance factor. Systematics of the deduced "experimental" hindrance factors (or in other words – fusion probabilities Pfus), based on the dependence of Pfus on the Coulomb interaction parameter [Formula: see text] and the excess of energy above the interaction barrier, E - B0, is presented.

By using well tested standard statistical model for calculating survival probabilities of super-heavy compound nuclei, Psurv, and reliably predicted capture cross sections σcap, "empirical" values of the fusion hindrance Pfus = σsyn/(σcap · Psurv) have been determined from the formation cross sections σsyn for production of super-heavy nuclei of 102 ≤ Z ≤ 113 measured at GSI Darmstadt and RIKEN. So determined fusion hindrance can be well reproduced with a simple model based on the Smoluchowski diffusion equation applied to describe thermal shape fluctuations of the fusing system. An applicability of this model for a wider class of fusing systems could be verified on data from an interesting experiment on the synthesis of isotopes of Hs (Z = 108) in the 136 Xe + 136 Xe reaction, scheduled to be carried out in Dubna this year. Synthesis cross sections for 269-271 Hs isotopes, strongly reduced by the fusion hindrance effect in this symmetric fusion reaction, are predicted.

Using the large acceptance apparatus FOPI, we study pion emission in the reactions (energies in A GeV are given in parentheses): 40Ca + 40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 96Ru + 96Ru (0.4, 1.0, 1.5), 96Zr + 96Zr (0.4, 1.0, 1.5), 197Au + 197Au (0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include longitudinal and transverse rapidity distributions and stopping, polar anisotropies, pion multiplicities, transverse momentum spectra, ratios ( π + / π − ) of average transverse momenta and of yields, directed flow, elliptic flow. The data are compared to earlier data where possible and to transport model simulations.

$\ensuremath{\phi}$ and ${\mathrm{K}}^{\ensuremath{-}}$ mesons from Ni+Ni collisions at the beam energy of $1.91A$ GeV have been measured by the FOPI spectrometer, with a trigger selecting central and semicentral events amounting to 52% of the total cross section. The phase-space distributions, and the total yield of ${\mathrm{K}}^{\ensuremath{-}}$, as well as the kinetic energy distribution and the total yield of $\ensuremath{\phi}$ mesons are presented. The $\ensuremath{\phi}/$ ${\mathrm{K}}^{\ensuremath{-}}$ ratio is found to be $0.44\ifmmode\pm\else\textpm\fi{}0.07{(\text{stat})}_{\ensuremath{-}0.10}^{+0.16}(\text{syst})$, meaning that about 22% of ${\mathrm{K}}^{\ensuremath{-}}$ mesons originate from the decays of $\ensuremath{\phi}$ mesons, occurring mostly in vacuum. The inverse slopes of direct kaons are up to about 15 MeV larger than the ones extracted within the one-source model, signaling that a considerable share of gap between the slopes of ${\mathrm{K}}^{+}$ and ${\mathrm{K}}^{\ensuremath{-}}$ could be explained by the contribution of $\ensuremath{\phi}$ mesons to negative kaons.

Collisions of a very heavy 197 Au + 197 Au system have been studied at an energy of 15 MeV/nucleon with the aim to investigate a possible change of the energy dissipation mechanism from one-body dissipation (presumably dominating at low excitation energies) to two-body dissipation. The experiment was carried out in 4π geometry using the CHIMERA multidetector array. A class of ternary events satisfying nearly complete balance of mass numbers was selected. Preliminary results suggest that the selected ternary events represent mostly prompt ternary partitions of the colliding system, in which the lightest fragment is quite massive. In the light of theoretical predictions of Cârjan, Sierk and Nix this result may imply that the observed ternary reactions are driven by the two-body dissipation mechanism already at 15 MeV/nucleon.

Analysis of existing data on experimental fission barriers for about 90 nuclei shows that the shell correction energy practically vanishes at the barrier configuration. Statistical model calculations, with shell effects accounted for by the Ignatyuk formula, were carried out for the decay of the 248 Cf compound nucleus assuming the ground state shell corrections of Möller et al., and the vanishing shell correction energy at the barrier. The results are consistent with existing experimental data on fusion- and xn evaporation-residue cross sections in the 12 C +236 U reaction.

New results on nuclear collective flow are presented for central and semi-central Ru + Ru collisions at 400 A MeV measured with the FOPI detector at GSI-Darmstadt. The source shape parameters, flow angle and aspect ratios, are extracted from Gaussian fits to in-plane and out-of-plane momentum distributions. The orientation and the shape of the source exhibit different trends according to the investigated phase space region. The shape parameters of the participant source are studied as a function of the particle mass and collision centrality. The flow angle is found to be independent of the particle mass. Both the flow angle and the aspect ratios depend sensitively on the impact parameter. Detailed comparisons with the predictions of the isospin quantum molecular dynamics model are performed. It is shown in particular that the source shape parameters permit to extract information on the in-medium nucleon–nucleon cross section.

The new detector CHIMERA, in its final 4π configuration, has been installed at Laboratori Nazionali del Sud (LNS) in Catania in January 2003. Beams of different energies ranging from protons to Au ions were delivered by the Tandem and the Super Conducting Cyclotron for nuclear reaction studies, in agreement with the approval of the Scientific Advisory Committee of LNS. Recent experimental results confirm very low energy thresholds of the trigger (below 0.5 MeV/nucleon), ensured within a wide dynamical range. Good characteristics of identification of light charged particles and heavy fragments have been obtained by using three detection techniques: Δ E-E , Δ E -time of flight, and the Pulse-Shape discrimination method. We present results of recent analysis concerning the production of intermediate mass fragments (IMF) in semi-peripheral collisions. Our results combined with theoretical Boltzmann-Nordheim-Vlasov simulations clearly demonstrate the presence of very fast processes of IMF production in the overlapping region of the target and projectile nuclei during re-separation, i.e. in the time scale comparable with the collision time. Evidence for slower, sequential-like production of IMF's is also shown.

Azimuthal emission patterns of $K^\pm$ mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum $p_{T}$ integrated directed and elliptic flow of $K^{+}$ and $K^{-}$ mesons as well as the centrality dependence of $p_{T}$ - differential directed flow of $K^{+}$ mesons are compared to the predictions of HSD and IQMD transport models. The data exhibits different propagation patterns of $K^{+}$ and $K^{-}$ mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for $K^{+}$ mesons and attractive for $K^{-}$ mesons.

Predictions of relatively large cross sections (of about 1 picobarn) for synthesis of super heavy nuclei of Z = 122 and Z = 124 in cold fusion (1n) reactions of symmetric 154Sm + 150Nd and 154Sm + 154Sm systems by R.K. Choudhury and Y.K. Gupta (2014) [1] are examined. The authors state that this result had been obtained by using the fusion-by-diffusion (FBD) model. As predictions of the original FBD model of Swiatecki, Cap, Siwek-Wilczynska and Wilczynski had been definitely pessimistic regarding fusion of more symmetric systems (in comparison with equivalent asymmetric systems), we feel compelled to present excitation functions of the 154Sm(150Nd, 1n)303122 and 154Sm(154Sm, 1n)307124 reactions, calculated within the original fusion-by-diffusion model. In accordance with our earlier predictions of a general trend of fusion hindrance for near-symmetric systems, the cross sections for synthesis of 303122 and 307124 nuclides in fusion of these two symmetric systems are found to be extremely small and probably never reachable: about 10 − 11 pb and 10 − 13 pb , respectively. It is shown that Choudhury and Gupta obtained their results (overestimating the cross sections by 11 and 13 orders of magnitude) as an effect of an arbitrary and physically unjustified interference in the FBD model.

Experimental data on charged kaon phase space distributions and strangeness sideward flow measured with the FOPI detector at SIS/GSI are presented. Comparisons are made with the predictions of transport models investigating the in-medium kaon-nucleon potential.

Small-angle correlations of pairs of nonidentical light charged particles produced in central collisions of heavy ions in the A= 100 mass region at a beam energy of 400 A· MeV are investigated with the FOPI detector system at GSI Darmstadt. The difference of longitudinal correlation functions with the relative velocity parallel and anti-parallel to the center-of-mass velocity of the pair in the central source frame is studied. This method allows extracting the apparent space-time differences of the emission of the charged particles. Comparing the correlations with results of a final-state interaction model delivers quantitative estimates of these asymmetries. Time delays as short as 1~fm/c or – alternatively – source radius differences of a few tenth fm are resolved. The strong collective expansion of the participant zone introduces not only an apparent reduction of the source radius but also a modification of the emission times. After correcting for both effects a complete sequence of the space-time emission of p, d, t, 3He, α particles is presented for the first time.

We present new experimental results concerning the azimuthal distributions of proton-likes, light and intermediate mass fragments at midrapidity for Au(100-800 AMeV)+Au collisions measured with the FOPI phase-I detector at GSI in Darmstadt. The azimuthal distributions are investigated as a function of the collision centrality, the incident energy, the fragment charge and transverse momentum. The azimuthal anisotropy is maximum for impact parameters around 7 fm. Intermediate mass fragments present a stronger out-of-plane emission signal than light fragments and a saturation is reached for Z greater than or equal to 4. The azimuthal anisotropy increases with the fragment transverse momentum and decreases as the incident energy increases. The azimuthal anisotropy of Z = 2 particles investigated as a function of the scaled fragment transverse momentum follows an universal curve for bombarding energies between 250-800 AMeV. A signature for a transition from in-plane to out-of-plane emission is evidenced at the lowest beam energies.

Charged pions are measured with the 4π detector FOPI at GSI using the Au on Au reaction at 1.06 AGeV bombarding energy. The pion multiplicities ngp increase with the number of participants Apart. The average pion multiplicities per participant are #### and #### These values are only half as large as extrapolated from the low-mass systems studied by Harris et al. The ratio #### increases with Apart and decreases with the pion kinetic energies. The pion kinetic energy spectra have concave shapes, their parametrization in terms of thermal Boltzmann distributions yields a low (T l,π) and high (Th,π) temperature which change with the cm emission angle Θ of the pions. In the angular range 45dg is larger than , the high temperatures , are, within experimental uncertainties, the same. The inclusive polar angular distributions of pions are anisotropic, dσ/dΩ increases for forward and backward angles. The forward — backward enhancements are independent of the pion kinetic energies or the number of participants. In addition to the preferred forward — backward emission, also the enhanced emission into the transverse direction Θ = 90° is observed for pions with high energies or for pions from near-central collisions. These observations and the shape of the rapidity spectra suggest that pions, emitted from the central rapidity region, are partly rescattered by spectator matter. The strength of the rescattering process depends only weakly on the number of participants. The experimental data are compared to the results of IQMD/GEANT calculations using momentum dependent NN interactions and a hard equation of state. The calculated pion multiplicities are approximately 50% larger than experimentally determined; the existence of secondary pion sources is reproduced by the calculation, but their predicted strengths are larger than experimentally observed.

Collisions of Au on Au at incident energies of 150, 250 and 400 A MeV were studied with the FOPI-facility at GSI Darmstadt. Nuclear charge (Z < 16) and velocity of the products were detected with full azimuthal acceptance at laboratory angles of 1-30 degrees. Isotope separated light charged particles were measured with movable multiple telescopes in an angular range of 6-90 degrees. Central collisions representing about 1 % of the reaction cross section were selected by requiring high total transverse energy, but vanishing sideflow. The velocity space distributions and yields of the emitted fragments are reported. The data are analysed in terms of a thermal model including radial flow. A comparison with predictions of the Quantum Molecular Model is presented., LateX text 62 pages, plus six Postscript files with a total of 34 figures, accepted by Nucl.Phys.A

In past experiments, mass asymmetric projectile-target combinations 124Sn+64Ni and 112Sn+58Ni were investigated at ELab(112,124Sn)=35 A.MeV beam energy by using the 4π multi-detector CHIMERA. From a quantitative comparison of cross sections associated to Statistical and Dynamical Fission of the Projectile-Like Fragments, it resulted that Dynamical Fission process is about two times more probable in the neutron rich 124Sn+64Ni system than in the 112Sn +58 Ni neutron poor one. In contrast, no sizable difference was found for Statistical Fission mechanism. The observed difference in the strength of the Dynamical effects could arise from the difference in entrance channel Isospin (N/Z) content. In order to disentangle Isospin effects from effects due to the different masses of the two systems, a new experiment 124Xe+64Zn at 35 A.MeV beam energy has been recently carried out.

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.

Projectile-like fragments (PLF's) emitted in damped collisions of 15 MeV/u 20Ne ions with 197Au were observed in coincidence with two fission fragments. For given detection angles of the PLF's differential and energy-integrated fission probabilities were obtained and the average missing momentum vectors were deduced by using improved analysis methods of the fission fragment angular correlation. The average missing momentum vectors were found to point in the direction of the observed PLF, with a systematic deviation towards beam direction for larger mass transfers. The missing momentum thus appears to mainly originate from the sequential decay of the PLF's.

We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at midrapidity in semiperipheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $\ensuremath{\langle}N/Z\ensuremath{\rangle}$ isospin asymmetry, stronger angular anisotropies, and reduced odd-even staggering effects in neutron to proton ratio $\ensuremath{\langle}N/Z\ensuremath{\rangle}$ 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 quasispectator 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.

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).

An interesting process of violent reseparation of a heavy nuclear system into three or four fragments of comparable size was recently observed in {sup 197}Au+{sup 197}Au collisions at 15 MeV/nucleon. Combined analysis of the binary deep inelastic events and the ternary and quaternary breakup events demonstrates that the newly observed ternary and quaternary reactions belong to the same wide class of deep inelastic collisions as the conventional (binary) damped reactions. It is shown that the ternary and quaternary breakup reactions occur at extremely inelastic collisions corresponding to small impact parameters, while more peripheral collisions lead to well-known binary deep inelastic reactions.

The K{sup 0} meson production by {pi}{sup -} mesons of 1.15 GeV/c momentum on C, Al, Cu, Sn, and Pb nuclear targets was measured with the FOPI spectrometer at the Schwer-Ionen-Synchrotron accelerator of GSI. Inclusive production cross sections and the momentum distributions of K{sup 0} mesons are compared to scaled elementary production cross sections and to predictions of theoretical models describing the in-medium production of kaons. The data represent a new reference for those models, which are widely used for interpretation of the strangeness production in heavy-ion collisions. The presented results demonstrate the sensitivity of the kaon production to the reaction amplitudes inside nuclei and point to the existence of a repulsive KN potential of 20{+-}5 MeV at normal nuclear matter density.

First measurement of subthreshold {sigma}(1385) production is presented. Experimental data are presented for Al+Al reactions at 1.9A GeV measured with the FOPI detector at SIS/GSI. The {sigma}(1385)/{lambda} ratio is found to be in good agreement with the transport and statistical model predictions. The results allow for a better understanding of subthreshold strangeness production and strangeness exchange reaction which is the dominant process for K{sup -} production below and close-to threshold.

Collisions of a very heavy nuclear system, 197 Au + 197 Au , were studied at the energy of 15 MeV/nucleon with the aim to identify and investigate main macroscopic modes of re-separation of such a heavy nuclear system. The experiment was performed at the INFN LNS laboratory in Catania by using the multidetector array CHIMERA. Along with binary strongly damped collisions, a strong component of a new re-separation mode: the "fast ternary fission" in characteristic nearly co-linear configuration was observed and the time scale of this process was determined.

Multi-breakup processes for the {sup 124}Sn+{sup 64}Ni system at 35 MeV/nucleon have been studied with the forward part of the CHIMERA detector. An extensive comparison between experimental data corresponding to almost complete ternary events and constrained molecular dynamics (CoMD-II) calculations suggests different characteristic times in the selected processes. This is in agreement with previous studies of the same reaction already published concerning the prompt intermediate-mass-fragment emission. Stimulated by CoMD-II calculations, we investigate the existence of more complex dynamical multi-breakup processes occurring on the same time scale. A detailed study of the rotational dynamics leading to slower dynamical fission processes is also presented.

Results on $K^+$ and $K^0$ meson production in $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr collisions at a beam kinetic energy of 1.528$A$ GeV, measured with the FOPI detector at GSI-Darmstadt, are investigated as a possible probe of isospin effects in high density nuclear matter. The measured double ratio ($K^+/K^0$)$_{Ru}$/($K^+/K^0$)$_{Zr}$ is compared to the predictions of a thermal model and a Relativistic Mean Field transport model using two different collision scenarios and under different assumptions on the stiffness of the symmetry energy. We find a good agreement with the thermal model prediction and the assumption of a soft symmetry energy for infinite nuclear matter while more realistic transport simulations of the collisions show a similar agreement with the data but also exhibit a reduced sensitivity to the symmetry term.

New results concerning the production of neutral strange particles, $K^0$ and $\Lambda$ in Ni + Ni collisions at 1.93$A$ GeV, measured with the FOPI detector at GSI-Darmstadt, are presented. Rapidity density distributions and Boltzmann slope parameter distributions are measured in nearly the full phase space of the reaction. The observables are compared to existing $K^+$ and proton data. While the $K^0$ data agree with previously reported $K^+$ measurements, the $\Lambda$ distributions show a different behavior relative to that of protons. The strangeness balance and the production yield per participating nucleon as a function of the centrality of the reaction are discussed, for the first time at SIS energies., Comment: 10 pages, 8 figures

Ternary events originating from the 197 Au + 197 Au reaction at 15 MeV/nucleon, studied by using the multidetector array CHIMERA at LNS Catania, have been collected in almost complete 2π range of the forward hemisphere of CHIMERA thus extending the angular range of our previously reported preliminary data. Energy- and time calibrations for heavy fragments at large angles were supplemented with an analysis of coincidence events of binary strongly damped reactions. Contrary to the previous preliminary results, the new complete data clearly show presence of sequential fission processes in which one of Au -like nuclei undergoes fission after re-separation of the primary binary system. Mechanism of these two types of reactions observed in our data, sequential fission reactions and prompt ternary processes, are presently studied using comparisons with predictions of the stochastic BNV model of Baran, Colonna and Di Toro and the QMD model of Łukasik.

T. Cap1∗, K. Siwek-Wilczynska1, I. Skwira-Chalot1, J. Wilczynski2, F. Amorini3,4, L. Auditore5, G. Cardella6, E. De Filippo6, E. Geraci4,6, L. Grassi4,6, A. Grzeszczuk7, E. La Guidara8, J. Han3, T. Kozik9, G. Lanzalone3,10, I. Lombardo11, R. Najman9, N. G. Nicolis12, A. Pagano6, M. Papa6, E. Piasecki2,13, S. Pirrone6, R. P laneta9, G. Politi4,6, F. Rizzo3,4, P. Russotto3,4, A. Trifiro5, M. Trimarchi5, G. Verde6 and W. Zipper7