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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.

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.

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.

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.

We report on the status of the Time-of-Flight upgrade with M ultistrip- M ultigap- R esistive- P late- C hambers (MMRPCs) for the FOPI detector at GSI [J.L. Ritman and the FOPI collaboration: Nucl Phys. B – Proc. Supp. 44 (1995) 708–715 ]. Final detector parameters for the mass production of the counters and the electronic readout system are presented. These final parameters are based on measurements which took place over the last years where the operating range of the MMRPCs has been mapped out with respect to time resolution, efficiency and cluster size. For this purpose we show results at different beam intensities, electric fields and at different preamplifier gains (FEE-gain).

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 characteristics of a symmetric multigap resistive plate chamber with multistrip readout electrode, recently developed by us, continued to be investigated. Studies of the time resolution, efficiency, average charge and dark rate as a function of applied voltage and the influence of the angle of incidence of the detected particle on these observables have been performed. Different type of discriminators have been tested.

A completely new configuration of a glass resistive-plate chamber (GRPC) was built and tested. It consists of a double two-gap structure of electrodes with an active area of about 400 cm 2 and is read out via a central multistrip printed circuit board. In measurements with a 60 Co source and p, d particles of 1.5 A GeV time resolutions better than 80 ps , position resolution along the strips of 5– 6 mm and efficiencies larger than 95% were obtained using available fast standard electronics. These results open the possibility of constructing compact TOF detectors of high resolution and high granularity.

A spark counter of the type developed by Pestov has been tested with the aim of searching for an optimum time response function, changing voltage, content of noble and quencher gases, pressure and energy-loss. Replacing the usual argon by neon has brought an improvement of the resolution and a significant reduction of tails in the time response function. It has been proven that a counter as long as 90 cm can deliver, using neon gas mixture, a time resolution σ ps with about 1% absolute tail and an efficiency of about 90%.

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.

Light-particle emission from Au+Au collisions has been studied in the bombarding-energy range 100–250 A ·MeV, using ΔE − E R telescopes in coincidence with the FOPI detector in its phase I configuration. Center-of-mass energy spectra have been measured for Z = 1,2 isotopes emitted in central collisions at CM polar angles between 60° and 90°. Evidence for a collective expansion is reported, on the basis of the mean kinetic energies of hydrogen isotopes. Comparison is presented with statistical calculations (WIX code). For CM kinetic energy spectra, fair agreement is found between data and a recently developed transport model.

R Crochet a, F. Rami a, R. Don~. a'b, J.R Coffin a, R Fintz a, G. Guillaume ~, F. Jundt a, C. Kuhn a, C. Roy a, B. de Schauenburg a, L. Tizniti ~, E Wagner a, J.E Alard c, A. Andronic d, Z. Basrak e, N. Bastid c, I. Belyaev f, A. Bendarag c, G. Berek i, D. BestL J. Biegansky h, A. Buta J, R. (~aplar e, N. Cindro e, E Dupieux c, M. D2elalija e, Z.G. Fan ~, Z. Fodor i, L. Fraysse ~, R.P. Freifelder g, A. Gobbi g, N. Hermlann g, K.D. Hildenbrand g, B. Hong g, S.C. Jeongg, J. Kecskemeti i, M. Kirejczyk j, P. Koncz i, M. Korolija e, R. Kotte h, A. Lebedev f'k, Y. Leifels g, V. Manko k, D. Moisa ~, J. M6sner n, W. Neubert h, D. Pelte e, M. Petrovici d, C. Pinkenburgg, W. Reisdorfg, J.L. Ritman g, A.G. Sadchikov k, D. Schtill g, Z. Seres i, B. SikoraJ, V. Simion a, K. Siwek-Wilczyfiska j, U. Sodan g, K.M. Teh g, M. Trzaska ~', G.S. Wang g, J.P. Wessels g, T. Wienold g, K. Wisniewski g, D. Wohlfarthh A. Zhilin f FOPI Collaboration, C. Hartnack m

The binary and ternary products from reactions of 238U beams with targets of 16O, 27Al, 48Ca, 45Sc, 48Ti, 58Fe, 64Ni and 89Y have been recorded at 6.0 MeV/u bombarding energy with four position-sensitive avalanche detectors, operated in coincidence. A few runs at 5.4 MeV/u have also been performed. Accurate triple-differential cross sections, d 3 σ d A d θ c.m. dTKE , are obtained for the binary events within the full range of mass A and total kinetic energy TKE, and within almost the full range of center-of-mass angle θc.m.. Similar cross sections are obtained with somewhat less accuracy for triple events stemming from the sequential fission of uranium-like products. The distributions are discussed in terms of quasielastic and strongly damped scattering, where the products have partially relaxed energies and negligible average drift in mass, as opposed to capture where the products emerge with fully relaxed energies after a more or less pronounced mass drift towards symmetry. Apart from the reaction with 16O, all the capture product distributions are dominated by the non-equilibrium quasi-fission (or fast fission) process. The central feature of this reaction mechanism is the evolution of the reaction complex towards mass symmetry. With the 27Al target the evolution towards symmetry is almost complete, whereas the heavier targets show very broad mass distributions with clear evidence of dissociation taking place before symmetry is reached. At the same time, the cross section for quasi-fission diminishes as the target Z-value increases. With the 89Y target the strongly damped scattering component dominates completely. The capture cross sections are discussed in terms of the extra-push concept, and the mass and angular distributions in quasi-fission are analyzed in terms of interaction time and mass rearrangement as functions of target Z-value and excess kinetic energy in the entrance channel.

At a bombarding energy of 14.7 MeV/u the charge, mass and angular distributions have been measured as a function of energy loss for reaction products induced by 98 Mo and 92 Mo projectiles on targets of 98 Mo, 147 Sm, 154 Sm and 92 Mo, 154 Sm, 238 U, respectively. An analysis of the product distributions shows the presence of a non-equilibrium sharing of the excitation energy, an exponential growth of the charge and mass variances, a complete N Z equilibration and a large yield of non-binary complex fragments. Monte Carlo simulations are found to be an indispensable tool of the analysis.

Reactions of 132Xe with 56Fe were studied at 5.0, 5.7 and 8.5 MeV/u by means of ΔE − E ionisation chambers. Aside from quasi-elastic and deep-inelastic reaction products a group of fully relaxed fragments with a symmetric Z-distribution centered at half the atomic number of the combined system was observed at all incident energies. The angular distribution for each element in this group exhibits a 1 sin θ dependence. These reaction products are ascribed to capture processes leading either to compound-nucleus or to fast fission. The energy dependence of the capture cross section is compared with various models.

Evaporation-residue excitation functions for the reactions 86 Kr + 70,76 Ge, 92,100 Mo, 99,102,104 Ru have been measured using activation methods and the velocity filter SHIP. The data span the region from well below the fusion barrier up to, and beyond, the energy where limitation by fission competition takes place. The data are shown to be compatible with the concept of complete fusion followed by the statistical decay of the equilibrated compound nucleus. Information on both the fusion probability at and below the fusion threshold and the fissionability of the compound nuclei formed, is extracted. The model dependence of the extracted fission barriers is discussed in detail. In analogy to studies involving lighter projectiles, strong correlations between the low-energy nuclear-structure properties of the nuclei and the subbarrier fusion probability are found. A relative shift of the fusion barrier to higher energies, that increases with the number of valence neutrons in the target nuclei, is observed.

An inclusive measurement of light and medium heavy fragments for eight projectile target combinations and incoming energies is presented. The energy spectra of all fragments are fitted consistently with a moving source parametrization. The results are compared to several model predictions. No evidence for the liquid gas phase transition of nuclear matter is found and considerable doubts in thermal interpretations arise. An alternative model of a cold shattering of the target nucleus is able to explain the energy spectra well but fails to reproduce the charge spectra.

The mass and charge of fragments produced in deep inelastic reactions induced by 236 MeV 40 Ar on targets of 42, 48 Ca, 50 Ti. 50 Cr, 56 Fe and 60 Ni were identified by using a time-of-flight ΔE - E detector telescope. The measured nuclide distributions are very broad along the mass asymmetry coordinate, but narrow along the charge asymmetry coordinate. A detailed description of the variations of the mass and charge distributions as a function of target neutron excess is obtained by calculating primary distributions assuming a diffusion-like mass transfer in a two-dimensional potential energy surface determined by liquid drop energies of two touching spheres and folding this primary distribution with the secondary particle decay pattern calculated in the statistical model. Exotic nuclei are produced with comparatively large cross sections.

A kinematically complete study of the symmetric systems 144Sm+144Sm and 154Sn+154Sm has been performed at energies 30% in excess of the interaction barrier. They have been chosen because of their different internal structure: 144Sm has a closed N = 82 neutron shell and a spherical ground-state configuration; 154Sm with ten neutrons outside this shell is strongly deformed. The observed gross features of both reactions like energy, angular and total mass or element distributions are very similar; the ratio of the mass variances as function of the total kinetic energy loss indicates the number of exchanged nucleons to be comparable in all stages of the reactions. At small energy losses, however, the element distributions of the 144Sm + 144Sm reaction are considerably broader, pointing at an enhanced proton transfer at the cost of the number of exchanged neutrons in this system. This observation is attributed to the influence of the closed shell which seems to block the transfer of neutrons at low excitation energies. These results can be explained quantitatively by the different gradients of the shell-corrected potential energy surfaces of the two systems.

Fission fragment yields have been measured as a function of fragment mass, angle and energy for the 238 U + 16 O, 27 Al fusion reactions at 6 MeV/u. The observed anisotropies for the two systems indicate that a large fraction of the 238 U + 27 Al cross section is associated with the quasi-fission (or fast fission) reaction, whereas the 238 U + 16 O data are consistent with compound nucleus formation, followed by fission.

Complex fragments of 3 Z ⪅35 have been detected in the reverse-kinematics reactions of 93 Nb plus 9 Be, 12 C and 27 Al at bombarding energies of E / A =11.4, 14.7 and 18.0 MeV. Velocity spectra and angular distributions show the presence of projectile and target-like components along with a component isotropic (in the reaction plane). This latter component aappears as a Coulomb ring in the invariant cross section plots indicating the presence of a binary decay which is confirmed by the coincidence data. Statistical model calculations indicate that for the Nb+Be and C reactions, the isotropic component is associated with the binary decay of compound nuclei formed in complete fusion reactions. The charge distributions for these two systems are consistent with the conditional barriers predicted with the rotating finite-range model. For the Nb+Al reactions, there is an additional isotropic component besides compound nucleus decay, which may arise from fast fission.

The dynamics of heavy-ion collisions is studied experimentally for metastable composite systems with interaction times between the collision time of quasi- and deep-inelastic processes and the capture time of fast-fission and compound-nucleus-fission reactions. Detailed angular, total kinetic energy and mass distributions are measured for reaction products with masses between the target and projectile masses including the symmetric masses. The mass drift is observed as a function of total kinetic energy and scattering angle.

We present some inclusive data and a few coincident results obtained for the 129 Xe + nat Ag, 197 Au systems at 23.7 MeV/u and 27 MeV/u at GANIL. The reaction products have been detected between 5 and 13° in the laboratory. In addition to fragmentation products, we found products with kinetic energies, atomic numbers and masses substantially smaller than those of the projectile. We have studied different possibilities for their formation and are led to conclude that they are coming from interactions where three or more nuclei of significant size are present after the collision. It is likely they are coming from successive binary decays and we discuss different possibilities for such processes.

Fusion excitation functions for the systems 40 Ar + 112, 116, 122 Sn and 40 Ar + 144, 148, 154 Sm have been determined, covering cross sections ranging from several hundred mb down to the μb level. The data show a pronounced correlation of the subbarrier behaviour with low-energy collective properties of the nuclei involved and are well reproduced by simplified coupled-channel calculations coupling fusion to inelastic channels. The possibilities of parameterizing the data in terms of a simple dynamic barrier-fluctuation phenomenon are discussed and result in the prediction of remarkably diffuse partial-wave distributions above the barrier. This is shown to be important for the analysis of deexcitation phenomena following fusion reactions.