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The traditional isoscaling technique has been used to analyze all isotopically identified particles from 70 Zn+ 70 Zn and 64 Zn+ 64 Zn collisions at 35 MeV/u. Two additional techniques, using an energy-averaged ratio and using the data present in the tail of energy spectra, are compared to the traditional method and show similar results. Isoscaling fit parameters α and β are found both globally and for each individual series of constant Z and N . The data are then split up between emitted fragments and projectile-like fragments. Isoscaling values for the two different types of fragments are shown to be different, emphasizing the importance of experimentally distinguishing between projectile-like fragments and emitted fragments in order to achieve accurate isoscaling parameters.

Symmetry energy, temperature and density at the time of the intermediate mass fragment formation are determined in a self-consistent manner, using the experimentally reconstructed primary hot isotope yields and anti-symmetrized molecular dynamics (AMD) simulations. The yields of primary hot fragments are experimentally reconstructed for multifragmentation events in the reaction system Zn 64 + Sn 112 at 40 MeV / nucleon . Using the reconstructed hot isotope yields and an improved method, based on the modified Fisher model, symmetry energy values relative to the apparent temperature, a sym / T , are extracted. The extracted values are compared with those of the AMD simulations, extracted in the same way as those for the experiment, with the Gogny interaction with three different density-dependent symmetry energy terms. The a sym / T values change according to the density-dependent symmetry energy terms used. Using this relation, the density of the fragmenting system is extracted first. Then symmetry energy and apparent temperature are determined in a self consistent manner in the AMD model simulations. Comparing the calculated a sym / T values and those of the experimental values from the reconstructed yields, ρ / ρ 0 = 0.65 ± 0.02 , a sym = 23.1 ± 0.6 MeV and T = 5.0 ± 0.4 MeV are evaluated for the fragmenting system experimentally observed in the reaction studied.

Isoscaling is derived within a recently proposed modified Fisher model where the free energy near the critical point is described by the Landau O ( m 6 ) theory. In this model m = N f − Z f A f is the order parameter, a consequence of (one of) the symmetries of the nuclear Hamiltonian. Within this framework we show that isoscaling depends mainly on this order parameter through the ‘external (conjugate) field’ H. The external field is just given by the difference in chemical potentials of the neutrons and protons of the two sources. To distinguish from previously employed isoscaling relationships, this approach is dubbed: m-scaling. We discuss the relationship between this framework and the standard isoscaling formalism and point out some substantial differences in interpretation of experimental results which might result. These should be investigated further both theoretically and experimentally.

A very brief summary Of Our Current research on clustering in low density matter formed in near Fermi energy heavy ion collisions is presented. At the lowest densities and temperatures large alpha mass fractions are observed. Temperature and density dependent symmetry free energies have been derived from isoscaling analyzes of the yields of nuclei with A = 4. The symmetry free energies are far above those obtained in common effective interaction calculations, reflecting cluster formation, primarily of alpha particles, not included in such calculations.

We review the main results obtained by the BRAHMS collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so called quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e. the proposed Color Glass Condensate., 32 pages, 18 figures

The excitation energy deposited in the reaction 209 Bi(α,α′) at 240 MeV has been determined using the TAMU Neutron Ball. The reconstructed average excitation energies as a function of the beam energy losses show that not all of the missing beam energy is usually deposited as thermal excitation in the target nucleus. Requiring an additional coincidence with a light charged particle or fission fragment leads to selection of a significant higher average excitation energy. This effect is extrapolated to explore results of previous GDR decay measurements in the case of a 208 Pb target.

We have undertaken a study of the thermal and the dynamical properties of fission and evaporation processes through the observation of neutron and light charged particle (LCP) emission (p, α) in collisions of 20 Ne + 159 Tb and 20 Ne + 169 Tm at 8, 10, 13 and 16 MeV/nucleon using the neutron multidetector DEMON. Both systems lead to the formation of compound nuclei (CN) with initial excitation energies ( E x * ) ranging between 100 and 250 MeV. These CN, formed through complete (CF) or incomplete (IF) fusion reactions, decay through either fission or evaporation residue (ER) formation. Our experimental goal in this study is to establish, as a function of E x * , i) σ ER /σ fission cross-section ratios, ii) pre- and post-scission neutron and LCP multiplicities with a clear cut assignment to CF and IF processes and iii) to try to consistently interpret these data in the framework of the recently modified statistical code GEMINI, including time-dependent fission width probabilities in order to establish the fission time scales.

Neutron fold distributions measured for the reaction 209 Bi(α,α′) at 240 MeV have been analyzed with the help of Statistical Model calculations to determine the distribution of excitation energy, E x , in the primary target fragments as a function of the projectile energy loss, EL. The reconstructed distributions in excitation energy feature a plateau which extends from the kinematical limit E x = EL to very small excitations, indicating a variety of interactions of the beam particles with the target nucleus. The requirement of an additional coincidence with a light charged particle leads to the selection of a significant higher average excitation energy. Those results are extrapolated to explore the effects of including the excitation energy distributions in the analysis of previous GDR measurements in 208 Pb. Corrections of the derived GDR parameters due to the partial transfer of excitation energy are suggested.

Neutron fold distributions measured for the reaction 209 Bi(α,α′) at 240 MeV have been analyzed with the help of Statistical Model calculations to determine the distribution of excitation energy in the primary target fragments as a function of the projectile energy loss, EL. Results show that the distributions in excitation energy feature a plateau which extends from the kinematical limit E x =EL to very small excitations, suggesting a variety of interactions of the beam particles with the target nucleus. Requiring an additional coincidence with a light charged particle leads to selection of a significant higher average excitation energy. This effect is extrapolated to explore results of previous GDR decay measurements in the case of a 208 Pb target. Corrections of derived GDR parameters due to the partial transfer of excitation energy are suggested.

The pre-scission and post-scission multiplicities of alpha particles were determined in coincidence with fission fragments for four windows of exit channel mass asymmetry in the reaction 20Ne+165Ho at 50A MeV. The technique used employed a kinematic analysis of the energy spectra of alpha particles as a function of the emission angle with respect to the fission axis. Using a procedure of fitting the experimental energy spectra with those resulting from a Monte Carlo simulation program, the total multiplicity of alpha particles was separated into pre-scission and post-scission components. Using the pre-scission and post-scission multiplicities, neutron multiplicity measurements and other empirical observations, both the initial excitation energy and the excitation energy at scission of the compound nucleus were determined. The pre-scission times in the de-excitation of a highly excited 178W compound nucleus with initial excition energy of 570 MeV were evaluated using statistical model calculations. Only a small decrease in scission time was derived for the most asymmetric events studied. The possible contribution of very damped deep inelastic processes is discussed.

Nucleus-nucleus reaction mechanisms at incident energies below 10 MeV/u are governed by mean field effects. Nucleon-nucleon collisions begin to become important as the energy increases above the Fermi energy. This evolution manifests itself experimentally in the modification of the directed flow of the emitted participant (mid-rapidity) nucleons. In the reaction plane, it is expressed by the flow parameter [1]. Another aspect lies in the azimuthal distribution of particles relative to the reaction plane. At high energies, a maximum in the direction perpendicular to the reaction plane on both sides was named squeeze-out-effect [2]. Conversely, below 100 MeV/u, maxima in the reaction plane have been observed for the light systems of Ar + V : rotation-like effect [3]. It was studied as a Function of energy, impact parameter and emitted particle mass in the collisions of Ar-40 on Al-27 at energies from 36 to 65 MeV/u [4]. The latter study has been extended up to 95 MeV/u and measurements have been made for the Zn-64 + Ni-58 system at 5 energies from 35 to 79 MeV/u.

The multiplicities of γ-rays emitted in the giant dipole resonance decay of 200 Pb have been measured in coincidence with both evaporation residues and fission fragments. The experimental data have been compared with results of statistical calculations which take into account dynamical fission hindrance. The fission probability distribution has been determined as a function of excitation energy.

Light-particle emission from the fission reactions of 63Cu + 92,100Mo and 20Ne + 144,148,154Sm has been studied using the Texas A&M Neutron Ball detector. Linearmomentuum transfers (LMT) were determined from fission-fragment-folding-angle measurements. An increase of neutron multiplicity with apparent linear-momentum transfer was seen. The initial excitation energies of the compound nuclei are estimated from the observed linear-momentum transfer and also reconstructed from the measured multiplicities and average energies of neutrons, protons and α-particles. The results of the two methods are in good agreement. The observed neutron multiplicities show a strong increase with increasing neutron-to-proton ratio of the composite system. The light-particle multiplicities are compared with calculated values using the statistical code GEMINI. The effect of the dynamic fission delay on the total light-particle multiplicities is explored and found to be small.

The particle and gamma decay from 142Nd nuclei produced at E ∗ = 150 MeV by 16O + 126Te and 22Ne + 120Sn reactions were studied. The measured gamma ray spectra were analyzed to derive the GDR centroid and width parameters, which were found to be the same for both systems. No entrance channel effects were seen in the particle and gamma emission spectra in these systems.

Shapes consisting of a series of pear-like bodies surrounding an inner joined sphere are assumed to be those associated with symmetric fission or fragmentation into two or more fragments. The shapes evolve smoothly from that of an initial spherical nucleus to the scission point. The shapes are calculated using a generalization of the cassinian ovaloid shape parameterization, which has been demonstrated to be a good approximation for binary fission. Using this parameterization, fission barriers have been calculated for 2-, 3-, 4-, 6- and 8-fold multi-fragment final states. Proximity effects are included. The temperature dependence of these fission barriers is also calculated. The importance of nuclear dynamics in determining the range in which static barriers are sampled is discussed.

The emission of intermediate mass fragments (IMFs) has been studied using the 4π array, AMPHORA. The energy spectra, the angular distributions, the multiplicities, and the charge distributions are studied inclusively as well as in coincidence with projectile-like fragments (PLFs) and other fragments. The low-energy component of the inclusive fragment spectra can be reproduced by a statistical binary decay code GEMINI, although the calculated absolute cross sections are an order of magnitude smaller than the experimental IMF cross sections. At intermediate angles the fragments are dominated by IMFs with Z ≤ 10 both for inclusive and coincidence events and the energy spectra of the fragments show hard components which cannot be explained as statistical emission. For this non-equilibrium component strong azimuthal angular correlations are observed in IMF-PLF and IMF-IMF coincidence events. Both the energy spectra and the azimuthal angular correlations of the non-equilibrium component are well reproduced by an extended classical dynamical model.

Properties of medium mass nuclei having excitation energies of 1.5 to 6 MeV/u have been probed in measurements of the multiplicities and energy spectra of emitted particles and fragments. The particle spectra indicate a progressive reduction of both the level density parameter, a, and the emission barriers as the excitation energy is increased. The evolution of the dominant de-excitation modes, observed with increasing excitation energy, is found to be qualitatively consistent with the predictions of statistical models. There is, however, evidence that dynamics may play an important role in fragment emission processes. At energies of 6 MeV/u multifragment emission is an important process. Varying theoretical models predict such multifragment events but differ in their predictions of the probability of such events.

Energy spectra of light charged particles (Z = 1,2) observed at θLP = 5°−150° in coincidence with fragments of Z = 5–14 at θF = ±9° are examined. The fragment-energy spectra show two components, one with a projectile-like velocity and another with a much lower velocity. Light particles in coincidence with fragments of projectile-like velocity show a very strong left-right asymmetry in the forward hemisphere. At very forward angles the asymmetry is essentially dominated by a recoil effect of the ejectile emitted from the fragment. The asymmetry at intermediate angles (27°⩽ θ ⩽ 60°) shows a strong dependence on the charge of the fragments and the asymmetry is similar among those for the composite particles, whereas the asymmetry is much smaller for protons. Light particles in coincidence with the lower-energy component of the fragment spectra show much less asymmetry. For such fragments α-particle energy spectra are reproduced without an intermediate-velocity source of high apparent temperature, whereas this high temperature source is needed for the proton spectra. These facts may indicate that the dominant emission mechanism of the intermediate-velocity protons and α-particles is different. Possible mechanisms for the production of these particles are discussed.

Inclusive energy spectra and angular distributions for heavy ions (Z ≧ 3) produced in the reactions of 227 MeV and 310 MeV 16 O with Ti were measured. Also measured at the projectile energy of 310 MeV were energy and angular correlations between light charged particles ( Z ≦ 2) and heavy ions. From comparisons with statistical model calculations upper limits to the complete fusion cross sections of 647 mb and 265 mb were derived for projectile energies of 227 MeV and 310 MeV, respectively. At 310 MeV the cross section of incomplete fusion processes was estimated to be over 505 mb. Emission of fast, high-energy α-particles and protons was observed to be a characteristic feature of quasi-elastic, deep-inelastic and fusion-like reactions. Average multiplicities of fast light particles in coincidence with heavy ions at +20° and +40° were estimated to be of the order of 1. The prompt emission of light appears to be the principal mechanism which limits complete fusion. A second component of α-particles observed in coincidence with deep-inelastic projectile-like fragments and having an energy comparable to Coulomb energies of particles emitted from target-like and projectile-like fragments appears as an excess yield in the direction of the recoiling target-like fragments. This component cannot be accounted for in terms of sequential emission processes and may result from a mechanism other than the one which leads to fast particle emission.

Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1−9 produced in the reactions of 12 C on 12 C. A total reaction cross section 1170 −100 +170 mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L crit for fusion of 10ħ in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.