Cascade model of inelastic interactions of α-particles with nuclei

Based on the two-component model (direct plus thermal) introduced in a previous article we calculate and discuss proton-inclusive energy and angular distributions associated with low- and high-multiplicity selected events. In particular, we study proton production from Ne on U and Ne on Al at 400 MeV/N, and from Ar on KCl at 800 MeV/N.     

Non-equilibrium processes in heavy-ion collisions at relativistic energies

We use transport theory to describe the inclusive cross sections for protons and pions produced in collisions between two identical heavy ions at an energy of 800 MeV per particle. In addition to the nucleonic we take the Δ-degree of freedom into account. Thus we consider a two-component system whose distributions in transverse momentum and rapidity we describe by two coupled Fokker-Planck equations. These transport equations contain the one-nucleon knock-out process as initial condition. In the limit of large interaction times they lead to thermal equilibrium (fireball) distributions. For light nuclei the interaction time is not large enough for equilibrium to be reached. A recent experiment for two colliding carbon nuclei at 800 MeV per nucleon shows evidence of nonequilibrium effects. We compare our calculations with experimental data for ¹²C on ¹²C and Ne on NaF at 800 MeV/N.     

Non-equilibrium dynamics in high-energy nucleus-nucleus collisions: (II). Calculation of inclusive particle spectra

We present theoretical results for proton, deuteron, triton, ³He and ⁴He inclusive particle spectra measured in 250 MeV/amu and 400 MeV/amu nucleus-nucleus reactions. The calculations are based on a multiple collision model which is derived from the relativistic Boltzmann equation and which includes composites formation through thermodynamics. The agreement with the data is reasonable to good and the remaining discrepancies are discussed.     

Effects of density-and momentum-dependent potentials in Au+Au collisions at intermediate energies

Based on an isospin-dependent transport model, the effects of the density-and momentum-dependent potentials are studied by simulating Au on Au collisions at 90, 120, 150 and 400 MeV/nucleon. It is found that the calculated results overestimate the experimental data on the directed flow and underestimate the data on the elliptic flow for protons. The impact of the density-and momentum-dependent potentials is observed in the mid-rapidity region of the final spectra. At 90 MeV/nucleon, the momentum-dependent potential has a larger impact on the observables than the density-dependent potential, and the elliptic flow has a higher value with the positive effective mass splitting. At 400 MeV/nucleon, however, the opposite is observed. The rapidity dependence of the elliptic flow for protons is sensitive to the symmetry energy. A soft symmetry energy corresponds to a higher value of the proton elliptic flow.     

Deuteron formation in nuclear collisions

Deuteron production cross sections are calculated from an intranuclear cascade model for Ne + U and Ar + Ca at 400 MeV/A. In effect, there are no adjustable parameters in this calculation. The parameters of the cascade code are fixed by sum charged inclusive data. Furthermore, the high momentum deuteron inclusive distribution is found to be insensitive to the details of the deuteron wave function. This latter observation leads to a justification of a generalized coalescence formula involving both momentum and spatial coordinates. Satisfactory agreement is found between our calculations and both the untriggered and high multiplicity triggered inclusive spectra of deuterons with energies ?50 MeV/A.     

Prompt light particle emission in the 36Ar + 58Ni reaction at 95 MeV/nucleon

The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function of impact parameter. The results are compared with experimental data from the ³⁶Ar + ⁵⁸Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity. Received: 27 July 2000 / Accepted: 20 November 2000     

Kinetic energy flow analysis of high-energy heavy-ion collisions: The classical equation of motion approach

The results of a kinetic energy flow analysis carried out on the basis of the classical equation of motion model are presented for the reactions Ne + U, Ca + Ca and Nb + Nb at 400 MeV/nucleon. The model satisfactorily reproduces the global values of the events and the side-splash effect observed in the experiment. The flow angle turned out to be sensitive to the effective NN potential model which parametrizes the compression dynamics.     

A quark signature in the nuclear fireball model of heavy ion collisions

It seems possible that a definite quark matter signature may be observed in the near future in nuclear heavy ion collisions. For example, in experiments yielding a fireball temperature of at least 180 MeV, a lab energy of ～ 11 GeV/nucleon must be reached for a ²⁰Ne + U collision. These energies should be sufficient to produce quark matter in the fireball. The signature of this transition is observed by comparing particle spectra at higher energies. It is expected that once quark matter is reached the spectrum will remain constant at temperature greater than ～ 180 MeV, rather than continue to change with energy.     

Fragment kinetic energies and modes of fragment formation

Kinetic energies of light fragments ( A相似文献   

New direct reaction: two-proton knockout from neutron-rich nuclei

The reaction 9Be(28Mg,26Ne+gamma)X has been studied at 82 MeV/nucleon together with two similar cases, 30Mg and 34Si. Strong evidence that the reactions are direct is offered by the parallel-momentum distributions of the reaction residues and by the inclusive cross sections. The pattern of the partial cross sections for 28Mg suggests the presence of correlations. A preliminary theoretical discussion based on eikonal reaction theory and the many-body shell model is presented. The reaction holds great promise for the study of neutron-rich nuclei.     

Peripheral reactions induced by 20Ne at 11 and 15 MeV/nucleon

The breakup of ²⁰Ne has been studied in the ²⁰Ne + ⁵⁴Fe reaction at 11 and 15 MeV/nucleon. Singles projectile-like fragments and correlations between projectile-like fragments and α-particles have been measured. The correlations have been analysed in terms of sequential breakup by extensive Monte Carlo simulations. The major part of the data, even at high-excitation energy, can be described by sequential decay. The large contribution of sequential decay to the inclusive yield is confirmed. Strong energy dissipation is observed, which cannot be accounted for by direct transfer or nucleon exchange.     

Exclusive measurements of light fragment production at forward angles in Ne-Pb and Ne-NaF collisions at E/A=400 MeV and 800 MeV

Emission of light fragments at small angles is studied in relativistic heavy ion collisions using the Diogene plastic wall for both symmetrical and non-symmetrical target-projectile systems with 400 MeV per nucleon and 800 MeV per nucleon incident neon nuclei. Efficiency of multiplicity measurements in the small angle range for the selection of central or peripheral collisions is confirmed for asymmetric systems. Differential production cross sections of Z = 1 fragments show evidence for the existence of two emitting sources. The apparent temperature of each source is obtained from comparison with a thermodynamical model.     

Quasi-elastic nucleon transfer and single charge exchange in 48Ti + 42Ca collisions

Single nucleon transfer and single charge exchange have been studied for quasi-elastic collisions of ⁴⁸Ti and ⁴²Ca at E_lab = 240, 300 and 385 MeV. Specific features below 12 MeV excitation energy are displayed in all of the measured particle energy spectra for each channel. These have been accounted for in the case of nucleon transfer by a one-step direct transfer mechanism in which all of the available hole and bound particle states in the donor and acceptor nucleus, respectively, have been included. This core excitation model was extended to single charge exchange (SCX) two-step transfers in which a proton and a neutron are exchanged. The absolute magnitude and distribution of strength in the SCX channel was obtained. The contributions from direct charge exchange via the isovector parts of the NN interaction has also been investigated in a microscopic model and is found to contribute of the order of 1–5% to the charge exchange cross section. The distribution of Fermi and Gamow-Teller strength is discussed.     

Proton production in nucleus-nucleus collisions at 400 MeV/nucleon: A possible explanation for the anisotropy in the inclusive spectra

We investigate proton inclusive production in nucleus-nucleus collisions at 400 MeV/ nucleon within the framework of a multiple collision approach based on sequences of independent baryon-baryon collisions. We take explicitly into account the beam energy dependence of the inverse slope of the elementary NN differential scattering cross section which turns out to be essential for a reasonable agreement with the data concerning the 30 to 90 degree ratio of the c.m. spectrum.     

Particle Production in Non-equilibrium Thermodynamic States in Nucleus-Nucleus Collisions

The formation of nonequilibrium thermodynamic system is assumed during the collision of relativistic heavy ions with target nuclei. A simple classical solution of the Boltzmann equation is found and compared with the spectra of particles produced in the Ne-U²³⁸ reaction at lab. energies of 250 and 400 MeV per nucleon. The model contains only one fitting parameter t_c which is the time required by the system to reach the equilibrium state.     

The production of high-energy protons in central relativistic nuclear collisions

We extend our model of transport theory to be applicable to the inclusive production of protons with very high energy. We then consider the angular distribution of such protons, produced in a central collision of Ar on KC1 at 800 MeV per nucleon. The slight anisotropy observed in the data can be explained by a finite value of the friction constant which in turn determines the number of collisions needed for equilibrium to be reached. We also show that these data are quite sensitive to the reaction geometry and cannot be explained by the firestreak model.     

Measurement of the 2H(p,n) Breakup Reaction at 170 MeV and the Three-Nucleon Force Effects

The effects of three nucleon force (3NF) have been actively studied via the nucleon–deuteron (Nd) scattering states. The differential cross sections and the vector analyzing powers A _y of the ²H(p, n) inclusive breakup reaction at 170 MeV were measured for the study of 3NF effects in the intermediate energy region. The polarized proton beam of 170 MeV was injected to the deuterated polyethylene (CD₂) target and the energy of scattered neutrons were measured by using TOF method. The data were compared with the Faddeev calculations based on modern nucleon–nucleon (NN) forces with and without the 3NF. Concerning the differential cross sections, we can see large discrepancies between the data and the calculations in the region of scattered neutron energies are low, which is similar to the results of the ²H(p, p) inclusive breakup reaction at 250 MeV.     

HEAVY ION COLLISIONS AND QUARK DISTRIBUTION IN NUCLEI

The heavy-ion collisions are studied by means of two-component Fokker-Planck equations on the assumption that there exist multiquark states in nuclei. Inclusive cross section for the production of p is calculated in heavy-ion collisions of C+C, Ne+NaF and Ar+KCI at 800 MeV/N; Ne+NaF at 400 MeV/N, 800 MeV/N and 2100 MeV/N. A satisfactory agreement with the experimental data near c.m. 90 degree is obtained. The production of d in the collision of C+C at 800 MeV/N is also discussed.