Classical simulations of heavy-ion fusion reactions and weakly-bound projectile breakup reactions

Heavy-ion collision simulations in various classical models are discussed. Heavy-ion reactions with spherical and deformed nuclei are simulated in a classical rigid-body dynamics (CRBD) model which takes into account the reorientation of the deformed projectile. It is found that the barrier parameters not only on the initial orientations of the deformed nucleus, but also on the collision energy and the moment of inertia of the deformed nucleus. Maximum reorientation effect occurs at near- and below-barrier energies for light deformed nuclei. Calculated fusion cross-sections for ²⁴Mg + ²⁰⁸Pb reaction are compared with a static-barrier-penetration model (SBPM) calculation to see the effect of reorientation. Heavy-ion reactions are also simulated in a 3-stage classical molecular dynamics (3S-CMD) model in which the rigid-body constraints are relaxed when the two nuclei are close to the barrier thus, taking into account all the rotational and vibrational degrees of freedom in the same calculation. This model is extended to simulate heavy-ion reactions such as⁶Li + ²⁰⁹Bi involving the weakly-bound projectile considered as a weakly-bound cluster of deuteron and ⁴He nuclei, thus, simulating a 3-body system in 3S-CMD model. All the essential features of breakup reactions, such as complete fusion, incomplete fusion, no-capture breakup and scattering are demonstrated.     

Timescale for isospin equilibration in projectile breakup

We discuss neutron matter calculations based on chiral effective field theory interactions and their predictions for the symmetry energy, the neutron skin of ²⁰⁸Pb , and for the radius of neutron stars.     

Inclusive and exclusive measurements in the projectile breakup of 7Li

The inclusive and exclusive measurements were carried out for ⁷Li projectile breakup on ²⁷Al target at 48 MeV. In the inclusive data we have observed a broad peak around the beam velocity for alphas and tritons. The exclusive data for alpha-triton coincidences show good agreement with the post-form DWBA theory of breakup reactions.     

A complete low-energy polarized proton-deuteron breakup experiment

An experiment at low energy will be done at the COSY cooler synchrotron and storage ring in order to study the three-particle final states of proton-deuteron scattering reactions measuring a complete set of single and double spin observables over large areas of phase space. The physics objective is to test the predictive power of chiral effective field theory at an energy where convergence is guaranteed and few previous measurements exist. A direct comparison between theoretical predictions and experimental data will be enabled by the use of the so called sampling method.     

A view on reactions of complete fusion

Complete fusion reactions are analysed within the framework of a theoretical model. Energy density interaction potentials are made use of and are renormalized for the purpose. A large number of heavy ion reactions are studied and the calculated critical angular momenta are compared with experimental data.     

Charged pion production and projectile breakup cIN 85A MeV 12C-induced heavy-ion reactions

Charged pions have been measured at 70° in coincidence with projectile-like fragments in ¹²C + ¹²C, ¹²C + ¹¹⁶Sn and ¹²C + ¹²⁴Sn reactions at 85A MeV. Neither the π⁺ emission nor the π⁻/π⁺ ratio exhibit differences for ¹²⁴Sn and ¹¹⁶Sn targets outside those expected from the isospin difference. Inconsistencies in the target mass dependence of the pion yield disappear if a correction for reabsorption is included. After this correction, we observe a strong, ~ A^1.1, mass dependence. The projectile breakup is significantly stronger for pion-producing collisions than for the average collision indicating a much stronger abundance of central collisions.     

Relating breakup and incomplete fusion of weakly bound nuclei through a classical trajectory model with stochastic breakup

A classical dynamical model that treats breakup stochastically is presented for low energy reactions of weakly bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete, and complete fusion cross sections. The model is assessed by comparing the breakup observables with continuum discretized coupled-channel quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.     

A dynamical model for projectile break-up and incomplete fusion

A classical dynamical model is presented for the reaction ²⁰Ne on ¹⁹⁷Au. ²⁰Ne is considered as a bound system of five alpha particles which individually interact with the target via a folding potential and frictional forces. Results for complete fusion, differential cross sections for the various possible ejectiles and coincidence cross sections are presented and compared to experiment.     

Influence of projectile cluster properties on fragment emission in incomplete-fusion reactions

The influence of projectile cluster properties on the fragment emission in incomplete-fusion reactions is studied. In the framework of a direct-transfer model analytic expressions concerning the parallel width and he maximum of the fragment yield are derived within some approximations. The expressions exhibit a strong dependence upon the cluster properties of the projectile, viz. the binding energy of the fragments and the characteristic fragment sizes associated with the projectile cluster state. The comparison with experimental data confirms the predicted dependence.     

Dinuclear systems in complete fusion reactions

Formation and evolution of dinuclear systems in reactions of complete fusion are considered. Based on the dinuclear system concept, the process of compound nucleus formation is studied. Arguments confirming the validity of this concept are given. The main problems of describing the complete fusion in adiabatic approximation are listed. Calculations of evaporation residue cross sections in complete fusion reactions leading to formation of superheavy nuclei are shown. Isotopic trends of the cross sections of heavy nuclei formation in complete fusion reactions are considered.     

Double ionization of helium by electron-impact: complete pictures of the four-body breakup dynamics

The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)].     

Nuclear matter incompressibility effect on the cross-section of fusion reactions with a weakly bound projectile

Fusion reactions with a weakly bound projectile are studied using the double-folding model along with a repulsive interaction modifying term.Using this modified potential,including nuclear matter incompressibility effects,the fusion reaction cross sections and suppression parameters are calculated for9Be+209Bi,208Pb,29Si and27Al reactions.The results show that applying these effects at energies near the Coulomb barrier improves the agreement between the calculated and experimental cross sections,and modifies the mean values of the suppression parameter.     

Decay of the complete fusion nucleus,151Eu

Excitation functions have been measured for the¹³³Cs(¹³O, 3–6n)^145–148Eu reactions at incident energies from 75 to 125 MeV and compared to those previously reported for the¹³⁹La(¹²C, 3–6n) reaction system with the same complete fusion nucleus,¹⁵¹Eu. The semiclassical Diamond-Stephens approach to the treatment of angular momentum in evaporative processes is extended and a method for extraction of the moment of inertia, the critical value of angular momentum for fusion, and the yrast line for¹⁵¹Eu is presented. The model is then used to predict the excitation functions and the results are compared to experiment.     

Near-barrier fusion, breakup and scattering for the Be + Sm system

Fusion, breakup and scattering for the ⁹Be + ¹⁴⁴Sm system at near barrier energies are investigated by different approaches. We show that at energies above the barrier there is a small complete fusion suppression when compared with predictions from a double folding potential and with a similar tightly bound system. At sub-barrier energies there is no significant deviation from the predictions using coupled channel calculations that do not include the breakup channel. The energy dependence of the optical potential does not show the usual threshold anomaly found in tightly bound systems. From a simultaneous analysis of fusion and scattering data we estimate the distance where breakup starts to occur.