Transfer and fusion reactions of unstable nuclei

The transfer and fusion reactions are studied for reactions between a stable and an unstable nucleus with neutron skin, taking as examples the reactions ^16,28O+⁴⁰Ca. The two-dimensional time-dependent Hartree-Fock method is used. It is shown that, in such reactions, the nucleon transfer is enhanced enormously for both protons and neutrons. The neutron skin does not enhance the fusion cross section contrary to the usual expectation.     

Multi-nucleon transfer reactions and fusion with unstable nuclei

We show that a large number of neutrons are expected to be transferred from the projectile to the target if a neutron rich unstable nucleus with a neutron skin is used as the projectile in heavy-ion collisions at energies about twice the Coulomb barrier. We then show that though the neutron halo enhances the fusion cross section through the size effect, the additional effect due to the molecular bond formation is not significant in the fusion between ¹¹Li and ⁹Li at energies near and below the Coulomb barrier.     

Production of super-heavy nuclei in cold fusion reactions

A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a ²⁰⁸Pb target nucleus is discussed.In the framework of this model,the production of the com-pound nucleus by two paths,the di-nuclear system path and the fusion path,are taken into account simultaneously.The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucle-ons from the light nucleus to the heavy one.The fusion path is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus.It is shown that the compound nucleus is mainly formed by the fusion path in cold-fusion reactions.The landscape of the potential energy related to the fusion path is discussed in detail.This landscape for very heavy nucleus-nucleus systems has an intermediate state,which is linked to the formation of both the compound nucleus and the quasi-fission fragments.The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections.The values of the cold-fusion cross sections obtained in the model agree well with the experimental data.     

Statistical properties of fusion reactions involving deformed nuclei

The statistical properties of the ¹⁶⁵Ho(α,2nγ) ¹⁶⁷Tm reaction were investigated. It was found that both the slopes of the excitation functions and the side-feeding intensities are independent of the K quantum number. Regular behaviour of these quantities as a function of the spin I and of the excitation energies of the observed levels provide a means for spin assignments, just as for spherical nuclei. The analysis, in the present case, however, is much more involved.     

Cross sections of fusion and transfer reactions in interactions between 3He and Pt and 197Au nuclei in the subbarrier energy region

The reactions of complete and incomplete fusion, along with nucleon transfer reactions in the range of ³He energies from 10 to 24.5 MeV, are investigated by irradiating gold and platinum targets with an accelerated ³He ion beam on the U-120M cyclotron at the Institute of Nuclear Physics, Czech Academy of Sciences, ?e?. Activation is used to determine the yield of nuclides resulting from nuclear reactions. The γ-activity induced in the targets is measured using a with high-resolution HPGe detector. Despite the low binding energy of ³He and the reactions with positive Q values, the measured cross sections of fusion reactions exhibit no specific features, compared to reactions conducted using beams of other light stable particles. Transfer neutron reactions in the subbarrier energy region have relatively high cross sections. These cross sections continue to grow as the energy of ³He rises. When a neutron is captured by a nucleus of ³He, the cross sections of these reactions reach their maximum values in the Coulomb barrier region.     

Production mechanism of superheavy nuclei in massive fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus and the de-excitation process are calculated by using an empirical coupled channel model, solving a set of microscopically derived master equations numerically and applying statistical theory, respectively. Fusion-fission reactions and evaporation residue excitation functions of synthesizing superheavy nuclei (SHN) are investigated systematically and compared them with available experimental data. The possible factors that affecting the production cross sections of SHN are discussed in this workshop.     

Production mechanism of superheavy nuclei in massive fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus and the de-excitation process are calculated by using an empirical coupled channel model, solving a set of microscopically derived master equations numerically and applying statistical theory, respectively. Fusion-fission reactions and evaporation residue excitation functions of synthesizing superheavy nuclei (SHN) are investigated systematically and compared them with available experimental data. The possible factors that affecting the production cross sections of SHN are discussed in this workshop.     

The dynamics of the fusion of two nuclei

The prediction of the need for an extra push over the interaction barrier in order to make the heavier nuclei fuse is made the basis of a simple algebraic theory for the energy dependence of the fusion cross section. The predictions are compared with recent experiments. A graphical construction, designed to extract directly the three parameters of the theory, suggests about 33 for the effective fissility (Z²/A)_eff [defined as $\text{4Z}{}_1\text{Z}{}_2\text{/A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}{}_1\text{A}{}^{\mathrm{<mtext>case1</mtext><mtext>3</mtext>}}{}_2\text{(A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}{}_1\text{+ A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}{}_2$)] beyond which an extra push is needed, determines the initial rate of increase of the square root of the extra push (in MeV) as about one per unit excess of (Z²/A)_eff over 33 and indicates an effective centrifugal repulsion opposing fusion (in cases when angular momentum is present) not very different from that expected for two spheres rolling on each other without sliding.     

Rotational to vibrational evolution in some rotational-like nuclei

The excitation spectra of nuclei in the regions 150156Gd. Also we have shown the result of the nucleus ¹⁰²Ru which is given as an example of the reverse transition, i.e., vibration to rotation. The TRS plots reveal that, as the spin increases up the band, the former nucleus becomes slightly soft in γ and β direction, whereas the latter becomes rigid in γ direction.     

High energy collisions between heavy nuclei

Neglecting Coulomb effects we derive a very simple analytical result for nucleus-nucleus elastic scattering in an optical limit of the Glauber approximation which has the property that it does not diverge at large momentum transfers when the center-of-mass correlation function is retained and is more accurate and easier to apply than the commonly used expressions which involve numerical integrations. We then derive a corresponding analytical expression for the elastic scattering amplitude which includes the Coulomb effects arising from point charge incident and target nuclei.     

Pulsed ion hall accelerator for investigation of reactions between light nuclei in the astrophysical energy range

The factors defining the constraints on the current characteristics of the magnetically insulated ion diode (IDM) are considered. The specific current parameters close to the maximum possible ones are obtained for the particular IDM-40 design assigned for acceleration of light ions and investigation of nuclear reactions with small cross sections in the astrophysical energy range (2–40 keV) in the entrance channel. It is experimentally demonstrated that the chosen optimal operation conditions for IDM-40 units provide high stability of the parameters (energy distribution and composition of accelerated particle beams, degree of neutralization) of the accelerated particle flux, which increases during the working pulse.     

A study of fusion reactions between206, 207Pb nuclei and40Ar ions near the coulomb barrier

Excitation functions for the reactions²⁰⁶Pb(⁴⁰Ar, 2n)²⁴⁴Fm and²⁰⁷Pb(⁴⁰Ar, 3n)²⁴⁴Fm have been measured and analysed in terms of a statistical model. The optical potential parameters have been found to be as follows:V ₀=? 70 MeV,r ₀=1.26×10^?13 cm andd =0.36×10^?13 cm. Some data on the properties of the excited compound nucleus of fermium have been obtained.     

One dimensional three-body model for low energy reactions of halo nuclei

One dimensional three-body model which simulates the low energy reactions of the nuclei with halo structure, is investigated by solving exactly the three-body Schrödinger equation. The dynamical roles of the halo neutron during the reaction are studied in detail. The decrease of the fusion probability, as well as the large transfer and break-up probabilities, are found for halo nuclei.     

Bonding potential between two12C nuclei

The potential between two¹²C nuclei in linear chain configuration has been calculated microscopically using the Ali-Bodmerα-α potential. This potential shows a pocket and compares well in the tail region with the phenomenological potential extracted before, from the data on the quasi-molecular resonances of the¹²C +¹²C system. This provides support to the diatomic like rotation-vibration picture of quasi-molecular states.     

Angular distribution of fission fragments in reactions of complete fusion of deformed nuclei

Formation of angular distributions of fission fragments for the ¹⁶O + ²³²Th and ¹²C + ^235,236U reactions has been analyzed within a dynamic approach. In this approach, the component of the total angular momentum along the fission axis K is considered as a fluctuating quantity and the corresponding relaxation time is assumed to be the main parameter controlling the evolution of this mode. Particular attention is paid to the analysis of the effect of initial distributions over K (formed during fusion) on the angular distribution of fission fragments of nuclei having fission barriers comparable with the nuclear temperatures.     

The excitation functions of complete and incomplete fusion reactions of 6Li with Pt nuclei

Experimental results from measuring the energy dependences of cross sections of fusion and transfer reactions for ⁶Li beams and Pt targets are presented. The experiments were performed using the MSP-144 magnetic analyzer; stacks of platinum foils were installed at the focal plane of this analyzer. In the energy range 22.5–42.5 MeV, the energy resolution of the beam hitting the target stack was not worse than 0.25 MeV and that of the transmitted beam was not worse than 0.40 MeV. The yields of products of neutron and deuteron transfer reaction on target nuclei were measured using the γ activity induced in the platinum targets. Thus, excitation functions for transfer reactions were obtained in a wide energy range, including near the Coulomb barrier. It was shown that the basic reaction channel is the deuteron capture from ⁶Li. In this case, the maximum of the excitation function for ⁶Li breakup and subsequent deuteron capture lies near the Coulomb barrier of the reaction.     

Probing the nuclear symmetry energy with heavy-ion reactions induced by neutron-rich nuclei

Heavy-ion reactions induced by neutron-rich nuclei provide a unique means to investigate the equation of state of isospin-asymmetric nuclear matter, especially the density dependence of the nuclear symmetry energy. In particular, recent analyses of the isospin diffusion data in heavy-ion reactions have already put a stringent constraint on the nuclear symmetry energy around the nuclear matter saturation density. We review this exciting result and discuss its implications on nuclear effective interactions and the neutron skin thickness of heavy nuclei. In addition, we also review the theoretical progress on probing the high density behaviors of the nuclear symmetry energy in heavy-ion reactions induced by high energy radioactive beams.      

Reactions between complex nuclei. The frontier between complete fusion and other dissipative collisions

In a first part, we discuss the distinction between complete fusion followed by the compound nucleus decay and incomplete fusion due to massive transfers. In the second part, we analyse the origin of fission-like products resulting from the disruption of a long-life intermediate system. Forl-waves corresponding to a rotating liquid drop fission barrier equal to zero, a quasi fusion process occurs which leads finally to characteristics very similar.     

Pathway of membrane fusion with two tension-dependent energy barriers

Fusion of bilayer membranes is studied via dissipative particle dynamics (DPD) simulations. A new set of DPD parameters is introduced which leads to an energy barrier for flips of lipid molecules between adhering membranes. A large number of fusion events is monitored for a vesicle in contact with a planar membrane. Several time scales of the fusion process are found to depend exponentially on the membrane tension. This implies an energy barrier of about 10k(B)T for intermembrane flips and a second size-dependent barrier for the nucleation of a small hemifused membrane patch.