V. V. Samarin

Description of nucleon-transfer and fusion reactions within time-dependent approaches and coupled-channel method

The time-dependent Schrödinger equation and the method of perturbed stationary states that is based on the expansion of the total wave function for the system of two nuclear cores and a nucleon in a set of nucleon two-center functions are used to describe nucleon transfers and fusion in low-energy nuclear reactions. A set of multichannel equations that couple the relative motion of nuclei to the motion of the nucleon is obtained. The kinetic-energy coupling matrix is similar to the coupling matrix for collective excitations of nuclei.

Quantum description of coupling to neutron-rearrangement channels in fusion reactions near the Coulomb barrier

The fusion cross sections for the 17,18O+27Al, 18O+58Ni, and 6He+197Au reactions were calculated by the coupled-channel method. The radial dependence of matrices that describe coupling to valence-neutron-rearrangement channels was determined with the aid of two-center wave functions. The coupling-strength parameters were evaluated on the basis of numerically solving the time-dependent Schrödinger equation. Satisfactory agreement with experimental data was obtained.

Role of neutrons in the fusion of nuclei

The problem of a quantum-mechanical description of a near-barrier fusion of heavy nuclei under conditions of a strong coupling of their relative motion to neutron degrees of freedom is studied. New mutually complementing efficient models employing the multidimensional time-dependent Schrödinger equation and methods for numerically solving the problems in question within these models are proposed. This makes it possible to study the evolution of wave functions for outer neutrons and to calculate nucleontransfer probabilities and occupation numbers for quasimolecular states over the entire energy range, including that of deep-subbarrier energies. It is shown that the valence-neutron wave functions extend over the volumes of both colliding nuclei before their surfaces come into contact and even before these nuclei overcome the Coulomb barrier (collectivization of outer nucleons). This gives rise to a substantial neutron-transfer effect on the fusion of nuclei and, in particular, to a sizable increase in the probability of subbarrier fusion for specific combinations of nuclei.

Study of ground states of 3 H, 3,4,6 He, 6 Li, and 9 Be nuclei by Feynman’s continual integrals method

The ground-state energies and the squared moduli of the ground-state wave functions are calculated for the 3H, 3,4,6He, 6Li, and 9Be nuclei by Feynman’s continual (path) integrals method. The results are in satisfactory agreement with experimental data.

Peculiarities in total cross sections of reactions with weakly bound nuclei 6 He, 9 Li

The energy dependence of the total cross sections for the 6He + Si and 9Li + Si reactions was measured at beam energies between 5 and 20 MeV per nucleon. The results agree with experimental data published for the 6He + Si reaction. New data are obtained for the 9Li + Si reaction in the vicinity of a local enhancement of the total cross section. A theoretical analysis of the possible reasons behind the appearance of this peculiarity in the case of collisions of 6He and 9Li nuclei with silicon target nuclei is performed. In particular, the enhancement may owe its origin to the effect of loosely bound projectile nucleons.

Time-Dependent Description of Incomplete Fusion of Nuclei and Cluster and Nucleon-Transfer Reactions

A numerical solution of the time-dependent Schrödinger equation is applied in studying the dynamics of incomplete fusion of nuclei and cluster- and nucleon-transfer reactions at energies near the Coulomb barrier. The evolution of wave functions for all nucleons is used to describe multineutron- and multiproton-transfer reactions in 40Ca+124Sn collisions. The results of the calculations are in satisfactory agreement with experimental data. The evolution of the alpha-cluster wave function in the 12C nucleus is used to calculate the incomplete-fusion cross section for the 12C+51V reaction. Agreement with experimental data for the (12C, α) and (12C, 2α) channels is attained.

Energy Dependence of Total Cross Sections for Reactions with 4, 6he, 6, 7, 9li Nuclei

The paper presents the results of measurement of the total cross sections for reactions 4,6He + Si and 6,7,9Li + Si in the beam energy range 5−50 A⋅MeV. The enhancements of the total cross sections for reaction 6He + Si compared with reaction 4He + Si, and 9Li + Si compared with reactions 6,7Li + Si have been observed. The performed microscopic analysis of total cross sections for reactions 6He + Si and 9Li + Si based on numerical solution of the time-dependent Schrodinger equation for external neutrons of projectile nuclei 6He and 9Li yielded good agreement with experimental data.

Role of external neutrons of weakly bound nuclei in reactions with their participation

The paper presents the results of measurement of the total cross sections for reactions 4,6He+Si and 6,7,9Li+Si in the beam energy range 5–50 A MeV. The enhancements of the total cross sections for reaction 6He+Si compared with reaction 4He+Si and 9Li+Si compared with reactions 6,7Li+Si have been observed. The performed microscopic analysis of total cross sections for reactions 6He+Si and 9Li+Si based on numerical solution of the time-dependent Schrodinger equation for external neutrons of projectile nuclei 6He and 9Li yielded good agreement with experimental data.

Near-Barrier Proton Transfer in Reactions with 3 He Nucleus

Calculations of production cross sections for isotopes 194Au in the 3He + 194Pt reaction and 45Ti in the 3He + 45Sc reaction are performed, based on the solution to a time-dependent Schrödinger equation in combination with calculations in the statistical model using the computational code of the NRV data base. The experimental differences in the near-barrier energy dependences of the isotope production cross sections in these reactions are explained by the difference between the proton and neutron shells of the target nuclei, and by the different evolutions of the probability density for protons of the projectile nucleus and neutrons of the target nuclei in collisions.

Near-barrier neutron transfer in reactions 3,6He + 45Sc and 3,6He + 197Au

Experimental cross sections for formation of 196,198Au isotopes in reactions 3,6He + 197Au and cross sections for formation of 44,46Sc isotopes in reactions 3,6He + 45Sc have been analyzed. To calculate neutron transfer probabilities and cross sections the time- dependent Schrodinger equation for external neutrons of 3He, 6He, 45Sc and 197Au nuclei has been solved numerically. It is shown that the contribution of fusion and subsequent evaporation is significant in the case of reactions 3,6He + 45Sc, whereas in the case of reactions 3,6He + 197Au, it is negligible. Fusion-evaporation was taken into account using NRV evaporation code. Results of calculations demonstrate overall satisfactory agreement with experimental data.