Microscopic description of production cross sections including deexcitation effects

Abstract

Background: At the forefront of the nuclear science, production of new neutron-rich isotopes is continuously pursued at accelerator laboratories all over the world. To explore the currently-unknown territories in the nuclear chart far away from the stability, reliable theoretical predictions are inevitable.Purpose: To provide a reliable prediction of production cross sections taking into account secondary deexcitation processes, both particle evaporation and fission, a new method called TDHF+GEMINI is proposed, which combines the microscopic time-dependent Hartree-Fock (TDHF) theory with a sophisticated statistical compoundnucleus deexcitation model, GEMINI++.Methods: Low-energy heavy ion reactions are described based on three-dimensional Skyrme-TDHF calculations. Using particle-number projection method, production probabilities, total angular momenta, and excitation energies of primary reaction products are extracted from the TDHF wavefunction after collision. Production cross sections for secondary reaction products are evaluated employing GEMINI++. Results are compared with available experimental data and widely-used GRAZING calculations. Results:The method is applied to describe cross sections for multinucleon transfer processes in MeV) reactions at energies close to the Coulomb barrier. It is shown that the inclusion of secondary deexcitation processes, which are dominated by neutron evaporation in the present systems, substantially improves agreement with the experimental data. The magnitude of the evaporation effects is very similar to the one observed in GRAZING calculations. TDHF+GEMINI provides better description of the absolute value of the cross sections for channels involving transfer of more than one protons, compared to the GRAZING results. However, there remain discrepancies between the measurements and the calculated cross sections, indicating a limit of the theoretical framework that works with a single mean-field potential. Possible causes of the discrepancies are discussed. Conclusions:In order to perfectly reproduce experimental cross sections for multinucleon transfer processes, one should go beyond the standard self-consistent mean-field description. Nevertheless, the proposed method will provide valuable information to optimize production mechanisms of new neutron-rich nuclei through its microscopic, non-empirical predictions.

Quasifission Dynamics in Microscopic Theories

“…A number of theoretical approaches have been developed that describe the quasifission in terms of multi-nucleon transfer (MNT) processes [41,42,43,44,45,46,47]. Recently, time-dependent Hartree-Fock (TDHF) theory have proven to be an excellent tool for studying QF dynamics, and in particular mass-angle distributions and final fragment total kinetic energies (TKE) [48,31,37,49,32,50,51,52,34,53,45,54,55,56]. While the fragments produced in TDHF studies are the excited primary fragments [57] a number of extensions based on the use of Langevin dynamics have been successfully applied to de-excite these fragments [55,58,59,56,60] Theoretical studies of quasifission dynamics have taught us that dynamics themselves may be dominated by shell effects [61,47].…”

Microscopic studies of production cross sections in multinucleon transfer reaction Ni58+Sn124

“…[42,43,51]. This force has been widely used in the fully three-dimensional TDHF calculations in heavy-ion collisions [34][35][36]42,43,[49][50][51]56,57,[59][60][61].…”

“…The cross sections for secondary products can be used for a direct comparison with the experimental measurement. In present calculation, we employ the default parameter setting in GEMINI++ code, as did in most calculations [60,61,63]. We have also tested the dependence of decay probability on the Monte-Carlo simulation times M event , and found that the decay probabilities are nearly identical for M event =1000 and 10000.…”

“…A simple but effective way is to evaluate the average values of these quantities as shown in Ref. [61]. The average excitation energy and angular momentum of the primary products can be directly obtained from TDHF calculations.…”

“…Quantum effects such as the Pauli principle and antisymmetrization of wave functions are also automatically taken into account in TDHF, which are essential for the manifestation of shell structures during the collision dynamics. TDHF approach has many successful applications in the description of nuclear large amplitude collective motions, as seen in recent applications to fusion [36][37][38][39][40][41][42][43], quasifission [44][45][46][47][48][49][50][51][52], transfer reactions [49,[53][54][55][56][57][58][59][60][61][62][63], fission [64][65][66][67][68], and deep inelastic collisions [69][70][71][72][73][74][75][76][77][78]. However, since the dynamical fluctuation and two-body dissipation are not included in TDHF, the fluctuations of collective variables are found to be considerably underestimated [79,…”