Background: Multinucleon transfer reaction at low-energy collisions is considered to be a promising method for the production of new exotic nuclei, which are difficult to be produced by other methods. The theoretical studies are required to provide reliable predictions for the experiments and promote the understanding of the microscopic mechanism in multinucleon transfer reactions. Purpose: We provide a predictive approach for production cross sections, and testify how and to what extent the microscopic approach works well in multinucleon transfer reaction. Methods: We employ the approach TDHF+GEMINI, which combines the microscopic time-dependent Hartree-Fock (TDHF) with the state-of-art statistical model GEMINI++, to take into account both the multinucleon transfer dynamics and the secondary deexcitation process. The properties of primary products in multinucleon transfer process, such as transfer probabilities and primary cross sections, are extracted from TDHF dynamics by using the particle-number projection method. Production cross sections for secondary products are evaluated by using the statistical model GEMINI++.Results: We investigate the influence of colliding energies and deformation orientations of target and projectile nuclei on multinucleon transfer dynamics in the reaction 58 Ni+ 124 Sn. More nucleons are observed to transfer in the tip collision as compared to the side collision. The production cross sections for secondary fragments with TDHF+GEMINI calculations well reproduce the experimental measurements at energies close to the Coulomb barrier. At sub-barrier energy, the theoretical results gradually deviate from the experimental data as the increase of the number of transferred neutrons, implying the limitations of a single mean-field approximation in TDHF approach. Possible origins for this discrepancy are discussed. The total cross sections integrated over all the neutron pickup channels are in good agreement with the experimental data for all the energies. We compare the production cross sections of TDHF+GEMINI calculations with those from GRAZING model, and find that our approach gives a quantitatively good description as the semiclassical model, although there is no adjustable parameters for the reaction dynamics in the microscopic TDHF method. Conclusions: The microscopic approach TDHF+GEMINI reasonably reproduces the experimental data at energies close to the Coulomb barrier and well accounts for the multinucleon transfer mechanism. The present studies clearly reveal the applicability of TDHF+GEMINI method in multinucleon transfer reactions, which thus deserves as a promising tool to predict the properties of new reactions. * luguo@ucas.ac.cn hance the yield of exotic nuclei for an appropriate projectiletarget combination. To produce the new unstable isotopes experimentally, the optimal incident energy and projectile-target combination should be chosen to have the highest product cross section for the desired isotope. The reliable theoretical predictions are therefore required to guide ...
Background: Quasifission and fusion-fission are primary mechanisms to prevent the production of superheavy elements. The recent experimental measurements reveal that the fusion-evaporation cross section in the 3n reaction channel of 48 Ca+ 239 Pu is 50 times lower than using 244 Pu as target nucleus [Phys. Rev. C 92, 034609 (2015)]. However, the precise mechanisms of this remarkable isotopic dependence are not well understood.Purpose: To understand the experimental observation of the rapid decrease of stability of superheavy nuclei as the neutron number decreases, the theoretical studies of quasifission and fusion-fission in connection with experimental production for Z=114 flerovium isotopes are required to investigate the possible differences in reaction mechanisms induced by these two targets.Methods: We propose an approach called TDHF+HIVAP to take into account both the evolution of dinuclear system and the deexcitation of compound nucleus, which combines the microscopic time-dependent Hartree-Fock (TDHF) method for the fusion and quasifission dynamics with the statistical evaporation model HIVAP for fusion-fission dynamics.Results: Fusion is observed for both reactions 48 Ca+ 239,244 Pu with the side orientation the deformed target nucleus, while quasifission dynamics is observed for the tip orientation. The nuclear contact times, masses and charges as well as the kinetic energies of the fragments, and the massangle distribution strongly depend on the colliding energy, impact parameter, and deformation orientation. The quantum shell effect displays a crucial role in both the quasifission and the fusionfission processes. The quasifission is considerably reduced and the survival probability is enhanced around one order of magnitude in the reaction using 244 Pu target as compared to the 239 Pu case.Conclusions: The studies by using TDHF+HIVAP method well account for the experimental observations and the present method clearly shows its applicability in the reaction mechanisms of quasifission and fusion-fission dynamics. The experimental and theoretical results encourage the use of neutron-rich targets for the production of new superheavy elements.
We examine the effects that dynamical instability has on shaping the orbital properties of exoplanetary systems. Using N-body simulations of non-EMS (Equal Mutual Separation), multi-planet systems we find that the lower limit of the instability timescale t is determined by the minimal mutual separation K min in units of the mutual Hill radius. Planetary systems showing instability generally include planet pairs with period ratio < 1.33. Our final period ratio distribution of all adjacent planet pairs shows dippeak structures near first-order mean motion resonances similar to those observed in the Kepler planetary data. Then we compare the probability density function (PDF) of the de-biased Kepler period ratios with those in our simulations and find a lack of planet pairs with period ratio > 2.1 in the observations-possibly caused either by inward migration before the dissipation of the disk or by planet pairs not forming with period ratios > 2.1 with the same frequency they do with smaller period ratios. By comparing the PDF of the period ratio between simulation and observation, we obtain an upper limit of 0.03 on the scale parameter of the Rayleigh distributed eccentricities when the gas disk dissipated. Finally, our results suggest that a viable definition for a "packed" or "compact" planetary system be one that has at least one planet pair with a period ratio less than 1.33. This criterion would imply that 4% of the Kepler systems (or 6% of the systems with more than two planets) are compact.
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