The microscopic description of nuclear fission still remains a topic of intense basic research. Understanding nuclear fission, apart from a theoretical point of view, is of practical importance for energy production and the transmutation of nuclear waste. In nuclear astrophysics, fission sets the upper limit to the nucleosynthesis of heavy elements via the r-process. In this work we initiated a systematic study of intermediate energy proton-induced fission using the Constrained Molecular Dynamics (CoMD) code. The CoMD code implements an effective interaction with a nuclear matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. Moreover, a constraint is imposed in the phase-space occupation for each nucleon restoring the Pauli principle at each time step of the collision. A proper choice of the surface parameter of the effective interaction has been made to describe fission. In this work, we present results of fission calculations for proton-induced reactions on : a) 232 Th at 27 and 63 MeV, b) 235 U at 10, 30, 60 and 100 MeV, and c) 238 U at 100 and 660 MeV. The calculated observables include fission-fragment mass distributions, total fission energies, neutron multiplicities and fission times. These observables are compared to available experimental data. We show that the microscopic CoMD code is able to describe the complicated many-body dynamics of the fission process at intermediate and high energy and give a reasonable estimate of the fission time scale. Sensitivity of the results to the density dependence of the nucleon symmetry potential (and, thus, the nuclear symmetry energy) is found. Further improvements of the code are necessary to achieve a satisfactory description of low energy fission in which shell effects play a dominant role.Understanding the mechanism of nuclear fission, that is the transformation of a single heavy nucleus into two receeding fragments, has been a long journey of fruitful research and debate and, still today, is far from being complete. Upon its discovery, fission was interpreted by Meitner and Frisch [22] as the division of a charged liquid drop due to the interplay of the repulsive Coulomb force between the protons and the surface tension due to the attractive nucleon-nucleon interaction. In the seminal paper of Bohr and Wheeler [23], fission was described with a liquid-drop model and the first estimates of fission probalilities were obtained based on statistical arguments. The first detailed calculations of potential energies of deformed nuclear drops were performed by Frankel and Metropolis in 1947 [24] employing the ENIAC, one of the first digital computers. Despite the success in the interpretation of fission based on the liquid-drop model, the prevailing asymmetry in the mass distribution of the minor actinides could not be deciphered until shell corrections to the macroscopic liquid drop were taken into account (see below). A detailed statistical model that could describe asymmetric fission was...

We investigate the possibilities of producing neutron-rich nuclides in projectile fission of heavy beams in the energy range of 20 MeV/nucleon expected from low-energy facilities. We report our efforts to theoretically describe the reaction mechanism of projectile fission following a multinucleon transfer collision at this energy range. Our calculations are mainly based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The deexcitation/fission of the hot heavy projectile fragments is performed with the Statistical Multifragmentation Model (SMM). We compared our model calculations with our previous experimental projectile-fission data of 238 U (20 MeV/nucleon)+ 208 Pb and 197 Au (20 MeV/nucleon)+ 197 Au and found an overall reasonable agreement. Our study suggests that projectile fission following peripheral heavy-ion collisions at this energy range offers an effective route to access very neutron-rich rare isotopes toward and beyond the astrophysical r-process path.

The investigation of the mechanism of nuclear fission is a topic of current experimental and theoretical interest. In this work, we initiated a systematic study of low and intermediate energy fission calculations using the Constrained Molecular Dynamics (CoMD) code. The code implements an effective interaction with a soft isoscalar part and with several forms of the density dependence of the nucleon symmetry potential. In addition, CoMD imposes a constraint in the phase space occupation for each nucleon restoring the Pauli principle at each time step of the evolution of the nuclear system. In this work, we present results for the reactions p (27 MeV) + 232Th and p (63 MeV) + 232Th and compare them with recent experimental data. It appears that the CoMD code is able to describe the complicated many-body dynamics of the fission process especially for the higher-energy fission reaction. Proper adjustment of the parameters of the effective interaction and further improvements of the code are necessary to achieve a satisfactory quantitative description of low-energy fission where shell effects play a definitive role.

The investigation of the mechanism of nuclear fission is a topic of current experimental and theoretical interest. In this work, we initiated a systematic study of low and intermediate energy fission calculations using the Constrained Molecular Dynami cs (CoMD) code. The code implements an effective interaction with a soft isoscalar part and with several forms of the density dependence of the nucleon symmetry potential. In addition, CoMD imposes a constraint in the phase space occupation for each nucleon restoring the Pauli principle at each time step of the evolution of the nuclear system. Proper choice of the surface parameter of the effective interaction has been made to describe fission. In this work, we present CoMD calculations for several proton- included fission reactions at low and intermediate energy and compare them with recent experimental data. We found that the CoMD code is able to describe the complicated many-body dynamics of the fission process especially for intermediate and higher-energy fission reactions. Proper adjustment of the parameters of the effective interaction and further improvements of the code are necessary to achieve a satisfactory quantitative description of low-energy fission where shell effects play a definitive role.