Fission barriers in actinides and its parameter dependence in mean field theory

Spontaneous fission is one of the prominent decay channels of (super) heavy nuclei. The size of fission barrier of a nucleus is a measuring parameter for the fission lifetime of the nucleus. Nowadays various model dependent calculations of fission properties, with their own merits and demerits, are available. Here the self-consistent relativistic mean field (RMF) prediction of fission barrier height and fission isomer energy in even-even actinides is presented. The standard covariant Lagrangian density is solved for two different sets of well known force parameters, namely NL3 and TMA. The Fermion and the Boson field equations are solved in an axially deformed harmonic oscillator basis having frequency ħω = 41A-1/3 and number of shells 20 both for the Fermion and the Boson fields. The pairing interaction is treated as per the standard BCS formalism with gap parameters: Δn(p) = 4.8/N1/3(Z1/3) and an energy dependent pairing window is chosen as εi - λ ≤ 41A-1/4. The energy surface of all the even-even actinide isotopic chains is calculated and extracted the fission barrier height and the energy of the superdeformed fission isomer. As an illustration the inner fission barrier EA (upper panel) is shown and the isomer energy EII (lower panel) for the U and Pu isotopes only. The experimental values (whenever available) and the results of the Skyrme SkM and Gogny D1S functionals are shown. It is observed that the NL3 and TMA forces predict inner fission barriers of even-even actinides that are more or less similar to the nonrelativistic SkM and D1S model, but the relativistic model deviates at the neutron-rich side and produces higher values of EA. Note that the NL3 force with a slightly different consideration of pairing gap also overestimates/underestimates the experimental EA values for the U/Pu isotopes, and triaxiality substantially reduces the barrier heights. The RMF+BCS predictions of EII is also significantly higher than the experiment as well as the SkM and/or D1S prediction. A systematic calculation with various force fields and pairing schemes is under progress