A study of U-isotope ground state properties with covariant energy density functional

In this study,we systematically analyzed the ground state of uranium isotopes from 225 to 240.In our calculations,we used the covariant energy density functional of density-dependent meson exchange interaction(DDME2)with separable pairing interaction(TMR).Using the multiple deformation constraint,we calculated the potential energy surface(PES)of the uranium isotopes for both even-even and even-odd nuclei with quadrupole and octupole deformation.Based on our calculation and upon comparing the experimental data and Hartree-Fock-Bogoliubov calculations with Gogny D1S calculation data,the ground state of uranium isotopes with reflection-asymmetric deformation was found to be preferred.

Microscopic study of neutron-induced fission process of^(239)Pu via zero-and finite-temperature density functional theory

To study the neutron-induced fission of^(239)Pu,potential energy surface(PES)calculations were performed using zero and finite-temperature density functional theory(FT-DFT)with the Skyrme force.The energy of the incident neutron was simulated by the temperature of the FT-DFT.The variations of the least-energy fission path,fission barrier,total kinetic energy,scission line,and mass distribution of fission fragments with the incident neutron energy were analyzed.It was learned that an increase in the temperature lowers the barrier height,the isomericstate energy,and the ridge between symmetric and asymmetric fission valleys.Additionally,the gaps of the single particle levels become smaller with an increase in the temperature.As the temperature increases,the pre-fission region shrinks,and the scission occurs at smaller deformation around the symmetric fission channel.At low temperatures,the pairing correlations in the collective space are similar to those in zero-temperature DFT,and when the temperature is T>0.3 MeV,the pairing gaps decrease rapidly.Two different methods were used to calculate the fission yields of the neutron-induced fision^(239)Pu(n,)with different incident neutron energies,in the framework of timedependent generator coordinate method(TDGCM).One way to calculate the fission yield of^(239)Pu(n,f)is to solve the collective equation of the TDGCM by using the PES from the FT-DFT with the corresponding temperature.The other involves using the PES from the zero-temperature DFT and adjusting the initial collective energy of the wave packet in the TDGCM according to the incident neutron energy.For the cases of the lower incident neutron energies,these two methods gave similar results and reproduced the experimental peak and width of fission fragment distribution.However,for the highest incident neutron energy considered in this study,the results from the TDGCM using the PES from zero-temperature DFT deviated explicitly from the experimental data,whereas those obtained by using the PES from FT-DFT remained close to the experimental data.This indicated that,with the increase in the incident neutron energy,the shell structure of the compound nuclei changed explicitly;thus,it may not be effective to use the PES from zero-temperature to perform the fission dynamic calculation.

Giant dipole resonance parameters from photoabsorption cross-sections

The structural effect is believed to have no influence on the decay properties of medium and heavy-mass nuclei at excitation energies above the pairing gap.These properties can be described by statistical properties using so-called photon strength functions for different multipolarities,and directly related to the photoabsorption cross-section(σabs).σabs is dominated by the electric giant dipole resonance at y energy εγ≤40 MeV.In this study,we construct two kinds of systematic giant dipole resonance parameters by fitting the experimental photoabsorption crosssections.One is based on the microscopic relativistic quasiparticle random phase approximation approach,whereas the other is estimated by the phenomenological models within the Lorentzian representation.Both of them are demonstrated of efficiently describe the experimental photoabsorption cross-sections available for medium to heavymass nuclei,and they can obtain more reliable predictions for the unknown nuclear system.

Neutron capture cross section of ^(169)Tm measured at the CSNS Back-n facility in the energy region from 30 to 300 keV

The capture cross sections of the ^(169)Tm(n,γ)reaction were measured at the back streaming white neutron beam line(Back-n)of the China Spallation Neutron Source(CSNS)using four C_(6)D_(6) liquid scintillation detectors.The background subtraction,normalization,and correction were carefully considered in the data analysis to obtain accurate cross sections.For the resonance at 3.9 eV,the R-matrix code SAMMY was used to determine the resonance parameters with the internal normalization method.The average capture cross sections of ^(169)Tm for energy between 30 and 300 keV were extracted relative to the ^(197)Au(n,γ)reaction.The measured cross sections of the ^(169)Tm(n,γ)reaction were reported in logarithmically equidistant energy bins with 20 bins per energy decade with a total uncertainty of 5.4%-7.0% in this study and described in terms of average resonance parameters using a Hauser-Feshbach calculation with fluctuations.The point-wise cross sections and the average resonance parameters showed fair agreement with the evaluated values of the ENDF/B-Ⅷ.0 library in the energy region studied.

Energy density functional analysis of the fission properties of^(240)Pu:The effect of pairing correlations

We have calculated the potential energy surfaces for ^(240)Pu up to the scission point using the density functional theory with different pairing strengths to investigate the effect of pairing correlations on its fission properties.An enhancement in the pairing correlations lowers the barrier heights,isomeric state,and ridge between the symmetric and asymmetric fission valleys significantly.Moreover,it weakens the microscopic shell structure around the Fermi surface,shrinks the scission frontiers,especially for the symmetric and very asymmetric fission regions,and lifts the total kinetic energies(TKEs)for the symmetric fission region.It is also emphasized that the microscopic calculation qualitatively reproduces the trend of the distribution of the measured TKEs,especially for the positions of the peaks at A_(frag)≈132 and A_(frag)≈108.