Impact Of Pairing Interactions On The Mass Distribution Of Actinide Fission Fragments

This thesis provides a unified description of three-dimensional potential energy surfaces,static fission paths,fission barriers,and fission fragment mass distributions for the isotopic chains of Pu,Th,and U,using a the exactly solvable Yukawa-Folded mean-field plus stan-dard pairing model.The impact of physical quantities such as paring interaction and temper-ature on the mass distribution of fission fragments is analyzed in detail.The calculation of the potential-energy surface is based on a macroscopic-microscopic model framework,while the shape description during fission is based on a Fourier series expansion method.Based on this,the three-dimensional collective model of the Born-Oppenheimer approximation（BOA）is used to describe the mass distribution of fission fragments.Specifically,the article covers the following topics:The thesis firstly introduces the background and process of nuclear fission,the theoretical models of fission,and the research methods of fission fragment mass distribution.In the theo-retical model section,the thesis describes the shape description method based on Fourier series expansion,and in the macro-micro model framework,the macroscopic energy part adopts the Lublin-Strasbourg-Drop（LSD）model with deformation correction,while the microscopic part considers the Strutinsky shell correction.The micro-correction energy calculation adopts the it-erative algorithm for the exact solution of the standard pairing problem.Furthermore,the thesis introduces the calculation of potential-energy surface related to temperature and the research method of fission fragment mass distribution.In the theoretical calculation section,the Yukawa-Folded mean-field plus standard pairing model is first used to systematically describe the odd-even mass differences and barrier heights of the isotopic chains^236-244Pu,^229-237U and^227-235Th and to determine the values of pair-ing interaction parameters.Taking²⁴⁰Pu as an example,the fission potential-energy surface of²⁴⁰Pu is described,and the fission fragment mass distribution of²⁴⁰Pu is calculated.The impact of pairing interaction parameters on the fission fragment mass distribution of²⁴⁰Pu,²³⁶U,and²²⁶Th is studied and analyzed,as well as the odd-even mass differences of symmetric and asymmetric fission points.The fission fragment mass distribution of²³⁶Pu,^238-242Pu is also calculated.The paper also studies the effects of temperature,zero-point energy₀,and neck breaking probability parameter(9 in the three-dimensional collective model on the fission potential-energy surface and mass distribution of²⁴⁰Pu.Numerical analysis results show that the pairing interaction significantly affects the fis-sion fragment mass distribution.Studies on the fission fragment mass distribution of²⁴⁰Pu,²³⁶U and²²⁶Th reveal that as the pairing interaction is enhanced,the asymmetric distribution of the fission fragment mass distribution decreases,while the symmetric distribution increases.Comparing the theoretical and experimental values of the ground-state binding energy,barrier height,and fission fragment mass distribution for the aforementioned isotopes fission processes,it is found that the effect of the paring interaction changes with the elongation deformation of the nucleus,and different nuclear elongation deformation points require different strengths of pairing interaction.Compared with the barrier height,the fission fragment mass distribution requires a stronger pairing interaction strength for description.The comparison between the odd-even mass difference of the symmetric and asymmetric fission points of²⁴⁰Pu,²³⁶U and²²⁶Th and the experimental values further confirms the above conclusions.On this basis,this paper systematically studies the fission fragment mass distribution of²³⁶Pu,^238-242Pu and the results show that the model can well describe the experimental data.On the other hand,taking²⁴⁰Pu as an example,this paper also analyzes the effect of temperature on the potential-energy surface.The results show that with the increase of temperature,the heights of the inner and outer barriers on the fission path gradually decrease.Finally,the paper analyzes the effects of temperature₀and(9 on the mass distribution in this model.Temperature mainly affects the peak values of asymmetric and symmetric fission of fission fragments,and as the temperature increases,the peak value of asymmetric fission decreases gradually,and the peak value of sym-metric fission increases gradually.The zero-point energy parameter mainly affects the peak value of the fission fragments,and as the zero-point energy parameter increases,the peak value of the fission fragment mass distribution decreases.The neck rupture probability parameter mainly affects the peak position of the heavy peak,as the neck rupture probability parameter increases,the peak position of the heavy peak moves towards the direction of larger fragment masses.