A cross section evaluation of neutron induced reactions on^(48)Ti is undertaken using the Unified Monte Carlo-B(UMC-B)approach.The evaluation concentrates on estimating the covariance and the use of the UMC-B allows a...A cross section evaluation of neutron induced reactions on^(48)Ti is undertaken using the Unified Monte Carlo-B(UMC-B)approach.The evaluation concentrates on estimating the covariance and the use of the UMC-B allows avoiding the deficiencies of linear regression brought by the traditional least squares method.Eight main neutron and charged particle emission reactions from n+^(48)Ti in the fast neutron energy region below 20 MeV are studied in this work.The posterior probability density function(PDF)of each neutron cross section is obtained in a UMC-B Bayesian approach by convoluting the model PDFs sampled based on model parameters and the likelihood functions for the experimental data.Nineteen model parameters including level density,pair corrections,optical model and Kalbach matrix element parameter are stochastically sampled with the assumption of normal distributions to estimate the model uncertainty.The Cholesky factorization approach is applied to consider potential parameter correlations.Finally,the posterior covariance matrices are generated using the UMC-B generated weights.The new evaluated results are compared with the CENDL-3.2,ENDF/B-VIII.0,JEFF-3.3,TENDL-2021 and JENDL-5 evaluations and differences are discussed.展开更多
The previously derived Lane consistent dispersive coupled-channel optical model for nucleon scattering on 232Th and 23Su nuclei is extended to describe scattering on even-even actinides with Z=90-98. A soft-rotator- m...The previously derived Lane consistent dispersive coupled-channel optical model for nucleon scattering on 232Th and 23Su nuclei is extended to describe scattering on even-even actinides with Z=90-98. A soft-rotator- model （SRM） description of the low-lying nuclear structure is used, where the SRM Hamiltonian parameters are adjusted to the observed collective levels of the target nucleus. SRM nuclear wave functions （mixed in K quantum number） have been used to calculate the coupling matrix elements of the generalized optical model. The ＂effective＂ deformations that define inter-band couplings are derived from the SRM Hamiltonian parameters. Conservation of nuclear volume is enforced by introducing a dynamic monopolar term to the deformed potential, leading to additional couplings between rotational bands. The fitted static deformation parameters are in very good agreement with those derived by Wang and collaborators using the Weizs^cker-Skyrme global mass model （WS4）, allowing use of the latter to predict cross sections for nuclei without experimental data. A good description of the scarce ＂optical＇experimental database is achieved. SRM couplings and volume conservation allow a precise calculation of the compound-nucleus formation cross sections, which is significantly different from that calculated with rigid-rotor potentials coupling the ground-state rotational band. The derived parameters can be used to describe both neutron- and proton-induced reactions.展开更多
基金Supported by the National Key Research and Development(R&D)Program(2022YFA1602403)Continuous Support Basic Scientific Research Project BJ010261223282。
文摘A cross section evaluation of neutron induced reactions on^(48)Ti is undertaken using the Unified Monte Carlo-B(UMC-B)approach.The evaluation concentrates on estimating the covariance and the use of the UMC-B allows avoiding the deficiencies of linear regression brought by the traditional least squares method.Eight main neutron and charged particle emission reactions from n+^(48)Ti in the fast neutron energy region below 20 MeV are studied in this work.The posterior probability density function(PDF)of each neutron cross section is obtained in a UMC-B Bayesian approach by convoluting the model PDFs sampled based on model parameters and the likelihood functions for the experimental data.Nineteen model parameters including level density,pair corrections,optical model and Kalbach matrix element parameter are stochastically sampled with the assumption of normal distributions to estimate the model uncertainty.The Cholesky factorization approach is applied to consider potential parameter correlations.Finally,the posterior covariance matrices are generated using the UMC-B generated weights.The new evaluated results are compared with the CENDL-3.2,ENDF/B-VIII.0,JEFF-3.3,TENDL-2021 and JENDL-5 evaluations and differences are discussed.
基金Supported by International Atomic Energy Agency,through the IAEA Research Contract 19263the Spanish Ministry of Economy and Competitivity under Contracts FPA2014-53290-C2-2-P and FPA2016-77689-C2-1-R
文摘The previously derived Lane consistent dispersive coupled-channel optical model for nucleon scattering on 232Th and 23Su nuclei is extended to describe scattering on even-even actinides with Z=90-98. A soft-rotator- model （SRM） description of the low-lying nuclear structure is used, where the SRM Hamiltonian parameters are adjusted to the observed collective levels of the target nucleus. SRM nuclear wave functions （mixed in K quantum number） have been used to calculate the coupling matrix elements of the generalized optical model. The ＂effective＂ deformations that define inter-band couplings are derived from the SRM Hamiltonian parameters. Conservation of nuclear volume is enforced by introducing a dynamic monopolar term to the deformed potential, leading to additional couplings between rotational bands. The fitted static deformation parameters are in very good agreement with those derived by Wang and collaborators using the Weizs^cker-Skyrme global mass model （WS4）, allowing use of the latter to predict cross sections for nuclei without experimental data. A good description of the scarce ＂optical＇experimental database is achieved. SRM couplings and volume conservation allow a precise calculation of the compound-nucleus formation cross sections, which is significantly different from that calculated with rigid-rotor potentials coupling the ground-state rotational band. The derived parameters can be used to describe both neutron- and proton-induced reactions.
