4 Cross-sections

A cross-sections library in Radiant is represented by the Radiant.Cross_Sections object. Once instantiated, its properties can be configured, and the necessary computations to format for particle transport can be performed.

4.1 Generating Cross-Sections from Physics Models

Radiant provides robust capabilities to produce accurate cross-sections for coupled or uncoupled transport of photons, electrons, and positrons. These cross-sections are derived from physics models and tabulated data. To generate them, several mandatory fields need to be specified:

cs = Cross_Sections()                    # Instantiate the cross-sections library
cs.set_source("physics-models")          # Specify cross-sections generation from physics models
cs.set_materials(material_list)          # Define the list of materials
cs.set_particles(particles_list)         # Define the list of particles
cs.set_energy(10.0)                      # Set the midpoint energy of the highest energy group
cs.set_cutoff(0.001)                     # Set the cutoff energy
cs.set_number_of_groups(10)              # Set the number of energy groups
cs.set_group_structure("log")            # Define the energy group structure
cs.set_interactions(interactions_list)   # Define the list of physics interactions
cs.set_legendre_order(7)                 # Specify the Legendre moments order for scattering cross-sections
cs.build()                               # Compute and build the transfer matrix for transport calculations

where

• material_list is a vector composed of Radiant.Material objects,
• particles_list is a vector composed of Radiant.Particle objects,
• interactions_list is a vector composed of Radiant.Interaction objects,

for example:

material_list = [water]
particles_list = [electron, photon]
interactions_list = [Inelastic_Leptons(),Elastic_Leptons(),Compton()]

Particle-Specific Group Definitions: Radiant supports particle-specific group configurations. The number of energy groups and the energy group structure can differ for each particle. For instance, if three particles are defined, their group settings might be configured as follows:

cs.set_number_of_groups([10,30])                  # Set the number of groups
cs.set_group_structure("log","linear")            # Set the group structure

4.2 Generate Custom Cross-Sections

Radiant provides some custom cross-sections capabilities. To generate them, several mandatory fields need to be specified:

cs = Cross_Sections()                     # Instantiate the cross-sections library
cs.set_source("custom")                   # Specify custom cross-sections
cs.set_materials([mat1,mat2,mat3,mat4])   # Define the list of materials
cs.set_particles([custom_particle])       # Define the list of particles
cs.set_absorption([50.0,5.0,0.0,0.1])     # Define the absorption cross-section per material
cs.set_scattering([0.0,0.0,0.0,0.9])      # Define the scattering (isotropic) cross-section per material
cs.build()                                # Compute and build the transfer matrix for transport calculations

These custom cross-sections capabilities are useful to test discretization schemes.

4.3 Read and Write Cross-Sections from FMAC-M files

Radiant is able to read and to write FMAC-M files. To read FMAC-M files and generate the formatted cross-sections for calculations:

cs = Cross_Sections()             # Instantiate the cross-sections library
cs.set_source("fmac-m")           # Specify the source of data as FMAC-M file
cs.set_file("./fmac_m_file.txt")  # Set the location and name of the FMAC-M file
cs.set_materials([water,al])      # Associate the data with material object.  
cs.build()

To write an FMAC-M file, it simply consists of

cs.write("./fmac_m_file.txt")     # Write the FMAC-M file.