celeritas::PhysicsParamsOptions Struct Reference

Physics configuration options. More...

#include <PhysicsParams.hh>

Public Types
using	Energy = units::MevEnergy

Public Attributes
real_type	secondary_stack_factor = 3
bool	disable_integral_xs = false
Range calculation
real_type	min_range = 1 * units::millimeter
real_type	max_step_over_range = 0.2
real_type	fixed_step_limiter = 0
Energy loss
real_type	min_eprime_over_e = 0.8
real_type	linear_loss_limit = 0.01
Energy	lowest_electron_energy = Energy{0.001}
Multiple scattering
real_type	lambda_limit = 1 * units::millimeter
real_type	range_factor = 0.04
real_type	safety_factor = 0.6
MscStepLimitAlgorithm	step_limit_algorithm {MscStepLimitAlgorithm::safety}

Detailed Description

Physics configuration options.

Input options are:

• min_range: below this value, there is no extra transformation from particle range to step length.
• max_step_over_range: at higher energy (longer range), gradually decrease the maximum step length until it's this fraction of the tabulated range.
• fixed_step_limiter: if nonzero, prevent any tracks from taking a step longer than this length.
• min_eprime_over_e: energy scaling fraction used to estimate the maximum cross section over the step in the integral approach for energy loss processes.
• linear_loss_limit: if the mean energy loss along a step is greater than this fractional value of the pre-step kinetic energy, recalculate the energy loss.
• lowest_electron_energy: lowest kinetic energy for electrons/positrons
• lambda_limit: limit on the MSC mean free path.
• range_factor: used in the MSC step limitation algorithm to restrict the step size to \( f_r \cdot max(r, \lambda) \) at the start of a track or after entering a volume, where \( f_r \) is the range factor, \( r \) is the range, and \( \lambda \) is the mean free path.
• safety_factor: used in the MSC step limitation algorithm to restrict the step size to \( f_s s \), where \( f_s \) is the safety factor and \( s \) is the safety distance.
• step_limit_algorithm: algorithm used to determine the MSC step limit.
• secondary_stack_factor: the number of secondary slots per track slot allocated.
• disable_integral_xs: for particles with energy loss processes, the particle energy changes over the step, so the assumption that the cross section is constant is no longer valid. By default, many charged particle processes use MC integration to sample the discrete interaction length with the correct probability. Disable this integral approach for all processes.

NOTE: min_range/max_step_over_range are not accessible through Geant4, and they can also be set to be different for electrons, mu/hadrons, and ions (they are set in Geant4 with G4EmParameters::SetStepFunction()).

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The documentation for this struct was generated from the following file:

• PhysicsParams.hh