celeritas::EnergyLossHelper Class Reference

Precalculate energy loss fluctuation properties. More...

#include <EnergyLossHelper.hh>

Public Types
Type aliases
using	FluctuationRef = NativeCRef< FluctuationData >
using	Energy = units::MevEnergy
using	EnergySq = Quantity< UnitProduct< units::Mev, units::Mev > >
using	Mass = units::MevMass
using	Charge = units::ElementaryCharge
using	Model = EnergyLossFluctuationModel
using	Real2 = Array< real_type, 2 >

Public Member Functions
CELER_FUNCTION	EnergyLossHelper (FluctuationRef const &shared, CutoffView const &cutoffs, MaterialTrackView const &material, ParticleTrackView const &particle, Energy mean_loss, real_type step_length)
	Construct from model parameters, incident particle, and mean energy loss.
CELER_FORCEINLINE_FUNCTION FluctuationRef const &	shared () const
	Shared data.
CELER_FORCEINLINE_FUNCTION MaterialTrackView const &	material () const
	Current material.
CELER_FORCEINLINE_FUNCTION Model	model () const
	Type of model to select.
CELER_FUNCTION Energy	mean_loss () const
	Input mean loss.
CELER_FUNCTION Energy	max_energy () const
	Maximum allowable energy loss.
CELER_FUNCTION real_type	beta_sq () const
	Kinematics value: square of fractional speed of light.
CELER_FUNCTION EnergySq	bohr_variance () const
	Bohr variance.
CELER_FUNCTION Mass	two_mebsgs () const
	Kinematics value for electrons: 2 * mass * beta^2 * gamma^2.

Static Public Member Functions
static CELER_CONSTEXPR_FUNCTION Energy	ionization_energy ()
	Atomic energy level corresponding to outer electrons (E_0)

Detailed Description

Precalculate energy loss fluctuation properties.

Fluctuations in the energy loss of charged particles over a given thickness of material arise from statistical variation in both the number of collisions and the energy lost in each collision. Above a given energy threshold, fluctuations are simulated through the explicit sampling of secondaries. However, the continuous energy loss below the cutoff energy also has fluctuations, and these are not taken into account in the calculation of the mean loss. For continuous energy loss, fluctuation models are used to sample the actual restricted energy loss given the mean loss.

Different models are used depending on the value of the parameter \( \kappa = \xi / T_{max} \), the ratio of the mean energy loss to the maximum allowed energy transfer in a single collision.

For large \( \kappa \), when the particle loses all or most of its energy along the step, the number of collisions is large and the straggling function can be approximated by a Gaussian distribution.

Otherwise, the Urban model for energy loss fluctuations in thin layers is used.

Note

This performs the same sampling routine as in Geant4's G4UniversalFluctuation, as documented in section 7.3 in the Geant4 Physics Reference Manual and in PHYS332 and PHYS333 in GEANT3, CERN Program Library Long Writeup, W5013 (1993).

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

• EnergyLossHelper.hh