Enum MeanFreePath 

pub enum MeanFreePath {
    Constant,
    EnergyDependent {
        min_cm_angle_rad: f64,
    },
}

How free-flight lengths and the impact-parameter limit are chosen.

Variants

Constant

Constant flight length l = N^(-1/3) (the mean interatomic distance) and impact parameters uniform over a disc of radius p_max = (pi N^(2/3))^(-1/2), so that N pi p_max^2 l = 1: each flight sweeps exactly one atom’s worth of target. This is the amorphous-target convention of Biersack and Haggmark, Nucl. Instrum. Methods 174 (1980) 257. To avoid every primary making its first collision at the same depth l cos(theta_in), the primary’s first flight is R l with R uniform in [0, 1); recoils start at an atom site and fly a full l. Collisions with p > p_max are dropped unless BcaConfig::weak_collisions adds them (module docs, “Weak collisions”).

EnergyDependent

Energy-dependent free path with Poisson-distributed flight lengths. Collisions deflecting by less than min_cm_angle_rad (centre-of-mass) are neglected: for each element i, p_i(E) is the impact parameter at which the centre-of-mass angle equals that minimum, capped at the constant-convention p_max (so the free path is never shorter than N^(-1/3)). The mean free path is lambda = 1 / (N pi Sum_i x_i p_i^2), the flight length is exponential with that mean, the partner is drawn with probability x_i p_i^2 / Sum_j x_j p_j^2, and p = p_i sqrt(R). This is the standard cross-section cut-off treatment of a Poisson collision process (Eckstein 1991). It reduces to Constant (with exponential instead of fixed flight lengths) when every p_i hits the cap. The nuclear energy loss of the neglected small-angle collisions is dropped, so choose the minimum angle small; and since p_i never exceeds the constant-convention p_max, collisions beyond it are dropped too, as in Constant without weak collisions (which this variant does not support).

Fields

min_cm_angle_rad: f64

Smallest centre-of-mass deflection treated as a collision, radians, in (0, pi).

Trait Implementations

impl Clone for MeanFreePath

fn clone(&self) -> MeanFreePath

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for MeanFreePath

impl Debug for MeanFreePath

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for MeanFreePath

fn eq(&self, other: &MeanFreePath) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for MeanFreePath