Module channel 

Neutron channel calculations: wave number, ρ parameter, statistical weights.

Computes channel-level quantities needed for R-matrix cross-section evaluation: the neutron wave number k(E), channel parameter ρ = k·a, and spin statistical weight factors g_J.

SAMMY Reference

• rml/mrml03.f Fxradi: wave number and radius computations
• SAMMY manual Section 2 (kinematics)

Units

All quantities in natural units: energies in eV, lengths in fm.

Key Relations

• k = √(2·μ·E_cm) / ℏc = [AWR/(1+AWR)] × √(2·m_n·E_lab) / ℏc
• ρ = k·a, where a = channel radius
• g_J = (2J+1) / ((2I+1)·(2s+1))

Functions

endf_channel_radius_fm

ENDF-6 §2.2.1 default channel radius (fm).

k_squared

Neutron wave number squared k² in fm⁻².

lab_to_cm_energy

Convert between lab and center-of-mass energy.

pi_over_k_squared_barns

π/k² factor that appears in all cross-section formulas.

rho

Channel parameter ρ = k·a.

statistical_weight

Spin statistical weight factor g_J.

wave_number

Neutron wave number k in fm⁻¹.

wave_number_from_cm

Wave number k_c from reduced mass ratio and center-of-mass kinetic energy.