Module reich_moore 

Multi-formalism cross-section dispatcher.

cross_sections_at_energy is the primary entry point for computing energy-dependent cross-sections from ENDF resonance data. It iterates over all resonance ranges in the data and dispatches each to the appropriate formalism-specific calculator:

All formalisms route through a single dispatch pipeline — cross_sections_on_grid precomputes per-range invariants once, then evaluate_precomputed_range evaluates the correct formalism at each energy. cross_sections_at_energy is a one-call convenience wrapper around the same pipeline. There is exactly one entry point and one evaluator per formalism:

ENDF LRF	Formalism	Evaluator
1	SLBW	slbw::slbw_evaluate_with_cached_jgroups
2	MLBW	slbw::mlbw_evaluate_with_cached_jgroups
3	Reich-Moore	reich_moore_spin_group_precomputed (+ 2ch/3ch)
7	R-Matrix Limited	rmatrix_limited::cross_sections_for_rml_range
URR	Hauser-Feshbach average	urr::urr_cross_sections

Reich-Moore Approximation

In the full R-matrix, all channels (neutron, capture, fission) appear explicitly. The Reich-Moore approximation eliminates the capture channel from the channel space, absorbing its effect into an imaginary part of the energy denominator. This makes the level matrix smaller while remaining highly accurate.

For non-fissile isotopes (like U-238 below threshold), each spin group has only ONE explicit channel (neutron elastic), making the R-matrix a scalar — and the calculation is very efficient.

SAMMY Reference

• rml/mrml07.f Setr: R-matrix construction
• rml/mrml09.f Yinvrs: level matrix inversion
• rml/mrml11.f Setxqx: X-matrix, Sectio: cross-sections
• rml/mrml03.f Betset: ENDF widths → reduced width amplitudes
• SAMMY manual Section II.B.1 (Reich-Moore approximation)

Structs

CrossSections

Cross-section results at a single energy point.

Functions

cross_sections_at_energy

Compute cross-sections at a single energy.

cross_sections_on_grid

Compute cross-sections over a grid of energies.