Nexus-NRS (Nuclear Reaction Suite): Open Functional-Programming Software for Nuclear Reaction Modeling with DWBA—Design and Validation

Nexus-NRS is an open, reproducible software tool for nuclear reaction calculations, implemented in a functional-programming style (Clojure); the underlying reaction theory is standard and pre-established, and the contribution here is the software: stable radial solvers for weakly bound (halo) states, scattering observables, and transfer reactions, packaged with optical-model potentials, Riccati–Numerov integration with regular near-origin initialization options, discrete Wronskian diagnostics for numerical stability, and a Distorted Wave Born Approximation (DWBA) implementation for single-nucleon transfer in the post form, extended with Austern-style multipole/angular ingredients. We report concrete validation results, with figures: near-origin Numerov starts (hybrid vs. finite) agree to better than 10−9 on a 11Be halo bound-state observable, discrete Wronskian drift is reduced by a factor of ∼6–7 by the hybrid start, and a single-threaded partial-wave scan runs within a factor of ∼1.4 of an equivalent NumPy implementation. We compare directly against DWUCK4 for 16O(d,p)17O radial integrals (same order of magnitude, residual disagreement diagnosed but not yet resolved), and against experimental data for 11Li(p,d)10Li populating an unbound p1/2 resonance, where an unfitted (S=1) quasi-bound-resonance DWBA calculation is tested against seven measured points with error bars. With the normalization absorbed into a single scale factor, it reproduces the shape over the forward angular range (χν2=2.1) but not over the full range (χν2=7.4). Nexus-NRS supports scripting/REPL-driven studies and an interactive web dashboard, of which a publicly accessible instance is deployed.