Numerical method

ACTINV solves a nuclide network under irradiation and during cooling. For a fixed spectrum and schedule segment, the network is a linear system built from decay constants and spectrum-collapsed reaction rates. Optional feed adds a constant source and removal adds first-order losses with a recorded sink.

Data and rates

The Rust data library reads supported ENDF-6 evaluations and builds deterministic activation libraries. Standard neutron data use 709 groups; standard proton, deuteron, and alpha data use 162 groups at 0 K. A calculation must use the projectile, temperature, and group structure its library declares.

Decay data provide half-lives, branching, energies, and available radiation spectra. Natural elements are expanded using tabulated abundances. Products absent from the configured data remain explicit leakage.

Time integration

The solver uses the Chebyshev Rational Approximation Method, with CRAM orders 16 and 48. The default order is 16. Uncertainty runs evaluate the alternate order as a separately reported method comparison; this comparison is not a proof of total numerical error.

options.mode selects auto, trace, or coupled. Trace mode retains an undepleted initial-material reservoir and a linear production system. Coupled mode evolves the material network. Auto uses an estimated initial-material reaction-loss fraction to select the path and records its decision in the ledger. See the options reference for the exact criterion and pruning choices.

Responses and uncertainty

Activity follows radioactive populations and decay constants. Decay heat combines evaluated alpha, beta, and gamma energy contributions. Photon sources use evaluated decay spectra; response quantities use the explicit photon or radiological tables supplied by the analyst.

First-order sensitivities propagate retained MF=33 covariance into selected responses. Optional decay-constant and independent fission-yield channels use the uncertainties in their evaluated records. Coverage and excluded terms remain explicit; see Results.

Self-shielding and damage

A separate neutron table supplies finite-dilution unresolved-range Bondarenko factors. Fixed or composition-derived dilution selects factors on the declared grid, and compatibility is checked against the library. This bounded method does not provide resolved-region pointwise shielding or a geometry-dependent transport solution.

NRT damage uses separate damage-energy production data and declared displacement energies. It reports coverage of the material targets; it does not model damage covariance, recombination, or general material evolution.

For equations, data-processing details, and historical controls, consult the technical method record. Validation evidence explains what the recorded checks establish.