An optical and statistical model is what CASTHY is.
Specifically, the model can be found among the Nuclear Energy Agency's data bank of computer program services. The optical model offers calculations of neutron cross-sections in terms of total, shape elastic scattering and compound nucleus formation. The statistical model provides capture, compound elastic, and inelastic cross-sections. The model also supplies calculations for capture gamma-ray spectra and cross-sections of competing processes.
Whatever the calculation, the computer language is Fortran-77 and -90.