DDFRG3: Double-Differential FRaGmentation model for Neutron production

A Double-Differential FRaGmentation (DDFRG) model for neutron production from nucleus - nucleus collisions is developed for space radiation applications. DDFRG1 was a previous model developed for production of protons and light ions, and DDFRG2 was a model developed for pion production. A new model (DDFRG3) for neutron production is developed in the present work, and is based upon thermal production of neutrons from the projectile, the target and central fireball sources. The Lorentz-invariant double-differential cross sections are calculated in the various source frames, and are Lorentz transformed to the laboratory frame, resulting in a closed-form analytic formula involving no numerical integration, and which can be run very efficiently in radiation transport codes. The Lorentz-invariant double-differential cross section is then integrated over angle to give the single-differential energy spectral distribution. The DDFRG3 neutron model compares very well to an extensive experimental data set.