A Monte Carlo model of sea-level neutron background: Directionality, spectra, and intensity

We are developing a model of the cosmic my-induced neutron background at se a-level using the high-energy/Monte Carlo transport code MCNPX. The model a ccounts for and records anisotropy in neutron production from cosmic ray in teractions, as well as the known "ground effect" neutron albedo. Initial re sults with an isothermal, constant density atmosphere in slab geometry show good agreement with experimental data on neutron intensity and low-energy directionality predicted previously. Our model also indicates significant n et downward directionality above the energy range 0.1-1.0 MeV depending on the sea-level material composition.