Application of the MCNP6.1 code to estimate the directional dependence of radiation protection factor values for a simple surrogate vehicle

Radiation protection factor (RPF) values are relevant to various US defense and civil support organizations. An equation was developed to quantify the angular-dependent protection of a shielding configuration in the presence of a mono-energetic radiation field. Values of ambient dose equivalent, H*(10), were computed with version 6.1 of the Monte Carlo N-Particle Code (MCNP6.1) for more than 70 distinct, mono-energetic, planar photon and neutron fields using both the kerma approximation and energy deposition from primary and secondary radiations. The two computational approaches were compared, and the MCNP6.1 models were then modified to simulate the same radiation fields and compute values of directional dose equivalent, H'(10,α), in a tissue sphere centered inside a surrogate vehicle for 13 angles of incidence. Values of H*(10) and H'(10,α) were recast as energy- and angular-dependent RPF values for the incident field-shielding geometries and tabulated. Examples of implementation are provided, and limitations are discussed. (authors)