IMPACT OF THE ENDF/B-VIII.0 LIBRARY ON MCNP6.2-COMPUTED AMBIENT AND PERSONAL DOSE EQUIVALENT CONVERSION COEFFICIENTS.

The 2018 release of the Evaluated Nuclear Data File (ENDF)/B-VIII.0 library initiated several examinations of the impact of the revised nuclear data on Monte Carlo models. This study used version 6.2 of the Monte Carlo N-Particle® code (MCNP6.2) with the ENDF/B-VI and ENDF/B-VIII.0 libraries to compute conversion coefficients for fluence-to-ambient and fluence-to-personal dose equivalent from neutron energy groups described by an International Atomic Energy Agency 53-bin structure and 47 monoenergetic neutron sources listed in International Commission on Radiological Protection (ICRP) 74. The MCNP6.2 models with ENDF/B-VI data were validated against results published in 2005 by Veinot and Hertel. Conversion coefficients computed with MCNP6.2 and ENDF/B-VIII.0 slightly underestimated the ICRP 74 values but were within ICRP-specified tolerances and do not justify revising the ICRP coefficients. Conversion coefficients for personal dose equivalent were computed with MCNP6.2 and ENDF/B-VIII.0 at four angles of incidence greater than those available in ICRP 74. These new coefficients are relevant to radiation protection studies of interest to US defence-focused organisations.

DOSE CONVERSION COEFFICIENTS FROM MONOENERGETIC NEUTRONS COMPUTED WITH THE MCNP6.2 CODE IN THE VIP-MAN PHANTOM.

Computational estimates of dosimetric quantities from external exposures to neutron fields are valuable to ongoing radiation protection studies that are of interest to US defense-focused organizations. Conversion coefficients for fluence-to-absorbed dose and fluence-to-effective dose were computed using version 6.2 of the Monte Carlo N-Particle® code (MCNP6.2) in the visible photographic man (VIP-Man) numerical model for 45 monoenergetic neutron fields between 10-9 and 20 MeV under six irradiation geometries. Comparisons to the formative VIP-Man study by Bozkurt et al. revealed excellent agreement. The mean relative difference between our VIP-Man/MCNP6.2-computed and the International Commission on Radiological Protection (ICRP) 116-published absorbed dose conversion coefficients in 14 organs and remainder tissues under all geometries was 4.7%, which is within ICRP-reported variations. The effective dose coefficients computed with VIP-Man/MCNP6.2 were strongly similar to ICRP 116 values in all geometries except for posterior-anterior, where the difference was attributed to shielding of anterior organs by the relatively fatty composition of the VIP-Man phantom.

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.