Calculations of dose equivalent quantities for high-energy neutrons using homogeneous and heterogeneous phantoms

Monte Carlo calculations of fluence-to-dose conversion factors have been performed using the Pacific Northwest Laboratory (PNL) versions of the MIRD-V male and female anthropomorphic phantoms and the International Commission on Radiation Units and Measurements (ICRU) spherical phantom. The phantoms were irradiated with monoenergetic, parallel neutron beams over the energy range from 10 to 180 MeV. The impacts of the new radiation protection quantities recommended in the International Commission on Radiological Protection (ICRP) Publication 60 were explored. Ambient dose equivalents and deep dose equivalent indices were calculated using both the ICRP 21 and ICRP 60 Q-L relationships. The LAHET computer code was utilized to perform the energy deposition calculations for neutrons above 20 MeV. Secondary charged particles are tracked down to 1 MeV in LAHET. Lower-energy neutrons and neutron-induced photons were transported using the HMCNP code and the ENDF/B-V continuous-energy cross-section data library. The results were compared with the limited dosimetric data now available for high-energy neutrons. The ambient dose equivalent and the deep dose equivalent index were found to underestimate the effective dose for energies higher than 50 MeV.