Simulation of absorbed doses at organs and tissues of adult and pediatric mesh-type computational phantoms for external neutron exposures

Satoh, Daiki   ; Sato, Tatsuhiko   ; Sato, Kaoru   ; Takahashi, Fumiaki  

Recently, International Commission on Radiological Protection (ICRP) released the mesh-type reference computational phantoms of adult male and female, whose resolutions are much higher than those of conventional voxel phantoms. In addition, the mesh-type pediatric computational phantoms of newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old male and female were constructed by a research group of Hanyang University, Korea, and became available. In this study, we analyzed age-dependent tissue and organ absorbed doses using those mesh-type phantoms for external neutron exposures. The phantoms were incorporated into a general-purpose radiation transport code PHITS, and irradiated by neutrons at 68 energy points from 10 to 10 MeV under 6 ideal irradiation conditions. The simulation results say that the thermal-neutron capture reaction of hydrogen plays an important role below approximately 0.1 MeV and the doses of adults is higher than those of pediatrics because larger body size leads to generating more thermalized neutrons. Above 0.1 MeV, recoil protons from elastic collision of hydrogen are dominant contributor to the doses and doses of pediatrics become larger than those of adults because those protons can reach to deep organs of pediatrics.