Study on the Effect of Adipose Tissue on Neutron Dose Evaluation for the Human Body Using Voxel Phantoms with Different Weight.

Abstract: When human body is irradiated by neutrons, the adipose content has a significant impact on the neutron dose and induced 24Na activity. To investigate the effect of human adipose content on the conversion coefficients from 24Na activity to neutron dose, five male adult reference computational phantoms with weights ranging from 73.5 kg to 136.5 kg were used. The Monte Carlo N-particle (MCNP) code was used to calculate the neutron absorbed dose and the yield of induced 24Na in the phantoms irradiated by 252Cf neutrons and monoenergetic neutrons. The results showed that the difference in the conversion coefficients from 24Na activity to neutron absorbed dose among the five phantoms irradiated by 252Cf neutrons with anterior posterior (AP) geometry was ≤23.30%, and this difference was attributed mainly to the neutron absorbed dose, which increases with increasing adipose content. Considering the self-absorption of gamma rays in the human body, the counts of 24Na characteristic gamma rays measured directly by the radiation detector outside of the body have no significant trend varying with adipose content, and the difference in the conversion coefficients from the measured counts to neutron dose among the five phantoms irradiated by 252Cf neutrons with AP geometry was ≤5.25%.