298 A . Bouzouita et al .: Radioprotection 2024 , 59 ( 4 ), 296 – 305 Fig . 1 . Geometric setup for the Monte Carlo simulation of dose to organs conversion factors due to gamma radiation emitted from sources uniformly distributed in the ground .
2.4 Monte Carlo simulation and organ doses calculation
The first stage of the Monte Carlo simulation models the soil with optimised geometry for a depth of 2 m and a detection height of 2 m . The lateral extent of the soil is set at 2500 m , with the air modeled as a hemispherical volume with a radius of 2500 m . The simulation geometry with the standing phantom on the ground surface is depicted in Figure 1 . The densities and chemical compositions of air and soil match those from Saito and Jacob ( 1995 ). The air with a density of 1.29 mg cm �3 is composed of 75.5 % N , 23.2 % O and 1.3 % Ar . The soil with a density of 1.6 g cm �3 is composed of 57.5 % O , 2.2 % H , 26.2 % Si , 8.5 % Al and 5.6 % Fe Gamma photons are tracked until they reach a cylinder ( 2 m radius , 2 m height ) around the phantom . Livermore ’ s low-energy electromagnetic models are used in Geant4 , considering Compton scattering , Rayleigh scattering , pair production , and the photoelectric effect ( Agostinelli et al ., 2003 ). In this stage the number of emitted photons varied from 2 10 8 to 5 10 8 photons per primary emission energy to maintain calculation accuracy within 4 % uncertainty . In the second stage of the simulation , gamma photons are emitted at the cylinder ’ s surface according to the phase space variables precalculated in the first stage . These variables consist of the energy , the three coordinates of the direction unit vector and the three cylindrical coordinates of the point of impact of the incident photon . The QGSP _ BIC _ HP Geant4 physics list is used , suitable for energies below 200 MeV that characterize radiation protection , shielding and medical applications ( Agostinelli et al ., 2003 ; Incerti et al ., 2020 ). It includes standard Geant4 electromagnetic physics recommended for photons and charged particles interacting with biological tissues . No physical approximations are made , and particle transport occurs within the voxelbased phantom geometry . A total of 510 7 of photons are emitted for each primary energy of interest . Organ DCFs are calculated based on total energy deposited in the 141 organs of the ICRP110 phantom ensuring 5 % precision . Geant4.11.2.1
software on a Linux Ubuntu 20.4 system with a 12-core Intel Core i7-12700 and 32 GB RAM was used for the simulation .
Organ equivalent DCFs are identical to organ absorbed doses owing to a gamma radiation weighting factor of 1 ( ICRP , 2007 ). The active marrow absorbed dose and the skeletal absorbed dose are determined according to the methods described in ICRP 116 ( ICRP , 2010 ) with the absorbed dose for red bone marrow being the mass-weighted average of doses in the skeleton . The skeleton is divided into the 19 bones and bone groups for which individual data on red bone marrow content and marrow cellularity are given in Publication 70 ( ICRP , 1995 ). This sub-division resulted in 44 different identification numbers in the skeleton : two � cortical bone and spongiosa � for each of the 19 bones ( ICRP , 2010 ). The effective dose rate per activity concentration is calculated as a sex- averaged of the equivalent doses assessed for organ or tissue T of the Reference Male and Reference Female according to :
E ¼ X
H T ðmaleÞþH T ðf emaleÞ w T
; ð2Þ 2
T
where H T ( male ) and H T ( female ) are equivalent doses for tissue T in male and female phantom and w T is the tissue weighting factor for organ T recommended in ( ICRP , 2007 ).
Finally , to improve the language of the present work , the authors used the revision tool REF-N-WRITE version 6 . The authors reviewed and edited the content as necessary after using this tool . The scientific findings and conclusions presented in this work were not produced by generative AI tools . They are the sole product of the authors ' research and analysis . The authors assume full responsibility for the accuracy of the results .
3 Results and discussion
Absorbed dose conversion factors ( DCF ) as a function of gamma radiation energy for various organs of the female