Astronaut dose coefficients calculated using GEANT4 and comparison with ICRP123

Abstract

Fluence-to-dose conversion coefficients are fundamental ingredients to calculate astronaut radiation dose in space. For this purpose, the conversion coefficients for isotropic radiation provided by the International Commission on Radiological Protection in Publication 123 (ICRP123) are widely used. Understanding the uncertainties in these coefficients is important for a precise calculation of radiation dose. In this work, we present a systematic study of unshielded dose coefficients calculated by means of the GEANT4 Monte Carlo simulation toolkit and the human voxel phantoms defined in ICRP Publication 110. Four GEANT4 physics lists, featured with two variations of electromagnetic and two variations of hadronic interaction models, were used in the study. Absorbed dose and dose equivalent coefficients with both the ICRP60 and NASA quality factors were calculated, for individual cosmic nuclei with charge from Z $=$ 1 to Z $=$ 28 and a kinetic energy range from 1 MeV/n to 100 GeV/n. The effective dose equivalent rates in free space at 1 AU were then calculated for each set of dose coefficients. The four effective dose equivalent rates calculated with each physics list agreed within $\pm 3\%$ , and on average they were larger than the ICRP123 results by $\sim 7\%$ and $\sim 1\%$ using the ICRP60 and the NASA quality factor, respectively. These results shed light on the systematic uncertainty of astronaut radiation exposure calculation, particularly from the physics interaction models.

Keywords: Dose conversion coefficient; Galactic cosmic ray; Linear energy transfer; Monte Carlo simulation; Space radiation.

Fig. 1

$w_{\text{T}}$-weighted sum of fluence-to-absorbed-dose conversion coefficients, $(D/\mathrm{\Phi })={\sum }_{\text{R}}{w}_{\text{T}}(D_{\text{T,R}}/{\mathrm{\Phi }}_{\text{R}})$, for five GCR ions (black: protons, red: helium, orange: oxygen, green: silicon, and blue: iron), calculated separately for the male (left panels (a, c)) and female (right panels (b, d)) phantoms with four GEANT4 physics lists: QBBC (QB, joined filled circles), FTFP$\_$BERT (FT, joined filled triangles), QBBC$\_$ATIMA (QBA, joined empty circles), and FTFP$\_$BERT$\_$ATIMA (FTA, joined empty triangles). For each phantom the coefficients in the kinetic energy range from 1 MeV/n to 100 GeV/n are shown in the upper panels (a, b). The corresponding ratios with respect to the average coefficients of the four GEANT4 physics lists, $\overline{(D/\mathrm{\Phi })}$, are shown in the lower panels (c, d)

Fig. 2

Effective dose equivalent coefficients using the ICRP60 quality factor, ${(DQ/\mathrm{\Phi })}_{\text{ICRP60}}={\sum }_{\text{R}}{w}_{\text{T}}(D_{\text{T,R}}{Q}_{\text{ICRP60}}/{\mathrm{\Phi }}_{\text{R}})$, for five GCR ions (black: protons, red: helium, orange: oxygen, green: silicon, and blue: iron), calculated separately for the male (left panels (a, c)) and female (right panels (b, d)) phantoms with four GEANT4 physics lists: QBBC (QB, joined filled circles), FTFP$\_$BERT (FT, joined filled triangles), QBBC$\_$ATIMA (QBA, joined empty circles), and FTFP$\_$BERT$\_$ATIMA (FTA, joined empty triangles). For each phantom the coefficients in the kinetic energy range from 1 MeV/n to 100 GeV/n are shown in the upper panels (a, b). The corresponding ratios with respect to the average coefficients of the four GEANT4 physics lists, $\overline{{(DQ/\mathrm{\Phi })}_{\text{ICRP60}}}$, are shown in the lower panels (c, d)

Fig. 3

Effective dose equivalent coefficients using the $Q_{\text{NASA}}$ quality factor, ${(DQ/\mathrm{\Phi })}_{\text{NASA}}={\sum }_{\text{R}}{w}_{\text{T}}(D_{\text{T,R}}{Q}_{\text{NASA}}/{\mathrm{\Phi }}_{\text{R}})$, for five GCR ions (black: protons, red: helium, orange: oxygen, green: silicon, and blue: iron), calculated separately for the male (left panels (a, c)) and female (right panels (b, d)) phantoms with four GEANT4 physics lists: QBBC (QB, joined filled circles), FTFP$\_$BERT (FT, joined filled triangles), QBBC$\_$ATIMA (QBA, joined empty circles), and FTFP$\_$BERT$\_$ATIMA (FTA, joined empty triangles). For each phantom the coefficients in the kinetic energy range from 1 MeV/n to 100 GeV/n are shown in the upper panels (a, b). The corresponding ratios with respect to the average coefficients of the four GEANT4 physics lists, $\overline{{(DQ/\mathrm{\Phi })}_{\text{NASA}}}$, are shown in the lower panels (c, d)

Fig. 4

Ratios relative to the ICRP123 coefficients for the coefficients averaged over the four GEANT4 physics lists in this work for five GCR ions (black: protons, red: helium, orange: oxygen, green: silicon, and blue: iron): a, b absorbed dose coefficient ${(D/\mathrm{\Phi })}^{\text{ICRP123}}$, c, d effective dose equivalent coefficient using the ICRP60 quality factor ${(DQ/\mathrm{\Phi })}_{\text{ICRP60}}^{\text{ICRP123}}$, and e, f effective dose equivalent coefficient using the NASA quality factor ${(DQ/\mathrm{\Phi })}_{\text{NASA}}^{\text{ICRP123}}$

Fig. 5

Dose equivalent rates ${\dot{H}}_{\text{T}}$ of 15 sensitive organs/tissues at January 2010 (maximal radiation, left panel) and February 2014 (minimal radiation, right panel), using the ICRP60 (upper panel) and the NASA (lower panel) quality factors, respectively. ${\dot{H}}_{\text{T}}$ values were calculated with the coefficients obtained from four GEANT4 physics lists: QBBC (red), FTFP$\_$BERT (orange), QBBC$\_$ATIMA (green), and FTFP$\_$BERT$\_$ATIMA (blue). For comparison, ${\dot{H}}_{\text{T}}$ calculated with the ICRP123 coefficients (black) are also shown

Fig. 6

Effective dose equivalent rate ${\dot{H}}_{\text{E}}$ during July 2006 and October 2019 using a ICRP60 and b NASA quality factors. They were calculated with the coefficients obtained using four GEANT4 physics lists: QBBC (QB, red filled circles), FTFP$\_$BERT (FT, orange filled triangles), QBBC$\_$ATIMA (QBA, green empty circles), and FTFP$\_$BERT$\_$ATIMA (FTA, blue empty triangles). Also shown are the effective dose equivalent rate calculated with the ICRP123 coefficients ${\dot{H}}_{\text{E}}^{\text{ICRP123}}$ (black squares). The corresponding ratios of rate ${\dot{H}}_{\text{E}}/{\dot{H}}_{\text{E}}^{\text{ICRP123}}$ and their average (black crosses) are shown in (c, d), respectively. As seen, the dose equivalent rates using the four physics lists agree with each other within $\pm 3\%$ for both quality factors. Their averages are larger than the ICRP123 results by $\sim 7\%$ using the ICRP60 quality factor, and by $\sim 1\%$ using the NASA quality factor