Calculation of quality factors for space radiation at low Earth orbit: Monte Carlo-based microdosimetric approach

This study aims to calculate quality factors (<i>Q</i>) for the radiation environment at low Earth orbit using Monte Carlo-based microdosimetric techniques. This study considers Galactic Cosmic Ray (GCR) ions (<i>Z</i>= 1-28), trapped protons, and albedo neutrons.<i>Q</i>is calculated with (2.8 g cm^-2polyethylene and 10 g cm^-2thick aluminum) and without shielding. FLUKA code is used to model a uniform radiation environment incident on a spherical spacecraft having the above shielding material while a spherical tissue-equivalent proportional counter (TEPC) is positioned at the center of this spherical envelope. The initial fluence spectra of the above radiation fields are based on the OLTARIS code. Microdosimetric distributions in the cavity of the TEPC are calculated separately for GCR ions, trapped protons, and albedo neutrons. Using the microdosimetric distributions,<i>Q</i>values for these radiations including mission<i>Q</i>values are calculated based on the theory of dual radiation action (TDRA) model, and the formalisms based on ICRP60 and ICRU40.<i>Q</i>initially increases with the<i>Z</i>of the ion, but beyond<i>Z</i>= 22, it becomes insensitive to<i>Z</i>. Depending on the calculation model, the mission<i>Q</i>value is in the range of 1.91-2.45 for no shielding, 1.67-2.07 for 2.8 g cm^-2polyethylene shielding, and 1.81-2.48 for 10 g cm^-2aluminum shielding. The microdosimetry-based mission<i>Q</i>values corresponding to 2.8 g cm^-2polyethylene shielding calculated according to the ICRP60 and ICRU40 models compare well with the published measured values of previous space missions. The calculated TDRA-based<i>Q</i>values compare well with the values derived from the OLTARIS code. A significant reduction in the dose equivalent is achieved with 10 g cm^-2Al shielding as compared to 2.8 g cm^-2polyethylene. Overall, the study enhances the understanding of how shielding influences<i>Q</i>and dose equivalent.