Radioprotection for Astronauts' Missions: Numerical Results on the Nomex Shielding Effectiveness

Abstract

Space missions with humans expose the crews to ionizing radiation, mainly due to the galactic cosmic radiation (GCR). All radiation protection programs in space aim to minimize crews' exposure to radiation. The radiation protection of astronauts can be achieved through the use of shields. The shields could serve as a suit to reduce GCR exposure and, in an emergency, as a radiation shelter to perform necessary interventions outside the space habitat in case of a solar proton event (SPE). A space radiation shielding that is suitable for exploration during space missions requires particular features and a proper knowledge of the radiation type. This study shows the results of numerical simulations performed with the Geant4 toolkit-based code DOSE. Calculations to evaluate the performance of Nomex, an aramidic fiber with high mechanical resistance, in terms of dose reduction to crews, were performed considering the interaction between protons with an energy spectrum ranging from 50 to 1100 MeV and a target slab of 20 g/cm². This paper shows the properties of secondary products obtained as a result of the interaction between space radiation and a Nomex target and the properties of the secondary particles that come out the shield. The results of this study show that Nomex can be considered a good shield candidate material in terms of dose reductions. We also note that the secondary particles that provide the greatest contribution to the dose are protons, neutrons and, in a very small percentage, α-particles and Li ions.

Keywords: Geant4; Nomex; galactic cosmic radiation (GCR); monte carlo; radiation protection; shield; space radiation.

Figure 1

The galactic cosmic rays’ composition.

Figure 2

A schematic view of the geometry of the experimental setup used in the simulation. (left) GCR spectrum; (right) a 20 g/cm² thick Nomex target and the tissue-equivalent ionization chamber at 1.5 cm from the Nomex target [18].

Figure 3

(a) Energy spectrum for the secondary products in the Nomex target normalized to the total yield; (b) computed atomic and mass numbers (Z, A) of the secondary products produced in proton–Nomex interaction for the GCR proton energy spectrum; (c) computed atomic numbers and event frequency of the secondary products produced in the proton–Nomex interaction for the GCR proton energy spectrum. The three clusters of high (1), middle (2), and low (3) masses are highlighted; (d) computed atomic number and energy (Z, E) of the secondary particles produced in the proton–Nomex interaction for the GCR proton energy spectrum [18].

Figure 4

(a) Energy spectrum for the secondary products, normalized to the total yield that leaves the target and arrives at the ionization chamber; (b) computed atomic and mass numbers (Z, A) of the secondary particles that leave the target and arrive at the ionization chamber; (c) computed atomic numbers and event frequency of the secondary particles that leave the target and arrive at the ionization chamber; (d) computed atomic number and energy (Z, E) of the secondary particles that leave the target and arrive at the ionization chamber [18].

Figure 5

Energy spectra for the main secondary products that leave the target and arrive at the ionization chamber. Each spectrum is independently normalized to the total yield (y).