Abstract
The work is aimed to analyse doses received by astronauts during next journeys outside the Earth magnetosphere, such as the travels to the Moon and Mars according to future world wide space agencies colonization purposes. These type of missions may lead to many risks to astronauts' health, including particles radiation hazards: here we focus on all the main ionizing radiation sources in outer space, such as Solar Energetic Particles (SEP), Galactic Cosmic Rays (GCR) and Anomalous Cosmic Rays (ACR). Radiation belts and particles trapped inside planets magnetospheres are neglected since the time spent inside them during these journeys is short and in most of the considered celestial bodies they do not exist. First part of the work is devoted to analyse the reasons such that these missions have been seleced, by pointing out the major advantages and drawbacks commonly considered. Afterward, we move wider into the physics behind the radiation phenomena, by studying the radiation sources cited above: where they origins, how they propagate and what kind of worrisomes they may carry to human tissues, as well as by explaining the main role played by the Sun. Consequently, we describe the ionising particles-matter interaction, up to the introduction of the dose approach, as the link between a physical quantity, such as the energy released by the particle inside the matter, and typical stochastic quantities related to radiation exposures, such as early diseases and latent effects. The second part concerns about the use of dose assessment tools already available on-line and in literature suitable for our purposes. In particular, our choice is fallen to the set of tools provided by SPENVIS, which allows the user to choose among different model either concerning Solar Particles or Galactic Cosmic Rays, as well as allowing the user to evaluate empirically the dose received by human tissues under specific mission features. Finally, we decided to develop a further tool able to consider real ionising particle fluences directly recorded by some recent suitable satellite, such as ACE, concerning GCR (where overall periodic table ions are considered), and GOES-constellation satellites, concerning Hydrogen and Alpha particles. The code, named DREADCode, which stands for Dose Radiation Effects and Assessment Distribution Code, is a free-tool availale on internet that allows the user to choose well-defined ranges of time, from satellite data-recording starting point up to the almost present day, in order to assess two different dose values: the Effective Dose and the Ambient Dose Equivalent, according to the currently most used radiation-protection quantities pointed out in literature. This tool has been developed bearing in mind the conservative approach of the problem, as well as keeping the computation as quick as possible: for these reasons, the energy released by particles is being computed using the Bethe-Bloch formula, which obtains macroscopic magnitude results, instead of Monte Carlo simulations, perhaps more precise but quite more expensive from the computational point of view. Moreover, this decision could make the tool suitable for quasi-real time results. Beside time period, the user is able to setup shield material properties and thicknesses, ionising particle preferred source and other parameters, as well as the type of exposure, even though the Isotropic option is often recommended for conservative purposes. Afterward, the code computes how many particles are capable to across the shields, either spacecraft walls or spacesuits textures, and gives as result the Effective Dose or the Ambient Dose Equivalent according to the user's preferences: in the first case, fluence-to-dose conversion coefficients are used, as often acknowledged by literature, while in the latter case another particle-matter interaction assessment is run by using the Sphere Equivalent approach as human tissue reference.