Galactic Cosmic Ray Exposure of Humans in Space - Influence of galactic cosmic ray models and shielding on dose
calculations for low-Earth orbit and near-Earth interplanetary space
The radiation environment in space is one of the primary concerns for human
spaceflight as it poses potential risk to astronauts’ health. Galactic Cosmic Rays
(GCR), consisting of high-energy nuclei, are a major source of radiation exposure in
space. As the number of people visiting space in low-Earth orbit is increasing and
mankind prepares to go beyond, the issue of radiation protection against GCR thus
becomes vitally important.
The pre-flight assessment of radiation-related health risks is achieved by performing
numerical simulations of the mission scenario to estimate the necessary radiation-dose
quantities. This technique requires models describing the radiation spectra, the target
and shield configurations, and additionally transport codes to simulate the passage of
radiation through matter. The reliability of the calculated dose therefore depends on
the accuracy of all these models.
During the course of this PhD work, commonly used models describing the GCR
spectra are evaluated for their accuracy for various time periods. The model spectra
of nuclei, most relevant for space dosimetry, are compared with measurements
from high-altitude balloon flights and space missions. The GCR models included
in this work are CREME96, CREME2009, Burger-Usoskin, Badhwar-O’Neill2010,
Badhwar-O’Neill2011, Matthiä-ACE/OULU and SPENVIS/ISO15390. The influence
of using these different GCR models on the dose calculations is studied for a time
period ranging over the last four decades. This is achieved by calculating the absorbed
dose and dose equivalent rates in a spherical water phantom using the GEANT4
Monte-Carlo framework. Additionally, the influence of aluminium shielding of varying
thicknesses (0.3 g/cm², 10 g/cm² and 40 g/cm²) on the dose is investigated for a
time period ranging from 1997 to 2012. All these investigations are performed for
near-Earth interplanetary space and the orbit of the International Space Station (ISS).
Apart from examining these parameters the effective dose, being the baseline quantity
for radiation-risk assessment, is estimated. The quantity is calculated for the end of the
year 2009 when the highest GCR intensity since the dawn of human spaceflight era was
observed. Further studies presented in the thesis include the relative contribution of
particles with different energies to the total exposure and the comparison of calculated
dose with the measurements conducted inside the ISS and in-transit to Mars by the
MSL/RAD instrument
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