Study On Deep Space Radiation Transport And Radiation Damage In Materials

With the development of deep exploration, the hazards of space radiation to crews in traveling to moon and mars play the dominant role. In case of mars mission, in which crews spend most of the time outside the earth's magnetic field, galactic cosmic rays(GCR) and solar particle event(SPE) are main exposure concerns. The accumulation of exposures to GCR ions can significantly increase the risk of cancer to astronaut and the SPE can deliver a potentially lethal dose in a few hours'time. So radiation protection is essential and central significance in exploration scenario.The topics of this paper include deep space radiation environment modeling, radiation transport, material protection and damage, which have been recognized as four critical issues in space radiation protection system.First, GCR model which is CREME-96 and SPE model which is a data fitting model are used for deep space radiation analysis. Thereafter, two space radiation transport codes, Heavy Ion Dosimetry(HID) and Deep Space Radiation Analysis(PSR), are developed based on Geant4 Monte Carlo toolkit. Nuclear reaction model– abrasion-ablation model is adopted in HID code which refines the calculation results as dose, energy deposition, et al. Heavy ion induced fragments is analyzed in case of high energy heavy ion pass through biological material and space protection materials. PSR code is aim to deal with space radiation transport in atmosphere and magnet of the planet. It can be used for planet radiation analysis in deep space by renewing the database of the planet and particle transport data. These two codes are encapsulated and windows operating interface and can operated under both Linux and windows system to meet the need of different people.Heavy ion fragments, organ dose and neutron flux are considered as three main aspect in space radiation protection material assessment. All the evaluation aspects do claim and verify that liquid hydrogen is the optimal material among typical space radiation protection materials as water, polyethylene and aluminum. And in deep space, protection efficiency decreases as shielding thickness increases for heavy ions.Heavy ion track is connected to radiation damage. A kind of polymer material called CR-39 is chosen as protection and biological equivalent material. The experiment is done in china institute of atomic energy in which silicon ion with the energy of 100 MeV is supplied. After irradiation, heavy ion tracks is displayed by chemical etching and observed under atomic force microscope (AFM). AFM is a relatively new and fine tool to get the images of tracks in nanometer size. As a result, a new track etch rate parameter is defined to model the track development. The track core size is determined after second etching. And then local dose in the track core is calculated by theδ-ray theory. Track etch rate and etch rate are derived after minute etching from three dimensional track structure. In addition, it is found that the micro-track development model violets the traditional model. And it is the micro-track development model that can explain the relationship between micro-track and material damage.