Radiation risk management for human space missions depends on accurate modeling of high-energy heavy ion transport in matter. The process of nuclear fragmentation can play a key role in reducing both the physical dose and the biological effectiveness of the radiation encountered in deep space. Hydrogenous materials and light elements are expected to be more effective shields against the deleterious effects of galactic cosmic rays (GCR) than aluminum, which is used in current spacecraft hulls. NASA has chosen polyethylene, CH2, as the reference material for accelerator-based radiation testing of multi-function composites that are currently being developed. A detailed discussion of the shielding properties of polyethylene under a variety of relevant experimental conditions is presented, along with Monte Carlo simulations of the experiments and other Monte Carlo calculations in which the entire GCR flux is simulated. The Monte Carlo results are compared to the accelerator data and we assess the usefulness of 1 GeV/amu 56Fe as a proxy for GCR heavy ions. We conclude that additional accelerator-based measurements with higher beam energies would be useful.
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"Many researchers have measured indirectly the cross sections for various ion-beams of different energies on hydrogen targets     because the use of liquid hydrogen as a target is problematic. Therefore, the chargechanging cross sections on hydrogen targets are calculated using cross sections for both polyethylene and carbon targets    as: r cc ðHÞ ¼ 0:5½r cc ðCH 2 Þ À r cc ðCÞ "
[Show abstract][Hide abstract] ABSTRACT: The depth dose-distributions and partial fragmentation cross sections for 56Fe ions on a polyethylene medium are estimated using Geant4: a Monte Carlo simulation toolkit. The models employed in the present work are the Binary Cascade, Abrasion-Ablation and Quantum Molecular Dynamics. The multifragmentation models, such as statistical multifragmentation and Fermi break-up models are used in combination with the other models to define the nuclear interactions more precisely. The partial fragmentation cross sections are calculated on the basis of charge scored in the detector. The simulated results are validated by comparing with the experimental data.
Full-text · Article · Jun 2014 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
"Even though heavy ions of charge Z = 3–92 are far less abundant (1%) than protons (87%) in galactic cosmic rays (GCR), they are significant importance because of their high relative biological effectiveness (RBE)    . GCR, trapped particles, fragmentation products, recoil nuclei and neutrons cause the major health risk to astronauts , electronics and scientific equipment in a spacecraft      . "
[Show abstract][Hide abstract] ABSTRACT: The depth-dose distribution of a 56Fe ion beam has been studied in water, polyethylene, nextel, kevlar and aluminum media. The dose reduction versus areal depth is also calculated for 56Fe ions in carbon, polyethylene and aluminum using the Monte Carlo simulation toolkit Geant4. This study presents the validation of physics models available in Geant4 by comparing the simulated results with the experimental data available in the literature. Simulations are performed using binary cascade (BIC), abrasion–ablation (AA) and quantum molecular dynamics (QMD) models; integrated into Geant4. Deviations from experimental results may be due to the selection of simple geometry. This paper also addresses the differences in the simulated results from various models.
Full-text · Article · Nov 2012 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
"Nuclear fragments, recoil nuclei as well as neutrons are produced during interaction of particles with shielding materials and tissue-like media (Cucinotta and Durante, 2006; Durante, 1996). Nuclear fragmentation reactions reduce both physical and biological effectiveness of the incident radiations (Guetersloh et al., 2006). Therefore , the complete knowledge of fragmentation reactions will be useful for designing the space shielding materials and hadrontherapy. "
[Show abstract][Hide abstract] ABSTRACT: Study of depth–dose distributions for intermediate energy ion beams in tissue-like media such as polyethylene (CH2)n provides a good platform for further improvements in the fields of hadrontherapy and space radiation shielding. The depth–dose distributions for 12C ions at various energies and for light and intermediate ion beams (3He, 16O, 20Ne and 28Si) as well as for heavy ions 56Fe in polyethylene were estimated by using simulation toolkit: Geant4. Calculations were performed mainly by considering two different combinations of standard electromagnetic (EM), binary cascade (BIC), statistical multifragmentation (SMF) and Fermi breakup (FB) models. The energies of the ion beams were selected to achieve the Bragg peaks at predefined position (∼60 mm) and as per their availability. Variations of peak-to-entrance ratio (from 7.44 ± 0.05 to 8.87 ± 0.05), entrance dose (from 2.89 ± 0.01 to 203.71 ± 0.63 MeV/mm) and entrance stopping power (from 3.608 to 208.858 MeV/mm, calculated by SRIM) with atomic number (Z) were presented in a systematic manner. The better peak-to-entrance ratio and less entrance dose in the region Z = 2 to 8 (i.e. 3He to 16O) may provide the suitability of the ion beams for hadrontherapy.
Full-text · Article · Jun 2012 · Advances in Space Research