In planning for long-duration spaceflight, it will be important to accurately model the exposure of astronauts to heavy ions in the Galactic Cosmic Rays (GCR). As part of an ongoing effort to improve heavy-ion transport codes that will be used in designing future spacecraft and habitats, fragmentation cross sections of 28Si have been measured using beams with extracted energies from 290A MeV to 1200A MeV, spanning most of the peak region of the energy distribution of silicon ions in the GCR. Results were obtained for six elemental targets: hydrogen, carbon, aluminum, copper, tin, and lead. The charge-changing cross sections are found to be energy-independent within the experimental uncertainties, except for those on the hydrogen target. Cross sections for the heaviest fragments are found to decrease slightly with increasing energy for lighter targets, but increase with energy for tin and lead targets. The cross sections are compared to previous measurements at similar energies, and to predictions of the NUCFRG2 model used by NASA to evaluate radiation exposures in flight. For charge-changing cross sections, reasonable agreement is found between the present experiment and those of Webber, et al. and Flesch, et al., and NUCFRG2 agrees with the data to within 3 percent in most cases. Fragment cross sections show less agreement between experiments, and there are substantial differences between NUCFRG2 predictions and the data.

Charge-changing and fragment production cross sections at 0 circ have been obtained for interactions of 290 MeV/nucleon and 400 MeV/nucleon carbon beams with C, CH2, Al, Cu, Sn, and Pb targets. These beams are relevant to cancer therapy, space radiation, and the production of radioactive beams. We compare to previously published results using C and CH2 targets at similar beam energies. Due to ambiguities arising from the presence of multiple fragments on many events, previous publications have reported only cross sections for B and Be fragments. In this work we have extracted cross sections for all fragment species, using data obtained at three distinct values of angular acceptance, supplemented by data taken with the detector stack placed off the beam axis. A simulation of the experiment with the PHITS Monte Carlo code shows fair agreement with the data obtained with the large acceptance detectors, but agreement is poor at small acceptance. The measured cross sections are also compared to the predictions of the one-dimensional cross section models EPAX2 and NUCFRG2; the latter is presently used in NASA's space radiation transport calculations. Though PHITS and NUCFRG2 reproduce the charge-changing cross sections with reasonable accuracy, none of the models is able to accurately predict the fragment cross sections for all fragment species and target materials.

Charge-changing and fragment production cross sections at 0 degrees have been obtained for interactions of 290, 400, and 650 MeV/nucleon 40Ar beams, 650 and 1000 MeV/nucleon 35Cl beams, and a 1000 MeV/nucleon 48Ti beam. Targets of C, CH2, Al, Cu, Sn, and Pb were used. Using standard analysis methods, we obtain fragment cross sections for charges as low as 8 for Cl and Ar beams, and as low as 10 for the Ti beam. Using data obtained with small-acceptance detectors, we report fragment production cross sections for charges as low as 5, corrected for acceptance using a simple model of fragment angular distributions. With the lower-charged fragment cross sections, we cancompare the data to predictions from several models (including NUCFRG2, EPAX2, and PHITS) in a region largely unexplored in earlier work. As found in earlier work with other beams, NUCFRG2 and PHITS predictions agree reasonably well with the data for charge-changing cross sections, but do not accurately predict the fragment production cross sections. The cross sections for the lightest fragments demonstrate the inadequacy of several models in which the cross sections fall monotonically with the charge of the fragment. PHITS, despite not agreeing particularly well with the fragment production cross sections on average, nonetheless qualitatively reproduces somesignificant features of the data that are missing from the other models.

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.