Shielding of relativistic protons |
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Authors: | A Bertucci M Durante G Gialanella G Grossi L Manti M Pugliese P Scampoli D Mancusi L Sihver A Rusek |
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Institution: | (1) Department of Physics and INFN, University Federico II, Monte S. Angelo, Via Cintia, 80126 Napoli, Italy;(2) Department of Biology, University Federico II, Monte S. Angelo, Via Cintia, 80126 Napoli, Italy;(3) Chalmers University of Technology, Applied Physics, Nuclear Engineering, 412-96 Gothenburg, Sweden;(4) NASA Space Radiation Laboratory, Brookhaven National Laboratory, Upton, NY 11973, USA |
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Abstract: | Protons are the most abundant element in the galactic cosmic radiation, and the energy spectrum peaks around 1 GeV. Shielding
of relativistic protons is therefore a key problem in the radiation protection strategy of crewmembers involved in long-term
missions in deep space. Hydrogen ions were accelerated up to 1 GeV at the NASA Space Radiation Laboratory, Brookhaven National
Laboratory, New York. The proton beam was also shielded with thick (about 20 g/cm2) blocks of lucite (PMMA) or aluminium (Al). We found that the dose rate was increased 40–60% by the shielding and decreased
as a function of the distance along the axis. Simulations using the General–Purpose Particle and Heavy-Ion Transport code
System (PHITS) show that the dose increase is mostly caused by secondary protons emitted by the target. The modified radiation
field after the shield has been characterized for its biological effectiveness by measuring chromosomal aberrations in human
peripheral blood lymphocytes exposed just behind the shield block, or to the direct beam, in the dose range 0.5–3 Gy. Notwithstanding
the increased dose per incident proton, the fraction of aberrant cells at the same dose in the sample position was not significantly
modified by the shield. The PHITS code simulations show that, albeit secondary protons are slower than incident nuclei, the
LET spectrum is still contained in the low-LET range (<10 keV/μm), which explains the approximately unitary value measured
for the relative biological effectiveness. |
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