Radiobiological effectiveness of neutrons in space
Abstract
The space radiation environment consists of a wide variety of ion species in a continuous range of energies. Nevertheless, most accelerator-based experiments to measure the biological consequences of the exposure to radiation qualities of interest in space radiation protection have been performed with single beams at fixed energies.Efforts are currently being undertaken to implement simulators of mixed-field for radiobiology experiments. However, the neutral component of space radiation is difficult to reproduce in a ground-based measurement: neutrons are not found free in space in significant amount, but they are produced following nuclear reactions in space vehicle or habitat walls (1), in gas components of the planetary atmosphere (2), and in traversed tissues themselves. Neutrons might be responsible only for a small contribution to the total dose absorbed by astronauts, but their biological effectiveness varies with the energy, and neutron contribution to dose equivalent (or any biologically weighted dose) can be correspondingly higher (with quality factors as high as 20). Neutron data from radiobiological measurements are much varied among different experiments, often available only in the few MeV regions, while space radiation requires dedicated studies also at hundreds of MeV. In this higher energy range, the question of biological effectiveness of neutrons has still to be addressed experimentally.In this context, a theoretical effort to predict neutron biological effectiveness for different exposure scenario is highly desirable. This can be achieved with a comprehensive modeling approach, bringing together transport calculations of neutrons through matter, and the predictive power of track structure approaches for secondary charged particles generated by neutron interactions, up to the evaluation of biological damage induction to a sensitive subcellular target as the nuclear DNA. In this work we discuss and apply possible models for energy dependent neutron RBE (3) (Relative Biological Effectiveness) to neutron spectra of interest in case of astronauts' exposures in space situations, as neutrons inside a space habitat or on the surface of Mars. References:(1) L.H. Heilbronn et al., Neutron yields and effective doses produced by Galactic Cosmic Ray interactions in shielded environments in space, Life Sci. Space Res. 7, 90-99 (2015).(2) Jingnan Guo et al., Measurements of the neutral particle spectra on Mars by MSL/RAD from 2015-11-15 to 2016-01-15, Life Sciences in Space Research, 14, 12-17(2017).(3) G. Baiocco et al., The physical origin of neutron biological effectiveness, Sci. Rep. 6, 34033 (2016).
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.160B