Space Radiation and its Biological Effects

This chapter is intended to provide the major dosimetric features that are needed to draw a picture of which particle types, fluences and doses are required to perform reliable space radiation simulation. Because this picture is far from being complete, please refer for more detailed information to cited literature. The chapter also lists major biological questions that must be solved in order to reduce the uncertainties of risk estimates. The simulation of the radiation field in space is rather difficult due to the mixture of particles needed and by the rather long exposure times required to accumulate significant dose in the human body or the cell system under investigation. A recent paper describes in detail the needs for a GCR simulation [Norbury 2016]. The state of laser-driven heavy ion beams is currently far from providing all particle energies that are present in space. However, it is valuable to employ such laboratory sources providing a range of particles and kinetic energies for space research. The laser-driven case for energetic electron and ion production is in an early stage of development and we can expect useful advancements of this technology. We envisage protons and heavy ions with kinetic energies up to 100 MeV/n for this new laser-driven technique. (see chapters 2, 4 and 5 (Part I) for electron and ion acceleration status with high power lasers). For example many biological investigations require high LET, which means that energies of 20-50 MeV/n (with carbon for example) can be efficient for acquiring missing radiobiological data. Although laser-driven particle fluences can be very high and therefore suited to provide high doses in short time, space reference systems typically require low particle fluences continuously distributed over an extended period. Therefore it can be a challenging task to reduce flux levels using collimator optics. A notable advantage of laser-driven ion sources is there emission characteristics, i.e. the broad angular divergence which reduces fluence quickly over a certain distance from the source and enables large field irradiation in a potentially compact setup. A second key advantage might be the intrinsically broad energy distributions of laser-driven ion sources – so, one can consider irradiating samples with a broad energy spectrum which comes closer to the space environment than an ion beam of well-defined energy at a conventional accelerator. A third key advantage might be the intrinsic capability of the laser-driver to generate multiple synchronous beams with different particles, again better simulating the real space environment if properly controllable. Those potential advantages usher optimism that laser-driven particle sources can expand the experimental toolbox for radiation biological studies. In particular, they can help to close the current gap for facility beam time for radiation biologists to answer the open questions and to reduce the extraordinarily large uncertainties in radiation biology for explorative missions