Speaker
Description
Risk prediction in space radiation environments is challenging due to the mixed particle radiation field, especially of charged particle of high energy and charge (HZE) in galactic cosmic rays (GCR). It can be quantified in terms of probability for radiation exposure induced death (REID) from cancer. This approach is strongly based on a track structure of HZE ions determined density of ionization. Direct measurements of the track structure of ions or their prediction by measuring type, energy and fluence of HZE ions during space mission is challenging.
Another quantity, reflecting biological effect of radiation is dose equivalent, H. Microdosimetry is a very useful method to evaluate the dose equivalent of any mixed radiation field (photons, neutrons, ions), without prior knowledge of type of charged particles and their spectra. Regional microdosimetry is based on measuring of the stochastic ionizing energy deposited z, event by event, in a micron sized sensitive volume (SV) with similar dimensions to biological cells stochasticity of which also depends on size of SV and a track structure of ions.
The Centre for Medical Radiation Physics (CMRP), at the University of Wollongong in collaboration with SINTEF has successfully developed silicon on insulator (SOI) microdosimeters based on an array of 3D SVs of micron sizes integrated with readout electronics (also called µ+ probe) which is light weight (less than 0.25kg) and low power operation (less than 10V) [1].
The µ+ probe with “Mushroom” microdosimeter was used to verify various shielding materials of the International Space Station (ISS) wall in response to partial proton energy spectra (70-200)MeV of solar particle events (SPE), trapped and GCR at Paul Scherrer Institute (PSI) proton therapy facility in Switzerland and 400 MeV/u 16O, 400 MeV/u 20Ne, 490 MeV/u 28Si and 500 MeV/u 56Fe ions at Heavy Ion Medical Accelerator (HIMAC) in Chiba, Japan. Aluminium, Kevlar-epoxy, Nextel layers were used to mimic the ISS wall during the experiment. Microdosimetric spectra and related to them average quality factor (Q ̅) and the dose equivalent Hp(0.07) and Hp(10) per unit fluence as a measure of the radiation shielding efficiency were obtained experimentally upstream and downstream of the ISS wall [2]. Additionally, carbon fibre, polyethylene, Perspex with the same areal density of currently used aluminium were investigated for potential improvement of radiation shielding.
The µ+ probe was also able to measure accurately high lineal energy (up to 14MeV/m (Si)) of low energy ions including 7Li, 12C, 16O and 48Ti with ranges below 350 µm in silicon.
This study confirms that the portable µ+ probe with SOI microdosimeter is suitable for measurements the dose equivalent in mixed direct and secondary radiation fields produced by HZE ions typical of GCR and SEE in electronics prediction simultaneously. Good agreement of RBE predicted by SOI microdosimeter and from cell experiment will be presented.
