DEGRADATION OF MATERIALS UNDER THE ACTION OF SOFT X-RAY RADIATION FROM SOLAR FLARES

摘要

An estimation of the influence of ionised radiation of solar flares on spacecraft material was made. The main part of the energy of solar flares lies in the range of soft X-ray radiation, i.e. 0.1-10 KeV. The predominant energy contribution comes from photons with energy between 1 and 3 KeV. An evaluation of the interaction of soft X-ray radiation with materials was made. There is a dependency between the total energy absorption of a material and its elementary composition. Evaluation of absorption coefficients for different material depending on photon energy is given. Polymer-building elements such as Fluorine and Silicon possess much higher absorbing coefficients than Carbon and Oxygen. Modelling of dose distributions in materials have shown that the absorption of soft X-ray radiation has an extremely non-homogenous nature. Namely, for energy of photons 1-3 KeV the absorbed dose varies through three orders of magnitude over a depth of 20 urn in case of Teflon FEP while this depth is 5-8 mm for SiC, SiO2 and SiC materials. An extremely high energy absorption peak is observed in a skin layer with a thickness of 1.5± 0.5 micron. The post flight measurements of mechanical and spectroscopic properties of Teflon FEP samples, and analysis of the exposure environment show that the low energy part of the X-ray radiation from the solar flares plays a major role in the degradation of Teflon in space.