THE ROLE OF ACCELERATION FACTOR IN PROTON IRRADIATION TESTS

Abstract

Materials need to undergo qualification testing before being applied to any space mission. Testing includes radiation hardness. It is the aging response of materials to corpuscular and/or electromagnetic radiation. The type of radiation and its amplitude depend on the space environment under study. To perform tests within reasonable times, radiation amplitude must exceed that present in space. Hence, accelerated irradiation tests must be performed. Our main objective is to emphasise potential risks, which may occur upon performing irradiation tests of satellite components with an acceleration factor higher than one. Degradation studies of thin metallized foil with an oxide layer were carried out. The irradiation tests were performed by use of a linear proton accelerator at DLR-Bremen for three different proton flux magnitudes. During the irradiation, the sample surfaces were populated with blisters filled with molecular hydrogen gas. It turns out that the size and the number of blisters depends strongly on the proton flux magnitude. More importantly, we have proven that there exists a threshold of the flux magnitude above which the blistering process is being decelerated. It has direct correlation with the metal oxide layer and its aging condition. The here presented results are important for planning of proton irradiation tests. Too high proton fluxes lead to an acceleration of material degradation that does not reflect the true nature of aging processes as take place in the environment under study. In our case, the presence of the outer aluminium oxide layer has a decisive role in the aluminium degradation process.