Modeling of X-ray-induced refractive index changes in poly(methyl methacrylate). |
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Authors: | Birk Andreas Ingo Breunig Karsten Buse |
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Affiliation: | Institute of Physics, University of Bonn, Wegelerstrasse 8, 53 115 Bonn, Germany. andreas@physik.uni-bonn.de |
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Abstract: | The refractive index of bulk poly(methyl methacrylate) samples is modified by X-ray exposure. The intensity of the radiation is distributed over an energy range of 1 to 20 keV with a maximum at 3 keV. For an absorbed dose of about 1 kJ cm(-3), an increase of the refractive index of up to 3x10(-4) is observed. However, for much lower doses of about 10 J cm(-3) a decrease of 4x10(-4) appears. These refractive index changes, as well as the simultaneously arising radiation-induced thickness changes, are detected interferometrically. Based on these observations, on dose calculations, and on literature data, a model is proposed which describes quantitatively the observed refractive index changes. The refractive index increase is caused by a radiation-induced chemical alteration of the polymer composition, while the refractive index decrease is correlated with a decrease of mass density. |
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Keywords: | interferometry polymers radiochemistry refractive index X‐ray irradiation |
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