Short and long term effects of X-ray synchrotron radiation on cotton paper.

X-ray analytical techniques are increasingly used to study manuscripts and works of art on paper, whether with laboratory equipment or synchrotron sources. However, it is difficult to anticipate the impact of X-ray photons on paper and cellulose-based artefacts, particularly due to the large variety of their constituents and degradation levels, and to the subsequent material multiscale heterogeneity. In this context, this work aims at developing an analytical approach to study the modifications in paper upon SR X-ray radiation using analytical techniques, which are fully complementary and highly sensitive, yet not frequently used together. At the molecular scale, cellulose chain scissions and hydroxyl free radicals were measured using chromatographic separation techniques (SEC-MALS-DRI and RP-HPLC-FLD-DAD), while the optical properties of paper were characterized using spectroscopy (UV luminescence and diffuse reflectance). These techniques showed different sensitivity towards the detection of changes. The modifications in the cellulosic material were monitored in real time, within a few days, and up to two years following the irradiation in order to define a Lowest Observed Adverse Effect Dose (LOAED). As paper is a hygroscopic material, the impact of the humidity in the environment was studied using this approach. Three levels of moisture content in the paper, achieved by conditioning the samples and irradiating them at different relative humidity, were studied (0%, 50%, 80% RH). It was shown that very low moisture content accelerated the molecular and optical modifications.