Degradation of historical paper induced by synchrotron X-ray technical examination

International audienceThis research explores how intrinsic factors such as constituents and degradation state can impact the modifications incurred in aged papers during and after X-ray examination. To this end laboratory model papers, artificially aged, and eighteenth and nineteenth century archival documents, with and without additives (gelatin, calcium carbonate) and iron gallate ink, were exposed to Synchrotron X-ray radiation at doses commonly applied (7 Gy to 4 kGy). The threshold dose of 210 Gy previously shown to incur damage in unaged cotton papers falls in this range. Glycosidic scissions, hydroxyl free radicals, UV luminescence and yellowing were measured immediately after the irradiation, and were monitored over a period of three years. Cellulose depolymerization was lower in the aged papers, as well as in the papers containing calcium carbonate and gelatin, than in the unaged fully cellulosic papers. Compared to the papers with no additives, there were more hydroxyl free radicals in the papers with calcium carbonate and slightly less in the gelatin sized papers. UV luminescence and yellowing both appeared post-irradiation, with a delay of several weeks to months. The papers with iron gallate ink showed limited degradation in the low doses range, most probably due to recombination of the free radicals produced. Doses below 4 kGy did not cause yellowing or UV luminescence of the archival papers within the whole monitoring period. The archival papers in good conservation state depolymerized to the same extent as the model papers, while the most degraded archival papers were less impacted than the latter