Establishing the irradiation dose for paper decontamination

Museums, libraries and archives are preserving documents that are slowly degrading due to the inherent ageing of the cellulose substrate or to the technological errors of the past (acid paper, iron gall ink). Beside this, large quantities of paper are rapidly damaged by biological attacks following natural disasters and improper storage conditions.The treatment of paper documents with ionizing radiation can be used for mass decontamination of cultural heritage items but conservators and restaurators are still reserved because of the radiation induced degradation.We conducted a study for establishing the dose needed for the effective treatment of paper documents, taking into account the biological burden and the irradiation effects on paper structure. We used physical testing specific to paper industry and less destructive analytical methods (thermal analysis).Our results show that an effective treatment can be performed with doses lower than 10 kGy. Old paper appears to be less affected by gamma radiation than recent paper but the sampling is highly affected by the non-uniform degree of the initial degradation status. The extent of testing for degradation and the magnitude of acceptable degradation should take into account the biological threat and the expected life time of the paper documents.

RESEARCH HIGHLIGHTS
► For doses <15 kGy, the measurement uncertainty of mechanical properties is higher than the radiation induced degradation.
► The statistics of measuring induced degradation may be improved by testing both mechanical properties and thermal decomposition of paper.
► Because of the large variability of paper samples, testing to only one irradiation dose has no or reduced relevance.
► It was choused for the irradiation of paper items from archives and collections a dose range of 5–7 kGy.