50 years of French experience in using gamma rays as a tool for cultural heritage remedial conservation

Gamma irradiation processing is a well-established procedure for remedial conservation, capable of arresting biological degradation and, when necessary, applied to consolidate the most fragile artefacts. In Grenoble, France, irradiation of cultural heritage items started 50 years ago and both biocidal irradiation and radio-curing for consolidation have been continuously used on a very wide variety artefacts. Insect eradication is the most common treatment, 500 Gy being the threshold required for their elimination. Doses up to 10 kGy are currently used for fungicide purposes, reducing the worst contamination to a healthy, acceptable level. Particular attention has been paid to potential side effects but experience has shown that the technique can be applied safely on a very large range of material. Consolidation of porous material is obtained by classical vacuum/pressure impregnation of styrene/unsaturated-polyester resin, before curing “in the bulk” by irradiation, known as Nucléart Method. The achieved densification is irreversible but is occasionally justified in some relevant cases. Many cultural heritage artefacts were saved by these techniques, from the most humble to the most prestigious. Today, thanks to international collaboration and knowledge dissemination, notably through IAEA, our understanding and control of side effects has increased and techniques have improved and diversified. Several practical experience of ARC-Nucléart for cultural heritage remedial conservation are reported here. •Gamma irradiation for heritage conservation has been successfully used in France for 50 years.•Biocidal (insecticide and fungicide) treatments are the most used.•Particular attention is paid to side effects.•Radiation-curing resin is used to consolidate porous materials.•Many cultural heritage artefacts have been saved by these techniques.