engleski

What could happen beyond the use of radiation on cultural heritage

The use of gamma-rays, ions, X-rays, electrons, or neutrons is very common for imaging, characterization, and the preservation of cultural heritage materials. Their use provides, for example, knowledge about their composition, they are used as a biocide of organic materials, or for the consolidation of materials. Concerns about the eventual side-effects (immediate and future) induced by radiation in some of these materials are growing among the different communities involved. It is very important to join the expertise, knowledge, and concerns of each radiation group together with conservators to clearly study the eventual cause (mainly due to physico-chemical mechanisms) of these side effects, which can provoke the loss of critical analytical information. Quite often objects are made of heterogeneous or composite materials, so consequences of radiation on a very well-known material can change when other materials are involved. Also important is the documentation of the radiation procedures performed on the objects, including any potential visual side-effect. Such information can be crucial for future radiation experiments or to monitor changes along time. The known side-effects observed in a wide range of materials shows the importance of investing in more research and interdisciplinary work. Some examples are: - Colour changes in transparent materials due to trapping of electrons in the vicinity of impurities ; - Overdoses of radiation can break bonds, induce cross-linking or temperature effects which can modify important properties of materials and in extreme cases affect their mechanical integrity ; - Formation of radicals, which can trigger undesirable chemical changes, such as oxidation, leading to colour changes or surface erosion. - Radiation dosages for fungicidal treatments (typically 5 to 10 kGy) can generate side-effects in sensitive materials like paper. To avoid over-exposure, the main parameters (the radiation dose and the dose rate) must be carefully controlled during radiation and optimized following the ALARA approach. Also important is to control and register the environmental parameters and experimental conditions (inert gas, vacuum, low temperature, low moisture, etc.) that can effectively mitigate some adverse effects. For documentation purposes, it will be also important to unify and clarify concepts used within different communities. For example, a dose of 1 kGy could be considered high for the “ion beam community” but not high enough for the “gamma-ray community”, and more importantly, their effects on the materials under study can be totally different. In this work, examples of visible side effects induced by different types of radiation will be shown. Possible responsible mechanisms and ways of mitigation will be discussed, also focusing on non-visible side effects and suitable approaches to detect and record them for future analysis. All researchers involved in cultural heritage materials using radiation techniques should be aware of the possible side effects that such materials may suffer from radiation and the consequences for their (future) behaviour. Only by understanding the origin of such effects, it will be possible to create strategies, protocols, and risk analysis prior to exposure. Research programs involving different communities and training programs are needed to raise our understanding and transmit knowledge.

radiation technology ; cultural heritage preservation

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