# A Survey of Electromagnetic Techniques Applied to Cultural Heritage Conservation
## 3 EM Techniques for CH Restoration
### EM Techniques for Decontamination of CH
#### 3.1.1 Application of Gamma and X-Ray for Decontamination of CH  
Regarding the physical principle, we have already outlined what is necessary for the scope of this paper in Section 2 and in the introduction of Section 3; here, we immediately go through the application of gamma and X-ray for decontamination treatment. The biological vectors for deterioration process of CH objects are mainly insects and fungi; ionizing radiation is an effective solution in both cases. It must be noted that it is gamma radiation that is primarily used in practice, mainly because of its higher penetration power and, hence, homogeneous irradiation of the artifact. The important parameter to control in order to achieve an efficient biocidal effect while ensuring the artifact's integrity is the absorbed dose. Moreover, the efficacy of irradiation is not invalidated by keeping the object inside a package or container; this is, instead, a way to preserve the object in a decontaminated environment after treatment. The dose used to decontaminate CH artifacts from insects is usually in the range of 0.5-2.0 kGy and 10 kGy for microorganisms, while for the sterilization of medical devices, a dose of 25 kGy is commonly used [14]. The difference in the dose range between medical and CH application may seem huge, but it is easily explained by considering the fact that surgical equipment is meant for a one-time use while CH objects should be preserved for as long as possible. To have a comprehensive view of specific irradiation parameters and of the post-treatment effect associated with them, the experience of Grenoble with its ARC--Nucleart (Atelier de Recherche et de Conservation) in biocidal and consolidation treatments is extremely useful. The data collected in the Center since the early 1970s shows that a dose of 500 Gy is deterministically enough to kill any insect at any life stage within 20 days from treatment and, in the meantime, they are not able to reproduce, and it also seems that their appetite is reduced; hence, higher doses are required only if the degradation process must be immediately stopped [90]. For fungi and molds, the approach is probabilistic; hence, it is not possible to determine such a sharp threshold, but most of them have a D\({}_{10}\) (the necessary dose to reduce their population by a factor of 10) in the range of 0.1-1 kGy. It must be noted that most of the available publications in the field of ionizing radiation for CH are IAEA documents, and are not focused on the disinfection or consolidation process per se, but on research undertaken to understand if, and to what extent, there are induced damages or, better, \"changes\" in the aesthetic and structural characteristics of the artifact [19; 22; 24; 25]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Methods** & **Advantages** \\ \hline Gamma/X-ray 1 radiation & Can penetrate complex, volumetric shapes \\  & Rapidity of treatment \\  & No temperature increase \\ UV-C irradiation & Disinfection of buried/waterlogged \\  & stone artifact \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Relevant methods and their advantages [14; 86]. Although gamma radiations are suitable for basically all objects, negative opinions about their use for transparent objects are presented in [8], recalling how the sensitivity of transparent materials to irradiation was already noted by [PERSON] in 1899, and has been confirmed over the years, culminating in the works by [PERSON] et al. [8; 68; 79; 90; 91]. Adverse effects on glass, not only from gamma rays, but also from X-rays and electron radiation, include color fading--reversible or irreversible--and the formation of defects known as color centers; for these reasons, the use of commercial silicate glass as a routine dosimeter has been investigated [63; 64]. [PERSON] et al. [63] demonstrated that, for measuring doses in the range of 0.1-17 kGy, this type of glass can be a reliable routine dosimeter if calibration is properly performed and environment conditions are controlled.