# A Survey of Electromagnetic Techniques Applied to Cultural Heritage Conservation
## 2 EM Techniques Applied to CH
### Radiation Parameters and Dosimetry for CH Application  
When speaking of EM radiations for CH restoration, it must be clearly stated that radiation leads to the breaking of chemical bonds in the irradiated object, and to the release of free radicals or excited species from it [59]; this is the starting point to provide a valuable risk assessment of the use of EM technique for CH preservation. The most vulnerable bonds are the covalent ones, which are typical of living creatures. This is why irradiation is so efficient for disinfection and pest decontamination, but it is also why the irradiation of CH artifacts may be responsible for side effects [14]. When an object is irradiated, two parameters are of the greatest relevance:  
* The absorbed dose;
* The absorbed-dose rate.  
The absorbed dose is defined as \"the mean energy imparted by ionizing radiation to the matter in a volume element divided by the mass of that volume element\" [60] (p. 27), while the absorbed-dose rate refers to \"absorbed dose per unit time\" [14] (p. 44). The importance of these parameters depends on the fact that the radiation must be efficient, yet safe, for the artifact, the environment, and the people around it; hence, the dose of irradiation must be properly evaluated.  
In practice, the absorbed dose considered is an average value, and it is peculiar to the specific material under treatment; the success of the treatment depends on the dose delivered, and this is why dosimetry systems are so important. The classification recalled by IAEA [14] for dosimetry system is ISO/ASTM 51261:2013 [61]. According to this standard, dosimetry systems with the highest metrological qualities are the _primary standard_ dosimetry system, followed by the _reference standard_ one. But the dosimeters used for routine dose measurements are those of the third category, the _routine_ dosimetry system category. These dosimeters are recognized as reliable worldwide for dose mapping and process monitoring. Examples of routine dosimeters are reported in ISO/ASTM 52628 [62] and for each of them, the useful absorbed dose range is reported; this range is an indication of which dosimeter is the best suited for a specific field of application.  
Originally intended for the medical, agricultural, industrial, biological, and food [63; 64; 65; 66] sectors, dosimetry systems are now available for CH applications. As an example, at the gamma irradiation Calliope facility of Casaccia Research Center (Rome, Italy), ionizing radiation treatment are performed for CH objects and different dosimetry systems are available: Fricke solution (20-200 Gy), Red Perspex (5-50 kGy), radiochromic (1 kGy-3 MGy), alanine--ESR (1 Gy-500 kGy), Thermo Luminescent Dosimetry TLD (0.1 mGy-100 Gy), and electronic RADFET (0.01-Gy) [67].  
For a correct use of dosimetry systems for CH applications the following elements must be considered:  
* Size, density, homogeneity or heterogeneity of the artifact;
* Balance between reliability and harmlessness of treatment.  
As for the first point, this has an impact also on the number and location of dosimeters, while the second point results from the dose range window determined by the minimum and maximum values to be considered. The minimum value is related to the concept of reliability, i.e., it is the value which guarantees that the decontamination or consolidation effect is achieved; the maximum value is the one that still preserve the integrity of the irradiated object. According to [PERSON] et al. [68] the maximum safe dose considered is the one valuable for cellulosic materials (among the most sensitive material present in CH objects), while for the minimum value, two different scenario are considered: insect eradication (500 Gy) and fungicidal treatment (6 kGy).