The Influence of Gamma Radiation on The Paint Layers

Zračenje je prijenos energije elektromagnetskim valovima ili česticama. U ovom istraživanju primijenjeno je gama zračenje radiaktivnog izotopa kobalta-60, koje spada u grupu ionizirajućeg zračenja što znači da posjeduje dovoljno energije da ionizira tvari. Na temelju gama zračenja radiaktivnog izotopa kobalta-60, zasniva se fizikalna i beskontaktna radijacijska metoda dezinfekcije i dezinsekcije koja se već nekoliko desetljeća uspješno primijenjuje u saniranju raznovrsnih nametnika i mikroorganizama nastanjenih na organskom materijalu mnogobrojnih umjetnina. Velika prodornost gama zraka osigurava efikasnost i pouzdanost biocidnog djelovanja jer lako prolaze kroz materijale i imaju dovoljno energije za ionizaciju materije zbog čega mogu oštetiti žive stanice u svim fazama njihovog razvoja. Jedini takav izvor gama zračenja (radioaktivnog izotopa kobalta, 60Co) u Hrvatskoj se nalazi u Laboratoriju za radijacijsku kemiju i dozimetriju (LRKD) Instituta Ruđer Bošković. Najvažniji parametar o kojem ovise svi efekti zračenja naziva se apsorbirana doza, D, oznake grej, Gy, koja opisuje povećanje unutrašnje energije u tvari izloženoj ionizirajućem zračenju te označava energiju zračenja koju je primio ozračeni medij. Osim apsorbirane doze važna je i brzina apsorbirane doze, Ḋ [Gy/s], koja ovisi o jačini polja zračenja dok polje zračenja ovisi o aktivnosti izvora. Brzina doze može se podesiti prema potrebi s ciljem da se bira namanja doza za što efikasniju i željenu konzervaciju. Osim, već istraženog, štetnog utjecaja gama zračenja na nametnike, u ovom istraživanju, problematika je usmjerena na moguće štetne utjecaje gama zračenja na veziva i slikani sloj. Odabrano je šest vrsta veziva podijeljenih u dvije skupine s obzirom na kemijsku strukturu, a to su: polisaharidno vezivo, odnosno arapska guma i proteinska veziva u koje spadaju bjelanjak, žumanjak, cijelo jaje, kazein i tutkalo. Veziva su podvrgnuta zračenju dozama od 2, 7, 10, 25 i 100 kGy, a upotrebljene su dvije različite brzine doze zračenja, maksimalna brzina doze kod veziva ozračenih u centru koja je u vrijeme istraživanja iznosila Ḋmax = 7, 695 Gy/s, i manja brzina doze zračenja kod uzoraka ozračenih na udaljenosti od centra, Ḋ = 69,98 Gy/s. Nakon zračenja, na vezivima su mijerene promjene u boji pomoću spektofotometra odmah nakon zračenja i mjesec dana kasnije, te promjene nastale na molekularnoj razini pomoću FTIR uređaja. Kasnije je svih šest navedenih veziva pomiješano s pigmentom olovne bijele te su tako pripremljeni uzorci slikanih slojeva podvrgnuti jednakom tretmanu ozračivanja kao i sama veziva. Nakon ozračivanja tako pripremljenih slikanih slojeva, promatrana je samo promjena boje, također pomoću spektofotometra.Radiation is the transmission of energy by electromagnetic waves or particles. In this study, the gamma radiation of the cobalt-60 radioactive isotope was applied. This type of radiation belongs to the group of ionizing radiation, was applied, which means that it has enough energy to ionize the substance. Based on gamma radiation of the cobalt-60 radioactive isotope, a physical and contactless radiation method of disinfection and disinsection has been established, which for several decades has been successfully applied in the remediation of various pests and micro-organisms inhabited of the organic material of numerous works of art. The high permeability of gamma rays ensures the efficiency and reliability of biocidal action because they easily penetrate materials and have sufficient energy to ionize matter, which can damage living cells at all stages of their development. The only such source of gamma radiation (radioactive isotope of cobalt, 60Co) in Croatia is located in the Laboratory for Radiation Chemistry and Dosimetry (LRKD) of the Rudjer Boskovic Institute. The most important parameter on which all the effects of radiation depend is called the absorbed dose, D (gray, Gy), which describes the increase in internal energy in a substance exposed to ionizing radiation and indicates the radiation energy received by the irradiated medium. In addition to the absorbed dose, the absorbed dose rate, Ḋ [Gy/s], which depends on the strength of the irradiation field, is important, while the irradiation field depends on the activity of the source. The dose rate can be adjusted as needed in order to select the lowest dose for the most efficient and desired conservation treatment. In addition to the already investigated harmful effects of gamma radiation on the unwanted organims, in this research, the problem is focused on the possible harmful effects of gamma radiation on the binders and the paint layers. Six types of binders were selected, divided into two groups according to their chemical structure, polysaccharide binder that is, Arabiac gum and protein binders which include egg white, egg yolk, whole egg, casein and animal glue. The binders were exposed to radiation at doses of 2, 7, 10, 25 and 100 kGy, and two different radiation dose rates were used, the maximum dose rate for binders irradiated at the center, which at the time of the research was Ḋmax = 7, 695 Gy/s, and lower radiation dose rate for the sample irradiated at a distance from the center, Ḋ = 69.98 Gy/s. After irradiation, color changes of the binders were measured by spectrophotometer, immediately after irradiation and one month later. Possible changes in the molecular structure were measured by the FTIR device. Subsequently, all six of these binders were mixed with lead white pigment and thus the prepared sample layers were subjected to the same irradiation treatment as the binders themselves. After irradiation of the layers thus prepared, only the color change was observed, also using a spectrophotometer