Generation of UV-induced radiation defects in calcite

Radiation Defects in Lime Mortars and Plasters Studied by EPR Spectroscopy

“…These centers are detected in an EPR experiment, when the sample is placed in a homogeneous magnetic field and irradiated by a continuous flow of microwaves, which, when resonance condition is fulfilled, entails a transition between two spin states. (Grün 1991;Ikeya 1993Ikeya , 2004 Although the effects of γ radiation on calcium carbonate, especially in the form of calcite, has been investigated very thoroughly (Ikeya 1993(Ikeya , 2004Bahain et al 1994;Callens 1997;Callens et al 1998;Baїetto et al 1999;Polikreti et al 2004;Wencka et al 2005;Kabacińska et al 2017Kabacińska et al , 2019, to our knowledge only our group has analyzed it in lime mortars, first on samples from Sveta Petka church in Budinjak, Croatia (Kabacińska et al 2012), and later from ancient settlement Hippos, Israel (Kabacińska et al 2014b). In these studies, we found several signals generated in lime mortars by γ radiation and examined the dose response curves.…”

“…UV irradiation was performed under air conditions using medium pressure Hg lamp EMITA VP -60 (Farmed, Łodź, Poland) working at 180 W, used without a filter, and lasted from 30 min to 7.5 hr, divided in 4 series with a 1-10-week gap between them. The spectral output of the lamp was in the 238-577 nm range, with main wavelengths 313 nm and 366 nm (spectrum shown in Kabacińska et al 2019; see Supplementary Information). During UV exposure, the samples were placed under the maximum irradiation point, 10.5 cm from the source, and flattened to form a thin layer (∼0.5 mm in thickness) covering the irradiated area.…”

“…In the case of mortars and plasters from Hippos the most likely explanation for the presence of nitrates is the decomposition of organic matter, such as straw added during the manufacturing process and the occurrence of nitrites in the desert evaporates. It is worth pointing out that nitrate impurities are not uncommon even in high-purity CaCO 3 samples (Kabacińska et al 2019).…”

“…Research conducted during the last few years by the main author and coworkers (Kabacińska et al 2014a(Kabacińska et al , 2017(Kabacińska et al , 2019 as well as a few different groups (Bartoll et al 2000;Sato et al 2004;Kundu et al 2005) clearly show that radiation defects can also be generated in calcite, instead of bleached, by UV radiation. Recently (Kabacińska et al 2017(Kabacińska et al , 2019, we proposed a mechanism of UV-induced generation of radiation defects in calcite, based on trapping the "secondary electrons"-electrons freed from non-carbonate traps by the incident UV radiation. These studies were conducted on high-purity calcite samples, which provoked the need to investigate this phenomenon for carbonate materials containing more impurities, occurring in archaeological and geological contexts.…”

“…Since those samples were not suitable for EPR dating, because of their relatively young (for this technique) age, and the collection method (suitable for 14 C, but not for trapped-change dating), we focused only on their physicochemical properties, and not age determination ( 14 C dates can be found in Michalska 2019 andMichalska andPawlyta 2019). Research conducted during the last few years by the main author and coworkers (Kabacińska et al 2014a(Kabacińska et al , 2017(Kabacińska et al , 2019 as well as a few different groups (Bartoll et al 2000;Sato et al 2004;Kundu et al 2005) clearly show that radiation defects can also be generated in calcite, instead of bleached, by UV radiation. Recently (Kabacińska et al 2017(Kabacińska et al , 2019, we proposed a mechanism of UV-induced generation of radiation defects in calcite, based on trapping the "secondary electrons"-electrons freed from non-carbonate traps by the incident UV radiation.…”