ESR study of Gamma-ray irradiated synthetic calcium carbonates

Abstract

Nine commercial calcium carbonates, plus 3 calcium carbonates which have been synthesized in the laboratory and 2 natural ones, have been γ-ray irradiated at room temperature. From these 14 samples, 11 are pure calcite, 2 are pure aragonite and 1 is a mixture of calcite and aragonite. Important differences in their ESR spectra are observed. A preheating treatment (up to 600°C) was performed in order to standardize the ESR spectra. After a heating treatment at 600°C for 2 h, all the samples are in the calcite phase; 6 of them mainly exhibit, after γ-ray irradiation, a paramagnetic species with g ∥ = 2.0024 and g b = 2.0037 (CO 3- 3?). A k-value of ≈0.1 for two radiolytic species (one at 2.0052 and the other, anisotropic, at 2.0037 and 2.0024) of three commercial samples of calcite is obtained by means of α-particle irradiation with an 241Am source.