Structural studies and optical properties of pearl nucleus irradiated by γ-ray

Abstract

The effect of γ-ray irradiation on the color and structure of the nucleus and cultured pearl nucleus is studied experimentally. By using a (60Co) γ-ray irradiator, the nucleus originating from freshwater shell is irradiated. Consequently, the color of the nucleus is altered from white to blackish brown or gray by an increase in the irradiation dose treatments. The structural identification of all samples has been confirmed using X-ray diffraction. It is clearly found that all the samples are composed of aragonite, a common phase of the mineral CaCO3. A slight change in the crystallinity of the sample is observed when irradiated with high dose of radiation. Scanning electron microscopy images show that there are no morphological changes by irradiation. UV–Vis spectroscopic measurement is used to distinguish and analyze the change of color due to different irradiation doses. With an increase in the γ-ray radiation doses, a red shift in the absorption edge of the optical spectra of pearl nucleus is observed. Electron spin resonance signal shows mainly the presence of radiation-induced radicals as color center defects within the samples. An increase in the defects with a gradual increase in the radiation dose depicts that the defect-level transition is the dominant mechanism for the color change in the pearl nucleus.