Natural radioactivity in Italian ceramic tiles

¹ Interdepartmental Centre for Environmental Science Research, Bologna University, via S.Alberto 163, 48100 Ravenna, Italy
² Department of Physics, Bologna University, Viale Pichat 6/2, 40127 Bologna, Italy
³ Solid State and Radiation Physics Lab., Department of Physics, Bharathiar University, 641 046 Coimbatore, India
⁴ Italian Ceramic Centre, via Martelli 26, 40138 Bologna, Italy

Abstract

Zircon is the mostly widely occurring zirconium-containing mineral mined commercially. Thorium and uranium may substitute for zirconium in the zircon crystal lattice. The radioactivity levels in zircon lies typically within the ranges 500–1000 Bq kg^-1 for ²³²Th and 1000–5000 Bq kg^-1 for ²³⁸U [1]. One of the most important use of zircon is as opacifier for ceramic tiles. Body of ceramic tiles is a mixture of different raw materials, including: clays, quartz materials and feldspathic materials. The body may be glazed or left unglazed. Due to the presence of zircon in the glaze or in the body, ceramic tiles can show natural activity concentration significantly higher than the average values of Earth's crust. This study contains a summary of results obtained by a survey on Italian ceramic tiles collected over three years (2005–2007). About one hundred ceramic tiles were analysed. The survey consisted of measurement of ²²⁶Ra, ²³²Th and ⁴⁰K activity concentrations and of the gamma-index [2] and radium-equivalent [3, 4] calculation. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K result in the order of 100, 50 and 500 Bq kg^-1, respectively. Gamma index and radium equivalent activity have been found well below the acceptable limit in most of the samples.