Presence of a radioactive gas in archaeological excavations, determination and mitigation

Abstract

During recent archaeological discovery and excavation of a tunnel build approximately 2000 years ago by the Teotihuacans under the feathered serpent temple, in Mexico, abnormal radon concentrations up to 700Bqm−3 were measured at several excavation stages. The tunnel is at 15m below the earth surface with a vertical rectangular entrance of 4×4m2, a semi cylindrical shape of 3m in diameter, with a probable length of 100m.This study supports the assumption that at the opening of the tunnel radon concentration was around 5500Bqm−3; however, although natural convection in the tunnel atmosphere naturally pups radon out, it build up to a maximum concentration of 2000Bqm−3. This paper presents the identification of the radon problem in this archaeological site, dose determination, and the mitigation actions that reduced the radon concentration down to 40Bqm−3 that ensure a negligible radon risk for archaeologist.