Thoron (220Rn) in the indoor environment

Many locations around the world have higher levels of natural background radiation due to elevated levels of primordial radio nuclides in the soil and their decay products, like radon (222Rn), and thoron (220Rn) in the environment. Of late, technologically enhanced naturally occurring radioactive material has also contributed to the burden of background radiation. Since the contribution from inhalation of 222Rn, 220Rn and their short lived progenies contributes more than 54% of the total background radiation dose, it was necessary to supplement the external component with inhalation component. This component is not adequately estimated for the country so far on a national level. With this in mind, a national survey has been executed by this center involving a large number of universities and other allied research institutions from different parts of the country for the estimation of inhalation component of the dose rate arises from 222Rn, 220Rn and their short-lived progenies. This survey has been carried out using a twin cup radon-thoron dosimeter with solid state nuclear track based dosimeter developed and standardized at Bhabha Atomic Research Centre, Mumbai using LR-115 Type-II, of 12μm thick cellulose nitrate film as a detector. In this paper the contribution from 220Rn and its progenies to the inhalation component is presented. Present study reveals that 220Rn and its progeny contributes nearly 20% of the total dose rate to radon, thoron and their progenies. Paper presents the method measurements and the results obtained. Data available in literature is also compared. (author)