Indoor thoron and radon concentrations in Zhuhai, China

A field survey of 54 dwellings and 21 points outdoors around Zhuhai area was carried out using a newly developed integrating monitor in the spring of 2001 for a preliminary exposure assessment on Rn-222 and Rn-220 progeny, focusing especially on Rn-220 progeny levels and its contribution to the general public. The flux rates of Rn-222 and Rn-220 from ground soil and soil nuclide contents were measured Simultaneously. The average EECRn and EECTn were 52.9 +/- 39.1 Bq(.)m(-3) and 4.0 +/- 2.3 Bq(.)m(-3) for dwellings and 7.5 +/- 3.6 Bq(.)m(-3) and 0.6 +/- 0.2 Bq(.)m(-3) for outdoor air, respectively. Rather high Rn-220 flux rates from ground surface were measured, the mean value was 2,645.1 +/- 1,667.6 mBq(.)m(-2.)s(-1). The estimated radiation exposures from the exhalation of Rn-222 and Rn-220 progeny were 3.3 mSv(.)a(-1) and 1.1 mSv(.)a(-1), respectively. The exposure from Rn-220 progeny was some 1/3 that of Rn-222 progeny, and ought not to be ignored from the viewpoint of radiation protection in Zhuhai area.