Journal of Environmental Radioactivity 47 (2000) 291}300 Concentrations of Rn, Ra and Ra in surface sea water of the Bay of Bengal Satyajit Ghose*, M.N. Alam, M.N. Islam Radioactivity Testing and Monitoring Laboratory, Bangladesh Atomic Energy Commission, P.O.Box. No. 1352, Chittagong, Bangladesh Department of Physics, University of Chittagong, Chittagong, Bangladesh Received 17 August 1998; accepted 6 April 1999 Abstract Concentrations of Rn, Ra and Ra in surface sea water of the Karnaphuli river estuary, near-shore and o!-shore regions of the Bay of Bengal were measured using a p-type coaxial high purity Ge detector along with in situ measurement of air and water temperature, salinity, pH and tides of the water. The activities of Ra and Ra were in a range of 5.4$2.4}29.0$8.3 mBq l and 3.0$2.0}7.6$3.7 mBq l, respectively. These values are compared with concentrations reported for other countries of the world.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Radium; Radon; Sea water; Bay of Bengal 1. Introduction In marine environments, natural radionuclides mainly result from the weathering and recycling of terrestrial minerals and rocks and from primordial nucleo-synthesis. Distributions of natural radionuclides in the marine environment depend on their physical, chemical and geological properties (Broecker & Peng, 1982; Pentreath, 1984). There are two isotopes of Ra readily detectable in sea water, Ra and Ra, with half-lives of 1602 and 5.8 years, respectively. They occur in the sea water pri- marily by di!usion from sediments via the interstitial water (Broecker, Kanfonan * Corresponding author. Tel.: # 880-31-618017; fax: # 880-31-618017. E-mail address: rtl@globalctg.net (S. Ghose) 0265-931X/99/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 5 - 9 3 1 X ( 9 9 ) 0 0 0 4 6 - 6