RADIOLOGICAL ASSESSMENT OF THE RIBBLE ESTUARY .2. BETA-DOSE-RATES ANDGAMMA-DOSE-RATES AND DOSES TO CRITICAL GROUPS

The mean background beta dose and gamma kerma rates measured in the Ri bble Estuary were 0.16 +/- 0.14 mu ASv h(-1) and 64 +/- 8.5 nGy h(-1), respectively. Maximum total dose rates arising from radionuclides dis charged from BNFL Sellafield and Springfields were 130 nGy h(-1) in ai r for gamma emissions at 1 m above the sediment and 19 mu Sv h(-1) to skin for beta emissions at 30 cm above the sediment. The maximum gamma air kerma rate was principally comprised (64%) of Sellafield-derived radionuclides and was located on the established salt marshes. The bet a dose is almost entirely (95%) due to Springfields' derived radionucl ides and is associated with fine-grained sediments in the upper reache s of the estuary. By means of posted questionnaires, time-lapse video photography and person-to-person questioning, the habits of the people who use the Ribble Estuary principally for recreation were assessed. The results were used to calculate the effective dose and organ doses from external irradiation and inhalation exposure to radioactivity ori ginating from both Sellafield and Springfields discharges. The maximum excess dose was 73 mu Sv year(-1) for a walker and bird-watcher with an occupancy of 2080 h annually. This is half the dose received by the critical group (house boat dwellers) identified and assessed by MAFF. All other excess doses were below this value. (C) 1997 Elsevier Scien ce Limited.