Radiological hazard assessment at the Monte Bello Islands

Field and laboratory measurements are described and data presented which enabled dose assessments for exposure to artificial radionuclides at the Monte Bello Islands, the sites of U.K. atomic weapons tests in 1952 and 1956. The report focuses on quantifying the inhalation hazard as exposure via the ingestion and wound contamination pathways is considered inconsequential. Surface soil concentrations of radionuclides and particle size analyses are presented for various sampling sites. Analyses of the distribution with depth indicated that, in general, the activity is more or less uniformly mixed through the top 40 mm, although in a few cases the top 10 mm contains the bulk of the activity. The239Pu/241Am activity ratios were measured for selected samples. The only potential hazards to health from residual radioactive contamination on the Monte Bello Islands are due to the inhalation of actinides (specifically plutonium and americium) and from the external gamma-radiation field. Only one area, in the fallout plume of HURRICANE to the north-west of Main Beach, is a potential inhalation hazard. For an average inhalable dust loading of 0.1 mg/m3, three days occupancy of the most contaminated site will result in a committed effective dose equivalent of 1 mSv. The two ground zeros could not be considered inhalation hazards, considering the small areas concerned and the habits of visitors (full-time occupancy, over a period of one year or more, of the most contaminated sites at either of the G1 or G2 ground zeros would be required to reach 1 mSv). 25 refs., 23 tabs., 3 figs