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2. Radium-226 in environmental materials and foods;De Bortoli;Health Phys,1972
3. Evaluation of Household Budgets in 1995, Table 54: available in Main Statistical Office, Warsaw, Poland (in Polish).
4. The daily intake of 234,235,238U, 228,230,232Th and 226,228Ra by New York City residents;Fisenne;Health Phys,1987
5. Guidelines for Drinking-Water Quality, 1. 2nd Geneva: WHO, 1993.