1. Ra-226 and radium-228 in Tejo river ecosystems;Carreiro,1989
2. Principles of Isotope Geology;Faure,1977
3. Measurements of radioactivity levels in soil in the Nile Delata and middle Egypt;Ibraheim;Hlth Phys,1993
4. The natural distribution of radium;Iyengar,1990
5. Tables of Isotopes;Lederer,1986