1. Natural radioactivity of drinking water in Finland;Asikainen;Health Phys.,1980
2. Method for direct measurement of radium and radon in spring waters;Bizollon;Ann. Phys. Biol. Med.,1971
3. 222Rn In ground water In Nigeria;Farai;Health Phys.,1992
4. Natural radioactivity of fresh waters in Poland;Grzybowska;Pol. Arch. Hydrobiol,1983