Sources

Websites:

http://www.iaea.org/Publications/Factsheets/English/radlife.html#risks

http://www.aboutnuclear.org/view.cgi?fC=Radiation_and_Radioactivity,Benefits_of_Radiation

http://www.sciencenetlinks.com/lessons.cfm?BenchmarkID=4&DocID=424
http://www.nirond.be/engels/6.3.3_gevaar_eng.html
http://www.darvill.clara.net/nucrad/danger.htm

http://www.phyast.pitt.edu/~blc/book/chapter5.html

http://en.wikipedia.org/wiki/Background_radiation

http://www.theodoregray.com/PeriodicTable/Posters/Poster2.2000.low.JPG

http://www.theodoregray.com/PeriodicTable/Elements/Radioactive/index.s7.p2.html

http://simple.wikipedia.org/wiki/List_of_common_elements

http://www.lbl.gov/abc/wallchart/chapters/03/4.html

http://www.mlahanas.de/Physics/Bios/images/HenriBecquerel.jpg

Paper:

Scientific American Science Desk Reference

Periodic Table