[Paul123 (OP)]

Does anyone know the activity of strontium-90? Any webs links would also be appreciated.

[another_someone]

Strontium is chemically similar to calcium (but more reactive), and so readily insinuates itself into bone.  Strontium-90 is radioactive, so once it gets into the bone, it will slowly destroy it (and the marrow).

http://www.epa.gov/radiation/radionuclides/strontium.htm
http://en.wikipedia.org/wiki/Strontium