Strontium-90
Strontium Sr-90 is a radioactive isotope of the heavy metal strontium, Strontium-90 is a by-product of uranium and plutonium fission. SR-90 is linked to bone, and other, cancers. Acting chemically in vivo like calcium, it tends to concentrate in bones and teeth. Used as a radioactive tracer in medical and agricultural studies, controlled amounts of strontium-90 have also been used as a treatment for bone cancer. (NCI04)