1) Strontium-90 (⁹0Sr) is produced by nuclear explosions and reactor accidents (Chernobyl,

Fukushima) and can replace calcium in bones, where it stays. Its radioactive decay has a

half-life of 28.1 years and causes bone cancer. If 1 ug is absorbed by a newly born baby.

how much will remain in their body after 18 years and after 70 years?