Radioactive Materials

Example: \ce{^{131}_{53}I} has a half-life of 8.07 days. If you initially have 10 kg of \ce{^{131}_{53}I}, how much will you have in 3 weeks?


  • half-life = 8.07 days
  • period = 3 weeks = 21 days
  • initial amount = 10 kg


  • Remaining amount? (kg)

Remaining=original\times(\frac{1}{2})^{t}\ \rightarrow\ m_{final}=m_{initial}(\frac{1}{2})^{t}

t=\frac{period\ of\ time}{half-life}=\frac{21\ days}{8.07\ days}=2.6=t

m_{final}=10\ kg\times(\frac{1}{2})^{2.6}

m_{final}=1.649\ kg\ of\ \ce{^{131}_{53}I}


Radioactive Decay

Alpha decay: α

  • High energy proton (H^{+})
  • Can be stopped by a piece of paper

Beta decay: β

  • High  energy electron (e^{-})
  • Can be stopped by a sheet of metal

Gamma radiation: γ

  • High energy ray of light that is produced in the balancing of linear and angular momentum in nuclear reactions
  • Can be stopped by 5 inches of high density material like lead. Several feet of lead and concrete are usually used.