Create a radioactive cloud in your classroom with this safe and easy student activity. Simply place the alcohol-soaked blotting paper inside the clear plastic chamber and place the chamber on dry ice. After inserting the included harmless thorium nitrate radioactive source in the side of chamber, the alpha particles emitted cause the alcohol vapor in the path of the particles to condense, forming visible vapor trails. Denatured ethyl alcohol, a 300 W light source, and dry ice, all required, are available separately. Size of chamber: 3 1/2″ dia x 1 1/2″H.