Cloud Chamber

Instructions

• Remove the plastic lid from the glass cloud chamber and soak the gray foam with ethanol, or highly concentrated isopropyl alcohol (93% or higher).
• Place the radioactive source (Pb-210) into the container as shown above. Replace the lid, and let the chamber sit for 10 minutes while the ethanol evaporates and fills the chamber.
• Remove the glass chamber from the base, and pour liquid nitrogen (about 2 or 3 inches deep) into the styrofoam container that rests in the bottom of the base. Or, if you have crushed dry ice, remove the styrofoam cup and place the crushed dry ice into the metal cup of the base. (note: dry ice is nice because it lasts longer, but LN2 cools the plate down much quicker.)
• Place the chamber back onto the base such that the metal rod dips into the liquid nitrogen when the chamber rests on the base. Or, if dry ice is used, insert the metal rod into the dry ice.
• After 10 or 15 minutes of cooling down, clouds of supersaturated alcohol will form in a thin layer above the black plate. Alpha particles or cosmic rays that streak through the alcohol cloud ionize the alcohol and cause it to condense along the particle's path. These tracks are visible.
• The circular light in the base, below the chamber, allows for better viewing of particle tracks. If light doesn't initially work, hold button down for several seconds.
• Getting the alcohol cloud to form is a little bit tricky. Before attempting this demo in class, try it out.

Located in L01, section C1.