Wilson cloud chamber, piston compression type.

Wilson cloud chamber, piston compression type. Giving a short strong pull on the handle of this Wilson expansion cloud chamber causes __ray tracks from a radium source to become briefly visible. This is a Wilson expansion cloud chamber. The top sealed glass cylinder is filled with air. There is a small radium radioactive source (5-10 mc) fitted into the bottom base plate. The source emits positive _ rays (helium nuclei), and _ rays (photons). The _ rays knock electrons off of nitrogen and oxygen in the air, leaving a trail of negative and positive ions, but the _ rays produce few ions. The _ rays leave a strong trail of ions, and the _ rays do not leave an ionized trail. In the base is a felt pad soaked with a 50% mixture of methanol and water. When the handle of the hand pump is pulled quickly and held, the air temperature is temporarily lowered and the air becomes supersaturated with methanol vapor which condenses on the positive and negative ions left by the __rays, leaving visible trails. A slide projector light source helps to illuminate the trails. A 'clearing field' potential difference of 200-500 volts is placed across the top and bottom of the cylinder to clear the air of ions so that new tracks can be seen. A TV camera can be used to display the tracks on a monitor.